Geochemical Diversity of Near-Ridge Seamounts

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Geochemical Diversity of Near-Ridge Seamounts Insights into Oceanic Magmatic Processes and Sources through Trace Element and Isotopic Chemistry
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Hann, Nichelle L
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Doctorate ( Ph.D.)
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University of Florida
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Geology, Geological Sciences
Committee Chair:
Perfit, Michael R
Committee Members:
Min, Kyoungwon Kyle
Mueller, Paul A
Foster, David A
Hobert, James P

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Subjects / Keywords:
depleted -- enriched -- lamont -- morb -- ocean -- ridge -- seamount -- vance
Geological Sciences -- Dissertations, Academic -- UF
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Geology thesis, Ph.D.
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Abstract:
Basaltic lavas from seamounts formed near mid-ocean ridge (MOR) spreading centers offer an opportunity to investigate variations in the composition of and melting in the sub-oceanic mantle as well as crusta lmagmatic processes that are masked by homogenization processes that occur beneath ridge axes. This dissertation presents new major element, trace element, and isotopic data from a suite of basalts erupted from individual, near-ridge seamounts and the Vance seamount chain along the Juan de Fuca Ridge (JdFR) and the Lamont seamount chain adjacent to the northern East Pacific Rise (EPR). Overall, lavas that comprise near-axis seamounts range to more primitive compositions (higher MgO concentrations) and have more variable trace element and isotopic signatures than associated MOR basalts. In addition, some lavas from near-axis seamounts are more incompatible element-depleted than basalts from adjacent MOR. Rogue seamount, located to the east of the Coaxial segmentof the JdFR, hosts basalts that are the most depleted of any samples thus far documented along the JdFR. Incompatible element-enriched compositions are quite rare, having only been sampled on the oldest seamount (furthest from the ridge) of the Vance seamount chain. Melting models indicate that the most depleted off-axis basalt compositions found at the Vance seamount chain, the Lamont seamount chain, and Rogue seamount cannot be produced by melting of DMM mantle Workman and Hart, 2005 under typical ridge melting conditions. This indicates that the mantle source of the depleted basalts is either more trace element-depleted than typical ridge mantle or that mantle melting temperature is higher. Considering the entire range of near-axis seamount compositions along the JdFR, the isotopic variability indicates that they formed from melting and mixing ofa two-component mantle composed of a depleted component isotopically similar to a very depleted DMM mantle end member and a more enriched component similar tothe HIMU mantle end member (both described by Zindler and Hart 1986).Compared to JdFR seamount lavas, there is less isotopic variability in Lamont seamount basalts, but these lavas exhibit the same general isotopic trends as JdFR off-axis lavas and likely formed in a similar manner. However, some Lamont samples have anomalously high Al2O3 and Sr concentrations, that is likely due to assimilation of a trace element-depleted gabbro as primitive melts traverse preexisting seamount crust.
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by Nichelle L Hann.
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Thesis (Ph.D.)--University of Florida, 2012.
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Adviser: Perfit, Michael R.
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RESTRICTED TO UF STUDENTS, STAFF, FACULTY, AND ON-CAMPUS USE UNTIL 2013-08-31

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1 GEOCHEMICAL DIVERSITY OF NEAR RIDGE SEAMOUNTS: INSIGHTS INTO OCEANIC MAGMATIC PROCESSES AND SOURCES THROUGH TRACE ELEMENT AND ISOTOPIC CHEMISTRY By NICHELLE LYNN HANN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2012

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2 2012 Nichelle Lynn Hann

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3 To my husband Jared

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4 ACKNOWLEDGMENTS This dissertation has only come to completio n because of the generous support and contributions of many people. First and foremost, I thank my husband Jared for all the support he has given me. He has been there for me at every step and his patience has been greatly appreciated. I also thank my pare nts for raising me to love nature and science. I am grateful for all the assistance and guidance my advisor Dr. Mike Perfit has given me over the last four years. He has helped me to link geochemical characteristics to a variety of geologic settings and ha s helped me to better understand the mid ocean ridge system as a whole. He has also enabled me to travel to scientific conferences where I have been able to share my research and receive feedback on my results. I would also like to recognize the support an d guidance of Dr. Rachel Walters. With her assistance, my knowledge and ability to calculate geochemical models has greatly improved. Dr. George Kamenov was also of great help in training me in lab and analysis techniques. Thank you to my committee members as well for their suggestions and feedback on my results and for challenging me to think more deeply about the implications of my research. I would also like to acknowledge the National Science Foundation for funding this project, as well as Dr. Dave Clag ue of the Monterey Bay Aquarium Research Institute for giving me the opportunity to gain valuable experience on a research cruise.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 LIST OF ABBREVIATIONS ................................ ................................ ........................... 10 ABSTRACT ................................ ................................ ................................ ................... 12 C HAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 14 2 GEOCHEMISTRY OF BASALTS ERUPTED AT THE VANCE SEAMOUNT CHAIN: INSIGHTS INTO MANTLE SOURCE AND MELTING PROCESSES ........ 16 A Review of Near Ridge Seamount Chains ................................ ............................ 16 Geologic Background ................................ ................................ ....................... 17 Regional Geology ................................ ................................ ............................. 18 Methods ................................ ................................ ................................ .................. 19 Field Methods ................................ ................................ ................................ ... 19 Geochemical Methods ................................ ................................ ...................... 20 Results ................................ ................................ ................................ .................... 22 Major Element Glass Chemistry ................................ ................................ ....... 22 Trace Element Geochemistry ................................ ................................ ........... 24 Sr Nd Pb Isotopic Geochemistry ................................ ................................ ...... 26 Discussion ................................ ................................ ................................ .............. 27 Comparison to Nearby Ridge Segments ................................ .......................... 27 Fractionation Models and Implications for the Presence of Magma Chambers Beneath the Vance Seamount Chain ................................ ........... 29 The Effect of Source Melting on Melt Composition ................................ ........... 31 Model assumptions and parameters ................................ .......................... 32 Constraints on melting depleted mantle ................................ ..................... 33 The Effect of Ridge Migration on Mantle Melting ................................ .............. 37 Summary ................................ ................................ ................................ ................ 38 3 THE GEOCHEMISTRY OF BASALTS ERUPTED OFF AXIS ALONG THE JUAN DE FUCA RIDGE: IMPLICATIONS FOR MANTLE SOURCE HETEROGENEITY AND MIXING ................................ ................................ ........... 56 Prior Research on Near Ridge Seamounts ................................ ............................. 56 Regional Geology ................................ ................................ ................................ ... 57 Methods ................................ ................................ ................................ .................. 60

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6 Results ................................ ................................ ................................ .................... 61 Major Elements ................................ ................................ ................................ 61 Trace Elements ................................ ................................ ................................ 62 Iso topic Ratios ................................ ................................ ................................ .. 63 Discussion ................................ ................................ ................................ .............. 64 Mantle Source Characteristics ................................ ................................ .......... 64 T wo component Mantle Melting and Mixing ................................ ..................... 65 Origins of JdFR Mantle Components ................................ ............................... 68 Summary ................................ ................................ ................................ ................ 71 4 THE LAMONT SEAMOUNTS REVISITED: GEOCHEMICAL SIGNATURES OF MANTLE SOURCES AND MELTING PROCESSES AND CRUSTAL ASSIMILATION PROCESSES ................................ ................................ ............... 86 A Review of the Lamont Seamount Chain ................................ .............................. 86 Background ................................ ................................ ................................ ...... 87 Prior Research ................................ ................................ ................................ 87 Methods ................................ ................................ ................................ .................. 89 Results ................................ ................................ ................................ .................... 90 Trace Elements ................................ ................................ ................................ 90 Isotopic Ratios ................................ ................................ ................................ .. 91 Discussion ................................ ................................ ................................ .............. 92 Possible Origins of High Al, High Sr Basalts ................................ .................... 92 Mantle Sources, Heterogeneity and Melting ................................ ..................... 97 Summary ................................ ................................ ................................ .............. 100 5 CONCLUSION ................................ ................................ ................................ ...... 113 A PPENDIX A REPRODUC IBILITY AND ACCURACY OF ICP MS TRACE ELEMENT ANALYSIS FOR AGV 1 AND 2392 1 ................................ ................................ ... 114 B TRACE ELEMENT AND ISOTOPIC RATIOS OF VANCE SEAMOUNT BASALTS ................................ ................................ ................................ .............. 119 C MAJOR ELEMENT, TRACE ELEMENT, AND ISOTOPIC RATIOS OF JDFR OFF AXIS BASALTS ................................ ................................ ............................ 138 D TRACE ELEMENT AND ISOTOPIC RATIOS OF LAMONT SEAMOUNT BASALTS ................................ ................................ ................................ .............. 144 LIST OF REFERENCES ................................ ................................ ............................. 151 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 161

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7 LIST OF TABLES Table page A 1 Reproducibility and accuracy for trace element data for AGV 1 ....................... 115 A 2 Reproducibility and accuracy for trace element data for 2392 .......................... 117 B 1 Major and trace element concentrations and isotopic ratios from basalts from the Vance seamount chain and the Vance ridge segment ............................... 120 C 1 Major element trace element, and isotopic analyses of seamount basalts along the southern JdFR ................................ ................................ .................. 139 C 2 Model parameters for DMM HIMU mixing models ................................ ............ 143 D 1 Trace element and isotopic ratios of basalts from the Lamont seamount chain 145

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8 LIST OF FIGURES Figure page 2 1 Location maps of the Vance seamount chain ................................ ..................... 40 2 2 Major element compositions of Vance seamount basalts ................................ ... 41 2 3 MgO concentration versus selected trace elements ................................ ........... 43 2 4 Chondrite normalized REE and mantle normalized diagrams of Vance seamount basalts and Vance segment basalts ................................ .................. 45 2 5 Trace element variations in Vance seamount basalts ................................ ........ 47 2 6 Selected Vance seamount major element and trace element compositions and isotopic ratios versus distance from the ridge. ................................ ............. 48 2 8 Selected major and trace element results for fractional crystallization models for Vance seamount samples ................................ ................................ ............. 51 2 9 Model REE inversi ons ................................ ................................ ........................ 52 2 10 Results of alphaMELTS melting models ................................ ............................. 54 2 11 Illustration of possible model to explain the variable geochemistry see n at the Vance seamount chain ................................ ................................ ....................... 55 3 1 Location map showing study areas off axis volcanism along the Juan de Fuca Ridge ................................ ................................ ................................ ......... 72 3 2 Maj or element compositional variations of individual seamount basalts ............. 73 3 3 Trace element ratio plots of off axis seamount basalts ................................ ....... 75 3 4 Chondrite normalized REE and primitive mantle normalized diagrams of individual seamount samples ................................ ................................ .............. 76 3 5 Variations in Sr, Nd, and Pb isotope compositions for individual seamounts ..... 77 3 6 Selected isotopic ratios of JdFR lavas in comparison to mantle end member compositions ................................ ................................ ................................ ....... 78 3 7 Results of isotopic mixing model ................................ 79 3 8 Isotopic and trace element mixing models ................................ .......................... 80 3 9 Selected trace element and isotopic ratios versus latitude ................................ 81

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9 3 10 Results of alphaMELTS melting model ................................ ............................... 83 3 11 Variations in 206 Pb/ 204 Pb versus several incompatible element ratios ................. 84 3 12 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb showing calculated ages for Pb Pb arrays for selected JdFR ridge segments and off axis seamounts ................................ ..... 85 4 1 Map of the Lamont seamount chain ................................ ................................ 101 4 2 Major element plots showing Lamont glasses ................................ .................. 102 4 3 Comparison of Lamont glass reanalysis for selected trace elements and isotopes ................................ ................................ ................................ ............ 103 4 4 Plots of MgO concentrations versus a set of tr ace elements ............................ 104 4 5 Plots of trace elements versus trace element ratios comparing Lamont basalts and EPR basalts ................................ ................................ .................. 106 4 6 Chondr ite normalized REE and mantle normalized diagrams of Lamont basalts in comparison to EPR N MORB ................................ ........................... 107 4 7 Plots of Sr Nd Pb isotopic ratios in comparison to EPR basalts ....................... 109 4 8 Trace element ratios versus 143 Nd/ 144 Nd ................................ .......................... 110 4 9 Major and trace element assimilation models for gabbro composition and N MORB and Lamont melts ................................ ................................ ................. 111 4 10 Trace element melting model ................................ ................................ ........... 112

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10 LIST OF ABBREVIATION S DMM Depleted MORB Mantle DDMM Depleted Depleted MORB Mantle DTop Depth to the top of the melting column E MORB Enriched mid ocean ridge basalt EPR East Pacific Rise HREE Heavy rare earth element HIMU High mantle ICP MS Inductively coupled mass spectrometer INAA Instrumental neutron activation analysis JdFR Juan de Fuca Ridge LILE Large ion lithophi le element LREE Light rare earth element Ma Million years ago MBARI Monterey Bay Aquarium Research Institute MC ICP MS Multi collector inductively coupled mass spectrometer MOR Mid ocean ridge MORB Mid ocean ridge basalt MREE Middle rare earth element N MO RB Normal mid ocean ridge basalt OA Off axis REE Rare earth element ROV Remotely operated vehicle TIMS Thermal ionization mass spectrometry USGS United States Geological Survey

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11 V Volt XRF X ray fluorescence

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12 Abstract of Dissertation Presented to the Gr aduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy GEOCHEMICAL DIVERSITY OF NEAR RIDGE SEAMOUNTS: INSIGHTS INTO OCEANIC MAGMATIC PROCESSES AND SOURCES THROUGH TRACE ELEMENT AND ISOTOPIC CHEMISTRY By Nichelle Lynn Hann August 2012 Chair: Michael R. Perfit Major: Geology Basaltic lavas from seamounts formed near mid ocean ridge (MOR) spreading centers offer an opportunity to investigate variations in the composition of and melting in the sub oceanic mantle as well as crustal magmatic processes that are masked by homogenization processes that occur beneath ridge axes. This dissertation presents new major element, trace element, and isotopic data from a suite of basalts erupted from individual, near ridge seamounts and the Vance seamount chain along the Juan de Fuca Ridge (JdFR) and the Lamont seamount chain adjacent to the northern East Pacific Rise (EPR). Overall, lavas that comprise near axis seamounts range to more p rimitive compositions (higher MgO concentrations) and have more variable trace element and isotopic signatures than associated MOR basalts. In addition, some lavas from near axis seamounts are more incompatible element depleted than basalts from adjacent M OR. Rogue seamount, located to the east of the Coaxial segment of the JdFR, hosts basalts that are the most depleted of any samples thus far documented along the JdFR. Incompatible element enriched compositions are quite rare, having only

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13 been sampled on t he oldest seamount (furthest from the ridge) of the Vance seamount chain. Melting models indicate that the most depleted off axis basalt compositions found at the Vance seamount chain, the Lamont seamount chain, and Rogue seamount cannot be produced by me lting of DMM mantle [Workman and Hart, 2005] under typical ridge melting conditions. This indicates that the mantle source of the depleted basalts is either more trace element depleted than typical ridge mantle or that mantle melting temperature is higher. Considering the entire range of near axis seamount compositions along the JdFR, the i sotopic variability indicates that they formed from melting and mixing of a two component mantle composed of a depleted component isotopically similar to a very depleted DMM mantle end member and a more enriched component similar to the HIMU mantle end member (both described by Zindler and Hart [1986]). Compared to JdFR seamount lavas, there is less isotopic variability in Lamont seamount basalts, but these lavas exhibit t he same general isotopic trends as JdFR off axis lavas and likely formed in a similar manner. However, some Lamont samples have anomalously high Al 2 O 3 and Sr concentrations, that is likely due to assimilation of a trace element depleted gabbro as primitive melts traverse preexisting seamount crust.

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14 CHAPTER 1 INTRODUCTION With more detailed bathymetric mapping and sampling and the advent of new more precise technologies, researchers have realized that eruptions away from the axis of mid ocean ridges (MOR) are more common than originally thought (e.g. Shen et al. 1993; Goldstein et al. 1994, Perfit et al. 1994, Perfit and Chadwick, 1998). Young off axis eruptions have been documented up to ~80 km away from the ridge [Shen et al., 1993], although most are fo und between 5 and 15 km [Alexander and Macdonald, 1996; Scheirer and Macdonald, 1995]. Reynolds and Langmuir [2000] suggested that off axis eruptions could account for ~20% of the seafloor around the northern East Pacific Rise and Shen et al. [1993] found that the off axis eruptive products represent between 1.5 to 2% of the total volume of the oceanic crust. Off axis eruptive products are commonly found as individual cones, seamounts, seamount chains, or lava flow fields located away from the main ridge ax is. The bathymetric expression and chemistry of these submarine volcanic constructs are unlike those from major hotspot volcanoes. This dissertation will focus on volumetrically important individual seamounts and seamount chains near the ridge axis along t he southern Juan de Fuca Ridge (JdFR) and the East Pacific Rise (EPR). Near axis seamounts are commonly more chemically and isotopically heterogeneous than ridge basalt s [Fornari et al., 1988a; Graham et al., 1988; Niu and Batiza, 1997; Niu et al., 2002]. For example, Graham et al. [1998] found that the isotopic variability of seamounts off the EPR represented ~80% of the full variability of Pacific MORB Individual seamounts can also host a large degree of variability. Brandl et al.

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15 [2012] found that a si ngle seamount adjacent to the northern EPR hosts basalts with the same degree of geochemical variability as all documented near axis seamounts. Researchers have hypothesized that off axis lavas are chemically heterogeneous because they do not go through t he mixing and homogenizing processes believed to occur at ridge axes [Fornari et al. 1988a; Leybourne and Van Wagoner, 1991] Consequently, because off axis lavas are less likely to have been significantly modified, they are more likely to reveal the prima ry characteristics of heterogeneous mantle components and melts, allowing us to investigate mantle melting and source variations in the near ridge environment that are masked by mixing and fractionation at the ridge axis. The following chapters will presen t major element, trace element, and isotopic results for a suite of basalts collected from individual seamounts and the Vance seamount chain located near the JdFR and from the Lamont seamount chain near the EPR. Geochemical modeling will also be presented and theories will be explored on why and how off axis volcanism occurs.

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16 CHAPTER 2 GEOCHEMISTRY OF BASA LTS ERUPTED AT THE V ANCE SEAMOUNT CHAIN: INSIGHTS INTO MANTLE SOURCE AND MELTING P ROCESSES A Review of Near Ridge Seamount Chains The majority of mid o cean ridge petrologic studies have focused on samples erupted at the ridge axis. However, as our knowledge of this setting has increased, researchers have come to realize that ridge lavas only represent mean isotopic and geochemical compositions because of their homogenization in large axial magma chambers (e.g. Rubin and Sinton [2007]). Geochemical studies of basalt s erupted at seamounts that form in close proximity to active mid ocean ridges (MOR) provide an opportunity to better understand the compositio n of shallow mantle underneath spreading ridges and how it melts in order to f orm new oceanic crust. Because near ridge seamounts are comprised of basalt s that extend to more primitive compositions and are more variable in trace element and isotopic compos ition compared to mid ocean ridge basalts (MORB) [Fornari et al., 1988a, b; Batiza et al., 1990; Davis and Clague, 2000; Niu et al., 2002] they can provide a unique view of source variations and melting processes in the shallow oceanic mantle. Near ridge seamounts commonly occur in chains but can also exist individually and have been found adjacent to slow, intermediate, and fast spreading ridges [ Fornari et al., 198 8a,b ; Batiza et al., 1989 a,b]. Near ridge seamounts and other off axis eruptions commonly h av e unique chemical compositions [Reynolds and Langmuir, 2000] and exhibit more variability than the lavas erupted at the ridge axis. Seamount compositions can range from extremely depleted tholeiites to extremely enriched alkali basalts [Batiza et al., 19 90; Niu et al., 2002]. In fact, Zindler et al. [1984] found that one seamount could have the same degree of variation as seen along several hundred

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17 kilom eters of a ridge. Because of the primitive compositions of some sample s from these seamounts, near axis seamount studies can potentially lead to a better understanding of the mantle underneath spreading ridges and can offer better insights into how melting occurs in the shallow mantle both on and off axis. Prior studies of off axis volcanism have led to n ew theories about the nature of the mantle underneath spreading ridges. A detailed study of the Lamont seamounts [Fornari et al., 1988a,b] as well as individual seamounts near the EPR [Niu and Batiza, 1997; Niu et al., 2002] indicated that these seamounts formed from a heterogeneous mantle source that was variably depleted in incompatible elements. Geshi et al. [2007] also studied off axis basalts near the EPR and suggested that the extremely depleted compositions they found in their study could be explaine d by remelting of residual, refractory mantle that had already been partially melted beneath the ridge axis. Off axis volcanism along the JdFR has not been as extensively studied as off axis seamounts along the EPR. Previously only a limited number of sa mples had been recovered from the Vance Seamounts as well as several other off axis sites along the JdFR all of which were widely spaced and imprecisely located dredge samples. Only a small subset of these samples has been geochemic ally or petrographicall y analyzed [ Finney, 1989; Smith et al., 1994 ; Wendt, 2008; Cornejo, 2008 ]. This study will report new detailed laboratory investigations of sample s from six of the seamounts in the Vance seamount chain (Fig. 2 1) and thus dramatically increases both the number of off axis samples and our understanding of off axis magmatism along the JdFR. Geologic Background The Vance seamount chain sits on the Pacific plate, intersecting the Juan de Fuca R 2 1 ) and is ju st south of

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18 Axial seamount, the current surface m anifestation of the Cobb hotspot. It is located adjacent to the Vance segment of the southern JdFR, which hosts an axial volcanic ridg e in a broad, 8 km wide valley [Carbotte et al., 2006] The chain consist s of five circular seamounts (seamounts A, C, E/D, an d F) with flat summit plateaus and breach ed calderas (some are nested) oriented towards the ridge and two less structured areas consisting of pillow ridges and cones (seamounts B and G) [Hammond, 1997] The seamounts are located on crust 0.78 t o 2.55 Ma old [Clague et al., 2000], and the presence of ridge parallel faults indicates that the cones were formed in the near ridge environment [Hammond et al., 1997] Hammond et al. (1997) studied the morphology of this chain and theorized that, as spreading caused each volcano to move leading to the formation of calderas 1 4 km across and up to 400 m deep [Clague et al ., 2000] oriented sou theastward towards the ridge Seamount heigh t ranges from 440 m to 1140 m above the surrounding seafloor [Clague et al., 2000 ] in comparison to the adjacent ridge height of ~400 m [Carbotte et al., 2006] and the seamount volumes range from 15 67 km 3 Regi onal Geology The Vance segment of the southern JdFR is bounded on the north by the Axial segment and on the south by the Cleft segment, and each of these ridge segments have unique chemical signatures. The Cleft segment is the least complex of the JdFR seg ments and appears to be the only segment that is not affected by thermal and/or chemical anomalies or enriched mantle sources. This segment produces lavas that are typical incompatible element depleted N MORB with a modest compositional range [Smith et al. 1994; Stakes et al., 2006]. The Vance segment is not as well sampled as

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19 the other segments, but limited dredge sampling indicates that the Vance segment hosts MORB that are more primitive than basalts erupted at the Cleft segment [Smith et al., 1994]. No rth of the Vance segment is the Axial segment, which is noticeably influenced by the Cobb hotspot [Chadwick et al., 2005]. This segment is composed of a large central volcano called Axial volcano with prominent rift zones running to the north and south. La vas from Axial seamount, where melt production is higher, are generally more primitive than lavas erupted along the Axial segment rift zones (although some primitive cones have been documented along the rift zones). Axial segment basalts are slightly more enriched in alkalis and highly incompatible elements in comparison to N MORB erupted at the other segments [Chadwick et al., 2005], although it is important to note that no E MORB have been documented on axis along the entire southern JdFR. Other off axis volcanic sites that are near the Vance seamount chain include the Cobb Eickelberg hotspot chain and Rogue seamount. The Cobb Eickelberg seamount chain extends ~550 km to the northwest from Axial seamount. Lavas from this chain are slightly enriched in inc ompatible elements compared to ridge lavas, but their isotopic signatures are similar to ridge basalts, suggesting to Desonie and Duncan [1990] that the Cobb hotspot is not a deep seated mantle plume but is a stationary melting anomaly in the upper mantle. Rogue seamount is an individual seamount located 16 km to the east of Coaxial segment. Samples from this seamount are the most depleted in incompatible elements of any basalts thus far analyzed along the JdFR (see Chapter 3). Methods Field Methods This s tudy uses samples collected from several research cruises Dredge samples from Seamounts F and E were collected by dredge in 1988 and were detailed in Smith

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20 et al. [1994] Individually located g rab samples from the Vance s eamounts A, B, C, E, F, and G were collected in 2006 aboard the R/V Western Flyer equipped with the ROV Tiburon both of the Monterey Bay Aquarium Research Institute (MBARI). Geochemical M ethods Initial sample preparation was conducted on ship where samples were described and catalogued an d quenched lava rinds were separated for subsequent preparation and analysis. Glass fragments from quenched lava rinds were selected for major element, trace element, and isotopic analysis. Glass chips were cleaned in a n H 2 O HCl H 2 O 2 acid mix ture in a soni cator, and the cleanest glass chips (free of phenocrysts, alteration, or Mn oxide crust) were hand picked for analysis using a binocular microscope. For trace element and isotopic analysis, ~50 mg of hand picked glass chips were added to 7 mL Teflon Savil lex hexavials (trace elements) or small round vials ( isotopes ) that had been pre cleaned in 14 N HNO 3 for 24 hours and then in 14 N HCl for 24 hours, followed by 24 hour hotplate reflux in 6 N HCl. The glass chips were leached one more time (to remove any ha ndling contamination and residual alteration ) in 1 mL 2N optima grade HCl + 2 mL 4X H 2 was then removed, 2 mL of 4X H 2 O was added and the vials were put on the hot plate for another ten minutes. The liq uid was removed and the leached glass chips were then brought to dryness. The glass chips then were dissolved in 1 mL of optima grade HF + 2 mL of optima grade HNO 3 samples were evaporated to dryness. For trace element analysis ~4.5 mL of 5% HNO 3 + 100 ppm HF spiked with 8 ppb of Re and Rh were added to the evaporated residue of each sample and each sample

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21 was capped and dissolved overnight. A procedural blank was included in each run of samples to ch eck for contamination and purity of the acids used. Each unknown was diluted 2000x and was analyzed using a multi resolution magnetic sector Element2 Inductively Coupled Plasma Mass Spectrometer (ICP MS) at the University of Florida, Department of Geologic al Sciences after Goss et al. [2010]. Analyses were externally calibrated using both USGS standards (AGV 1, BIR 1, BHVO 1, and BCR 1) and an internal standard (Endeavor Ridge MORB standard). To assess data accuracy and reproducibility as well as instrument al drift, two standards 2392 1 and AGV 1 were analyzed multiple times (n=9 and n=8 respectively; see Appendix A). For AGV 1, long term reproducibility is better than 3% for most trace elements. Long term reproducibility for 2392 1 is slightly higher becaus e this basalt is more depleted in the most incompatible elements. Most elements are better than 5 %, but trace elements with extremely low concentrations have long term reproducibility that is less precise (Rb: 11%; Zr, Th: 9%; Ba, U: 10%; Pb: 21%). An i nitial set of 24 samples were prepared and analyzed for their Sr, Nd, and Pb isotopic ratios at Carlton University and lab procedures are detailed in Cornejo [2008]. Subsequent isotopic analysis of additional samples from the Vance seamounts and the adjace nt Vance ridge segment was performed at the University of Florida. After glass dissolution, e vaporated residues were run through chromatographic elemental separation to collect Pb, Sr, and Nd. Pb was separated using anion exchange techniques in HBr e ffl uen t using 100 L Teflon columns packed with Dowex AG1X 8 anion exchange resin (100 200 mesh). Sr and Nd were then separated from the Pb column effluent using standard chromatographic methods. Sr was collected using

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22 Biorad AG50W resin columns. Subsequent p urification of the Sr fraction was achieved using 100 L Teflon columns packed with Eichrom Sr Spec resin. Separation of Nd from the REE fraction was achieved using 100 mL columns of HDEHP coated resin [ Pin and Zalduegui, 1997] The Nu Plasma multi c ollector (MC) ICP MS at the University of Florida was used to analyze samples for Sr, Nd, and Pb isotopic ratios. Analyte fractions were diluted in 2 % HNO 3 and were aspirated to produce between ~2 and 8 V of total ion current. The Tl mass bias normalizati on technique of Kamenov et al. [2004] was used to measure Pb isotopic ratios. Standards NBS 981 (Pb isotopic ratios), JNdi 1 (Nd isotopic ratios), and NBS 987 (Sr isotopic ratios) were used to assess data accuracy and long term reproducibility. Long term v alues and reproducibility (2 ) for NBS 981 are 206 Pb/ 204 Pb: 16.937 0.004, 207 Pb/ 204 Pb: 15.489 0.004, and 208 Pb/ 204 Pb: 36.689 0.008. Long term values and reproducibility (2 ) for JNdi 1 and NBS 987 are 143 Nd/ 144 Nd: 0.51209 0.000007 and 87 Sr/ 86 Sr: 0. 71246 0.00003 [Goss et al., 2010]. Detailed discussions on lab techniques for both trace element and isotopic analysis can be found in Goss et al. [2010] Results Major Element Glass Chemistry Major element glass compositions from the Vance seamount ch ain are detailed in the theses of Wendt [2008] and Cornejo [2008]. Major element analyses from samples dredged from the Vance segment as well as some dredged samples from Seamount E and F are from Smith et al. [1994]. The abundances and covariations of maj or elements indicate that Vance seamount lavas are typical tholeiitic MORB with some noticeable

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23 differences compared to basalts erupted at the ridge (Fig. 2 2 ). Many basalt s from these seamounts are relatively primitive, with MgO concentrations greater tha n 9 wt. % compared to Vance segment basalts that have a maximum concentration of ~8.4 wt. % This difference in chemistry is seen in the rest of the major element concentrations, with Vance basalt s consistently being more heterogeneous than the Vance and Cleft ridge segments General trends within the seamount chain include increasing TiO 2 FeO T Na 2 O, and K 2 O with decreasing MgO and decreasing Al 2 O 3 and CaO with decreasing MgO. These trends are, in general, consistent with those expected from the fraction al crystallization of plagioclase, olivine, and perhaps minor clinopyroxene in more evolved basalt s. Some important distinctions in elemental abundances and variations can be drawn between the individual seamounts in the chain. Seamount C and F have the m ost primitive sample s with maximum MgO concentrations of 9.45 wt. % and 9.33 wt. % respectively. Seamount C also has the largest range in MgO concentrations with values as low as 7.34 wt. %. Most of the lavas in the chain are olivine hypersthene normative but some basalt s from Seamount A and B are slightly nepheline normative. Seamount A also hosts some lavas that have high Na8 and Ti8 (concentrations corrected for fractional crystallization to MgO: 8 wt. %, after Klein and Langmuir [1987]), as well as th e highest K 2 O concentrations ( up to 0.31 wt %) in the chain. With K/Ti values ranging from 0.1 to 0.27, Seamount A basalts represent some of the most enriched and thus some of the rarest samples recovered from the JdFR region Vance seamount B and some la vas from Seamount F are also anomalous in comparison to the othe r seamounts with higher concentrations of Al 2 O 3 (14.55 to 17.86 wt. %), Na 2 O (2.45 to

PAGE 24

24 2.97 wt. %), and TiO 2 (1.07 to 1.37 wt. %) at a given MgO concentration and lower concentrations of SiO 2 (47.78 to 50.63 wt. %). Trace Element Geochemistry Wendt [2008] analyzed ~40 lava samples from the Vance seamount chain for trace element concentrations. This study has added 27 more trace element compositions for Vance seamount lavas and five analyses f rom the Vance segment (trace element analyses from this study can be found in Appendix B). The following results will discuss the combined dataset of Wendt [2008] and this study as a whole. R epresentative plots of incompatible and compatible trace element concentrations versus MgO concentrations confirm that the seamounts have diverse trace element compositions (Fig 2 3 ). The majority of samples are normal MORB (N MORB) that are variably depleted in large ion lithophile elements (LILE) and light rare earth elements (LREE) relative to the heavy rare earth elements (HREE) as shown on REE and primitive mantle normalized variation diagrams (Fig. 2 4) In general, as sample s from the Vance seamount chain become more evolved (MgO concentration decreases), incomp atible elements (e.g. LILE, REEs, Y, Zr, Nb, Sr, Rb) increase and compatible trace elements (e.g. Cr and Ni) decrease (Fig. 2 3) Although t hese trends are likely a result of small amounts of fractional crystallization, other processes such as variation s i n source composition and/or source melting and mixing of melts with different compositions likely also play a role REE patterns as well as elemental abundances and trace element ratios (La/Sm) N (Ce/Yb) N and Zr/Y indicate that these basalt s are extremely depleted to slightly enriched in moderately to highly incompatible elements. For example, seamount samples have (La/Sm) N ratios that vary from 0.31 to 1.07 Zr/Y that ranges from 1.69 to

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25 3.86, Sr that ranges from 64 to 202 ppm, and (Ce/Yb) N that ranges f rom 0.49 to 1.59 (Fig. 2 5) The se large variation s relative to Vance segment MORB are obvious in REE and mantle normalized diagrams (Fig. 2 4) Figure 2 4 also reveal s that s amples from different seamounts have crossing REE patterns, suggesting that diffe rent degrees of partial melting of a single mantle source or several different mantle sources were involved in the formation of these lavas Of all the seamount basalts, Seamount A sample s have the highest concentrations of incompatible elements and they plot as a distinct group in many of the trace element variation plots. Their enriched trace element signatures are consistent with their high concentrations of K 2 O, both of which are typical of E MORB [ Sun et al., 1979]. In contrast, trace element concent rations reveal that Seamount C basalts are the most depleted. These lavas have some of the lowest concentrations and ratios of incompatible elements (La : 1.20 1.43 ppm; (La/Sm) N : 0.36 0.62, Zr/Y: 1.69 2.47). Seamount F is the only other seamount that hosts samples with similar trace element concentrations ((La/Sm) N : 0.31 0.66). The other seamounts have lavas with trace element concentrations that range in between the values of Seamount A and C. There is a correlation between age/distance from the ridge and enrichment and variability among the first three seamounts (Fig. 2 6; it is important to note that these correlations are based on a small sample set and the identified trends could change with the addition of more samples ). Seamount A the oldest seamount is comprised of basalts with the greatest overall chemical variability, including basalts that are the most enriched in incompatible elements Basalt compositions get progressively more depleted and less chemically heterogeneous from Seamount B to Seamou nt C.

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26 However, there is a slight enrichment trend starting with samples from Seamount E that continues to Seamount F to G. The youngest basalt s from Seamount G are relatively homogeneous and have very similar trace element concentrations to ridge axis basa lt s from the Vance ridge segment Sr Nd Pb Isotopic Geochemistry This study has added twelve new Sr Nd Pb isotopic analyses (full dataset can be found in Appendix B) to the twenty four Vance seamount samples analyzed by Cornejo [2008], as well as five n ew Sr Nd Pb analyses for the Vance segment. The results discussed below are based on the combined dataset of Cornejo [2008] and this study. Vance seamount basalts have fairly heterogeneous isotopic ratios in comparison to associated ridge basalts (Fig. 2 7 ). 87 Sr/ 86 Sr ranges from 0.70238 to 0.70279 whereas Vance segment ridge samples range from 0.70247 to 0.70253. 143 Nd/ 144 Nd ranges from 0.51305 to 0.51320 for seamount basalts compared to ridge basalts that range from 0.51314 to 0.51317. Similarly, Pb isoto pic ratios (Fig. 2 7) of the seamount lavas have a greater range than the lavas from the adjacent ridge (e.g. 206 Pb/ 204 Pb 18.12 18.81 and 207 Pb/ 204 Pb 15.44 15.54 compared to ridge lavas that have 18.43 18.47 and 15.46 15.47 respectively), although this could be due to sampling bias. Pb isotopic plots show that Vance seamount basalts lie along a linear trend with samples from Seamount F having the most unradiogenic values (minimum 206 Pb/ 204 Pb: 18.12 ) and samples from Seamount B having the most radiogenic values (maximum 206 Pb/ 204 Pb: 18.81). On a 87 Sr/ 86 Sr versus 143 Nd/ 144 Nd diagram, the Vance basalts lie on linear trends. The samples with the least radiogenic 143 Nd/ 144 Nd and 87 Sr/ 86 Sr are from Seamount F ( 87 Sr/ 86 Sr: 0.70238; 143 Nd/ 144 Nd: 0.51320), and the most radiogenic values are from seamounts A and B. Compared to the majority of samples, the more

PAGE 27

27 radiogenic basalts have either relatively high 87 Sr/ 86 Sr (Seamounts A, C, E, and G) or low 143 Nd/ 144 Nd (Seamount B) (Fig. 2 7). The greater variability in 87 Sr/ 86 Sr at relatively constant 143 Nd/ 144 Nd in the samples with the highest 87 Sr/ 86 Sr suggests that a seawater contaminated component could have been involved in the petrogenesis of some of the Vance seamount basalts. In general, the isotopic ratios of Van ce seamount samples exhibit some systematic variation with distance from the ridge axis (Fig. 2 6). Nd isotopic ratios progressively increase from S ea m oun t A to S eamoun t G, while 206 Pb/ 204 Pb and 87 Sr/ 86 Sr progressively decrease towards isotopic compositio ns observed in basalts from the ridge In detail, however, some Seamount B and F samples do not conform to this trend because of anonymously low Sr isotopic ratios. Discussion Comparison to Nearby Ridge Segments In general, Vance seamount lavas are more he terogeneous in major elements, trace elements, and isotopic ratios than JdFR ridge basalts. Seamount compositions extend to lower SiO 2 concentrations and higher MgO, Al 2 O 3 Na 2 O, and K 2 O concentrations than basalts from the Vance ridge segment as well as C left [Smith et al., 1994; Stakes et al., 2006] and Axial segments [Chadwick et al., 2005] (Fig. 2 2). In fact, the nearest lavas with similar K 2 O values to Seamount A are from the Cobb Eickelberg chain [Desonie and Duncan, 1990 ]. Vance seamount lavas are a lso distinct in that their FeO T concentrations are more variable than those documented in nearby MORB erupted at the ridge. Similarly, greater variations in trace element abundances and incompatible element ratios reflect their more heterogeneous nature. T he Vance seamounts host some of the most depleted as well as some of the most enriched

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28 samples found along the southern JdFR (Fig. 2 5). Samples from the Vance seamounts have the lowest (La/Sm) N values in comparison to nearby ridge segments. Only lavas fro m Rogue seamount, east of the Coaxial segment have lower Zr/Y, Sr, and (Sm/Yb) N values in comparison to the Vance seamounts, indicating that extremely depleted lavas exist in more than one locality along the JdFR (see Chapter 3). Isotopic data suggest tha t some Vance seamount basalts (Seamount C and F) have a source similar to Rogue seamount while others (Seamount A and B) are more radiogenic and similar to Axial and Cobb Eickelberg seamount sources (Fig. 2 7). Many Vance seamount samples (Seamount C, E, F and G) have less radiogenic Pb than Cleft and Vance ridge segment MORB, while others have more radiogenic Pb, In terms of Sr and Nd isotopic ratios, basalts from the Vance and Cleft segme nts as well as some Axial volcano, Cobb Eickelberg chain, and Vance chain samples plot within a small field on Sr Nd diagrams (Fig. 2 7). However, the anomalous Seamount B basalts with relatively high 87 Sr/ 86 Sr values and low 143 Nd/ 144 Nd are similar to mor e radiogenic lavas from Axial seamount and the Cobb Eickelberg seamount chain [Chadwick et al., 2005] Overall, Vance samples consistently plot between Rogue seamount and Axial/Cobb Eickelberg seamount chain in both trace element and isotopic ratio plots, suggesting two component mixing between a very incompatible element depleted source similar to that which produced Rogue seamount and a more enriched source similar to that expressed in Axial/Cobb Eickelberg hotspot chain lavas.

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29 Fractionation Models and Implications for the Presence of Magma Chambers Beneath the Vance Seamount Chain It is generally accepted that magmas beneath spreading ridges reside in a small lens of melt above a larger zone of crystal mush (a composite magma chamber) [Sinton and Detric k, 1992; Canales et al., 2006] These lenses are periodically recharged with more mafic magma and efficient mixing occurs in these magma chambers, causing complex mineral zoning and a fairly uni form/small compositional range [ Sinton and De trick, 1992] larg ely controlled by fractional crystallization [Perfit and Chadwick, 1998; Rubin and Sinton, 2007] However, there is considerable debate about the presence of magma chambers underneath near ridge seamou nts. Leybourne and Van Wagoner [1991] used mineralogica l information (phenocrysts lack zoning, have equilibrium compositions, and crystallized at high temperatures) as well as the primitive nature of the Heck and Heckle seamount basalts next to the northern JdFR to suggest that magma chambers are not important in the formation of these lavas. In contrast, Clague et al. [2000] suggested that near ridge seamount magma chambers could exist, but that magmas likely passed through the chambers quickly thus still produc ing hot, primitive lavas without significant min eral zoning. Fornari et al. [1988a] hypothesized that, as time progressed the magma conduits that feed seamount magma chambers would migrate as spreading at the axis proceed ed thus explaining the multiple nested calderas commonly found in near ridge seam ounts The primitive compositions of many of the Vance seamount basalts plus the fact that the lavas only contain ~1% phenocrysts of olivine and plagioclase [Cornejo, 2008] is consistent with magmas having short residence times. However, some of the observ ed major and trace element trends and

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30 the presence of moderately evolved basalts within the Vance chain suggests that at least some amount of fractional crystallization has occurred The extents of fractional crystallization were evaluated using the geoch emical modeling program Petrolog [Danyushevsky and Plechov, 2011] assuming the most MgO rich lavas were parental. C rystallization was assumed to be under anhydrous conditions and at upper to lower crustal depths (1and 3 k bars). I n general, a maximum of ~ 50% fractional crystallization of olivine, plagioclase, and clinopyroxene is needed to produce the most evolved compositions found in the Vance seamount chain. This suggests that magmas would need to reside for at least a small amount of time in a subsurfa ce magma chamber before being erupted at the surface However, as expected from the variable trace element and isotopic ratios, a single parent or liquid line of descent cannot explain the full chemical variation in all seamount lava compositions or even the variation s in individual seamount compositions (Fig. 2 8 ). The inability of crystal fractionation to generate the high Al 2 O 3 concentrations found in Seamount B and some Seamount F samples is important to note. High Al basalts have been found at many r idges, and they are usually located at slow spreading centers or close to ridge terminations or fracture zones [Eason and Sinton, 2006]. Researchers have formed several hypotheses for their formation. Eason and Sinton [2006] suggested that high pressure cr ystallization of olivine and clinopyroxene could explain the high Al, low SiO 2 lavas from the Galapagos Spreading Center. However, Laubier et al. [2012] argued that high Al melt inclusions from the FAMOUS segment of the Mid Atlantic Ridge were best explain ed by assimilation of a plagioclase bearing cumulate. This second hypothesis is consistent with the slight positive Sr and Eu

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31 anomalies found in Seamount B samples (Fig. 2 4), making gabbro assimilation a likely explanation for the high Al basalts found in the Vance seamount chain (see Chapter 4). However, more detailed investigation of these lavas is needed to fully understand their petrogenesis. The Effect of Source Melting on Melt Composition Although fractional crystallization can explain some of the ge ochemical variability in the Vance seamount chain, it clearly cannot explain the full range of trace element variation. Consequently, the effects of variable extents of mantle melting was tested utilizing the alphaMELTS modeling program [ Ghiorso et al., 20 0 2 ; Asimow et al., 200 4; Smith and Asimow, 2005; Antosheckina et al., 2010]. This program, based on thermodynamic melting laws, is not without limitations. For example, in order to match laboratory experimental melt compositions, alphaMELTS melting models have to be run at significantly higher temperatures (~60C) than what are believed to be realistic temperatures for melting the sub ridge mantle, and the program also calculates melt MgO concentrations that are 1 4 % high. These inconsistencies are believe d to be caused by overestimation of the stability of clinopyroxene during melting [Ghiorso et al., 2002]. Because of the limitations of the alphaMELTS program, REE inversion 199 1 ; Walters, 2012, personal comm. ] were used to help constrain the physical aspects of mantle melting beneath the Vance seamounts. REE inversions are kinematically based parameterizations of melting experiments and they calculate a melt fraction depth profi le that best produces the observed lava trace element composition. By using the programs INVERMEL and alphaMELTS in concert, these programs have the

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32 potential to provide a greater degree of confidence in determining the compositional and physical attribute s of mantle melting in this region. Model assumptions and p arameters For the REE inversion models, the DMM mantle composition of Workman and Hart [2005] was used as the source composition and mantle potential temperature was assumed to be 1300 C based on V ance segment crustal thickness of 6.7 7 km [Carbotte et al., 2008]. The partition coefficients of Walters et al. [in prep.] were used, and average trace element compositions of each seamount were used in the REE inversion model to produce melt depth profil es for each seamount (see Mckenzie and 1991 ] ). Calculations using alphaMELTS were made under the pMELTS setting and m antle sources were melted under continuous melting conditions with a minimum fraction of melt retained in the source ( F ) of 0.005 Each melting model began at subsolidus temperatures, assuming a mantle source mineralogy of olivine + clinopyroxene + orthopyroxene + garnet + spinel The same partition coefficients were used as those in the REE inversion models [Walters et al., in prep. ] Both Salters and Stracke [2004] and Workman and Hart [2005] calculated major and trace element compositions for the depleted MORB mantle. The composition of Workman and Hart is slightly more LREE depleted, so this composition was used to represent the source of the MORB mantle (because the seamount samples range to very LREE depleted values). Workman and Hart [2005] defined several compositions for the depleted MORB mantle including DMM and DDMM, and both of these compositions were used in the models. D MM is the average depleted mantle

PAGE 33

33 composition, while DDMM is a slightly more depleted version of DMM. The mantle was assumed to be nominally hydrous with a background concentration of 128 ppm H 2 O for DMM [ Saal et al ., 2002] and 100 ppm H 2 O for DDMM. Melt c ompositions were integrated using the simple rectangle rule, and the aggregated melt fraction was used to calculate a resulting crustal thickness after Asimow et al. [ 2001]. Constraints on melting depleted mantle REE inversion calculations produce depth p rofiles of accumulated melts that best reproduce the trace element chemistry of the basalts being studied. The modeled depth of melt initiation, the depth to the top of the melting column (DTop), and the calculated melt fractions can all be used to better understand mantle melting processes. For example, DTop values essentially are controlled by the total amount of melting that must occur to generate the observed REE abundances. For basalts from the Vance seamount chain, melt depth profiles var y from seamou nt to seamount (Fig 2 9). DTop values for seamounts A, E, F, and G are 3 0 km, 1 6 km, 16 km, and 22 km respectively indicative of significant differences in the amounts of melting that occurred beneath each of these seamounts It follows that the lowest e xtents of melting (deepest DTop) would be determined for the enriched basalts recovered from Seamount A. Calculated results for s eamount s B (Dtop: 5 km) and C (Dtop: 1 km) however, are unrealistic in that they suggest melting would have to be great enough to continue into the crust to produce the very LREE depleted basalt s observed at these seamounts. These results suggest that one or more of the assumed model input parameters are incorrect. One possible solution is that in order to produce the most deplet ed lavas in the Vance chain under normal mantle potential temperatures the source needs to be more depleted

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34 than that proposed for the DMM composition of Workman and Hart [2005] or that the melting temperature needs to be increased To test the results of the INVERMEL models, alphaMELTS was used to model melting of depleted mantle under normal mid ocean ridge conditions. A starting temperature and pressure of ~1450 C and 32 Kbars (~105 km) was chosen because these conditions produced a total model crust al thickness of 6.9 km, which is comparable to the crustal thickness of the Vance segment predicted by Carbotte et al. [2008] (6.7 7 km). Results from these models indicate that intermediate to more enriched seamount compositions are consistent with meltin g a DMM source ~5% to ~15%. The most enriched basalts from Seamount A can be formed from the smallest degree melts (~5%) and the extent of melting must progressively increase, in order to produce the more depleted melts that characterize the younger seamou nts (Fig. 2 10). However, similar to the results obtained from the REE inversion models, alphaMELTS indicates melting would need to proceed practically to the base of the crust to produce the most depleted basalt compositions at Seamount C and F. For exam ple, reasonable ridge melting scenarios are unable to reproduce the most depleted (lowest (La/Sm) N ) values found at these seamounts (Fig. 2 10). Calculated melt compositions represented on mantle normalized and REE diagrams also show the most incompatible elements and LREEs are not depleted enough in comparison to the middle REE to match the observed patterns (Fig. 2 [2005] more depleted mantle composition (DDMM) as the source composition under the same melting conditions did not result in model melts depleted enough to explain the

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35 observed seamount data (Fig. 2 10). In addition, HREE/MREE ratios are higher than those in the seamount lavas. Both the INVERMEL and alphaMELTS melting models indicate that, given normal MOR me lting parameters, the DMM composition of Workman and Hart [2005] is not depleted enough in incompatible elements to produce the most depleted basalts found at the Vance seamount chain. The inability of commonly assumed MOR mantle compositions to reproduce the range of incompatible trace element contents in the Vance seamount basalts suggests either DMM is melting to a greater extent than predicted by the model (i.e. the melting temperature is higher than expected) or that the off axis source is inhomogeneou s, likely containing a component that is even more depleted than DDMM. Variations in the trace element ratio (Sm/Yb) N provide more clues to what may be happening in the off axis environment. The slight depletion in the HREE relative to MREE ((Sm/Yb) N is hi gher than predicted by the melting models) in the Vance seamount lavas (Fig. 2 10) could be due to the influence of residual garnet in the source. Researchers have suggested that there is evidence for garnet field melting in the source of ridge MORB [e.g. Salters and Hart, 1989]. However, the higher (Sm/Yb) N values in seamount lavas in comparison to ridge lavas suggests that garnet is playing a more important role off axis. Higher (Sm/Yb) N values could be created in a number of ways. One solution is to hav e a greater degree of melting occur in the garnet field off axis (i.e. deeper melt initiation) in comparison to the melting occurring underneath ridges. Deeper initiation of melting could be caused by a number of factors. Increased

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36 H 2 O in the source can le ad to deeper melting, but similarly depleted basalts from the near axis Lamont Seamounts on the EPR have been shown to have H 2 O contents lower than typical MORB [Danyushevsky, 2001], thus making this scenario unlikely in this case. Increased temperatures at depth can also initiate deeper melting. Typical estimates of potential temperature for MORB mantle are ~1300 1400 C, while as much as 235 C higher [Putirka, 2005; Herz berg et al., 2007; Herzberg and Asimow, 2008]. There is clear evidence for higher temperature melting at the Cobb hotspot and Axial Seamount (just north and west of the Vance segment) [Desonie and Duncan, 1990; Chadwick et al., 2005]. A thermal anomaly ben eath the Vance seamounts could provide the higher temperatures required to remelt residual mantle that has spread laterally from the ridge. Geshi et al. [2007] suggested this process could explain the most depleted basalts recovered from an off axis lava f ield at the EPR. The large size/volume and spatial relationships of the seamounts [Hammond, 1997] is also consistent with the hypothesis that a fixed thermal anomaly exists or did exist beneath the Vance chain. Deeper melt initiation is not the only way t o produce high MREE/HREE ratios. A garnet signature can also be produced by melting a source that is composed of the two lithologies peridotite and eclogite or pyroxenite [Allgre and Turcotte, 1986; Salters and Dick, 2002; Stracke and Bourdon, 2009]. Part ially melting garnet eclogite or garnet pyroxenite could produce high MREE/HREE ratios, thus explaining the garnet signature at the Vance seamount chain without having to invoke a thermal anomaly. Multi

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37 component melting and mixing at the Vance seamount ch ain also is supported by the heterogeneous trace element and isotopic signatures found in Vance samples. This hypothesis has been used to explain the variable chemistry of other off axis lavas by Niu et al. [2002] and Niu and Batiza [1997] who argued that the chemical variability of seamount lavas near the EPR can be explained by melting of a two component mantle (small enriched heterogeneities embedded in a depleted matrix) coupled with subsequent mixing of the melts A two component mantle source has als o been used to explain the variable chemistry found at Davidson Seamount [Castillo et al., 2010], Southwest seamount and Heck seamount chain [Cousens et al., 1995], the Lamont seamount chain [Fornari et al., 1988a,b; Allan et al.,1989], and off axis volcan ism along the EPR [Geshi et al., 2007]. The influence of a two component mantle source on the chemistry of regional JdFR lavas will be explored further in Chapter 3. The Effect of Ridge Migration on Mantle Melting Fractional crystallization and melting mod els indicate that lavas from the Vance seamount chain are being formed by processes more complicated than simple melting and subsequent fractional crystallization of DMM derived melts. Because there are noticeable variations in the chemistry of basalt from the seamounts as they get younger and closer to the ridge, we believe that the amount of melting and/or the source composition is changing as the JdFR ridge migrates to the west and the seamounts get younger due to ridge spreading (the ridge is spreading at a rate ~24.9 km/Ma [DeMets et al., 2010] and is migrating to the west at a rate of ~20.1 km/Ma [Gripp and Gordon, 2002]) One of the simplest models to explain the variable chemistry of the Vance seamount chain is that they are formed from melts generat ed at the edge of the normal ridge melting regime (Fig. 2 11) We hypothesize that these melts are brought to the

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38 surface off axis before they can be mixed in with MORB melts from the larger melting regime. If this model is correct, as the ridge migrates c loser to the seamount chain (due to ridge migration) the height of th is off axis melting region should increase (thus increasing maximum F), causing melts to become more depleted with time if the source of the seamount melts is stationary (a similar model was suggested by Davis and Karsten [1986]). This is consistent with the progressive depletion in LREEs from Seamount A to C, but does not readily explain the re enrichment trend from Seamount E to G. We suggest that normal MORB melts could become more imp ortant in this system as the ridge migrates closer to the seamount chain, thus explaining why the younger seamounts are comprised of basalts with chemical characteristics that look progressively more similar to N MORB as they form closer to Vance ridge seg ment axis. Summary Basalts from the Vance seamount chain are heterogeneous, as evidenced by variations in major and trace element concentrations and isotopic ratios. The Vance chain hosts some of the most enriched and some of the most depleted basalts alon g the JdFR. Trace element and isotopic ratios reveal that the enriched component is most similar to Axial seamount and the Cobb Eickelberg chain, while the more depleted samples found at Seamount C and F are unlike any MORB from the JdFR. Their composition s cannot be explained by melting of typical depleted mantle (DMM). It is likely that the depleted lavas formed from a source that is more depleted than DMM and is isotopically similar to Rogue seamount. The presence of a thermal anomaly in the near axis en vironment is required to generate relatively large degrees of melting. The change in geochemistry as the seamounts get younger was likely influenced by the migration of the ridge. The progressive depletion in incompatible elements in lavas from

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39 the three o ldest seamounts is consistent with the migration of the ridge closer to the source of the Vance seamount chain. Re enrichment in incompatible elements in lavas from the younger seamounts is likely caused by the increasing influence of normal MORB melts as the ridge migrates closer to the seamount source.

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40 Figure 2 1. Location maps of t he Vance seamount chain located at ~45 N at the JdFR on the Pacific plate, northwest of the Vance ridge segment. Other important areas in the JdFR region referred to in t his study include the Cleft segment, Axial segment Coaxial segment, the Cobb Eickelberg seamount chain and Rogue seamount Precisely located dive tracks from the 2006 research cruise are represented by the black lines on the second map. First image creat ed from GeoMapApp. Second image is bathymetric map provided by Monterey Bay Aquarium Research Institute (MBARI)

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41 Figure 2 2 Major element compositions of Vance seamount basalts in comparison to regional JdF R basalt s [Smith et al., 1994; Stakes et a l., 2006] Dashed field within the larger shaded Axial ridge segment basalt field represents where most of the Axial samples plot Within the Vance seamount chain, decreasing Al 2 O 3 and CaO with decreasing MgO and increasing TiO 2 Na 2 O, SiO 2 and K 2 O are co nsistent with crystal fractionation of olivine and plagioclase. Many Seamount B sample s and some Seamount F sample s have anomalously high Al 2 O 3 concentrations, as well as higher Na 2 O, TiO 2 and CaO/Al 2 O 3 and lower CaO, SiO 2 Seamount A has noticeably highe r concentrations of K 2 O, indicative of more enriched compositions. Overall, major element trends indicate that Vance seamount basalts are more diverse and s ometimes more primitive than basalt s erupted at the ridge axis

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42 Figure 2 2. Continued

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43 Fi gure 2 3 Mg O concentration versus selected trace elements. Trace elements generally follow fractionation trends when plotted against MgO concentration. Compatible elements such as Ni and Cr decrease with decreasing MgO content, while incompatible elements like Rb, Sr, Zr, Y, La, Ce, Sm, and Yb increase. Vance seamount compositions are more variable than basalt s erupted at the Vance segment. Seamount A has higher concentrations of the most incompatible elements, consistent with its enriched K 2 O signature

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44 Figure 2 3. Continued

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45 Figure 2 4. Chondrite normalized REE and mantle normalized diagrams of Vance seamount basalts and Vance segment basalts. Vance seamount lavas are LREE depleted tholeiites that are generally less enriched in incompatible tra ce elements than Vance ridge segment basalts and they are more heterogeneous. However, Seamount A is moderately enriched in the most incompatible elements. Many of the seamount samples have a slight depletion in the HREEs in comparison to the MREEs, sugges ting that garnet may be in the source. High Al 2 O 3 samples from Seamount B and F have noticeable positive Sr and Eu anomalies

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46 Figure 2 4. Continued

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47 Figure 2 5 Trace element variation s in Vance seamount basalts in comparison to regional basalts Trac e element compositions for the Cleft segment from Smith et al. [1994] and Stakes et al. [2006]. Axial segment field from Chadwick et al. [2005]. Cobb Eickelberg seamount chain field from Desonie and Duncan [1990]. Rogue field from Chapter 3. Most Vance sam ples have lower concentrations of Y, Zr, Sr, and other incompatible trace elements in comparison to Vance segment basalt s, whereas Seamount A has higher concentrations. This heterogeneity is also reflected in trace element ratios such as Zr/Y, (La/Sm) N (C e/Yb) N and (Sm/Yb) N Regionally, Vance seamount sample s have some of the most depleted as well as some of the most enriched compositions found along the southern JdFR. The large range in trace element ratios suggests that mixing of multiple sources could be an important factor in their formation. Some sample s have (Sm/Yb) N ratios >1, suggesting the influence of garnet in the source

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48 Figure 2 6. Selected Vance seamount major element and trace element compositions and isotopic ratios versus distance fr om the ridge. Circles represent average seamount compositions with 2 variation. The chemistry of the Vance seamount chain changes as the seamounts get younger and thus closer to the ridge. S eamount compositions range to more primitive MgO concentrations t han MORB from the adjacent ridge From Seamount A (the oldest seamount) to Seamount C, K 2 O, Sr, Zr/Y, and (La/Sm) N decrease. From Seamount E to G, these values increase, becoming progressively more similar to ridge lavas. In general, Nd progressively incr eases from Seamount A to Seamount F, while 206 Pb/ 204 Pb progressively decreases. Seamount G compositions are more similar to those from the ridge crest Trends in 87 Sr/ 86 Sr are less obvious and could be obscured by seawater contamination.

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49

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50 Figure 2 7 Variations in Sr, Nd, and Pb isotopic compositions (see Figure 2 5 caption for references). Vance seamount sample s are more isotopically heterogeneous than Vance ridge segment basalts, suggesting that the mantle source for the seamounts is heterogeneous I sotopic ratios of Vance lavas suggest that some lavas were created from a source similar to Rogue (Seamount C and F) while others are more similar to Axial and Cobb Eickelberg lavas (Seamount A and B). Overall, Vance sample s consistently plot between Rogue seamount and Axial/Cobb Eickelberg seamount chain in both trace element and isotopic ratio plots, suggesting that mixing between a depleted source similar to Rogue and a more enriched source similar to Axial/Cobb Eickelberg could be occurring

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51 Figure 2 8. Selected major and trace element results for fractional crystallization models for Vance seamount sample s. Fractional crystallization models were run with Petrolog [Danyushevsky and Plechov, 2011 ] using three different parental magmas at 3 K bars. Over all major element trends are consistent with up to ~50% fractionation of olivine, plagioclase, and small amounts of clinopyroxene. However, trace element trends (especially variations in trace element ratios) cannot be explained by simple fractionation and must be related to melting and/or source compositional variations

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52 Figure 2 9 Model REE inversions for average composition of each seamount [Walters, were created using the average REE composition for each seamount, assumi ng a mantle composition of DMM [Workman and Hart, 2005] and a mantle potential temperature of 1300 C. The melt depth profile for Seamount A has the greatest Dtop (depth where melting ceases), which is consistent with i ts enriched trace element signature. Seamount E and G compositions produced melt depth profiles with increasingly shallower Dtop values. However, the most LREE depleted basalt s from Seamount B and C produced melt depth profiles with Dtop values that are ex tremely shallow, suggesting that melting would have to continue into the base of the crust to produce the most depleted compositions. Melting into crustal depths is highly unlikely, especially off axis, indicating that melting DMM at typical mantle potenti al temperatures will not produce melts depleted enough to match those found at the Vance seamount chain

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53

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54 Figure 2 10 Results of alphaMELTS melting models [Ghiorso et al., 200 2 ; Asimow et al., 200 4 ; Smith and Asimow, 2005; Antoshechkina et al., 201 0]. DMM and DDMM compositions [Workman and Hart, 2005] were used to represent possible depleted mantle compositions. The REE diagram shows the changing composition of model melts as melting progresses in comparison to the chemistry of the Vance seamounts. Neither model can reproduce the most depleted compositions from the Vance seamount chain, even when melting proceeds to the base of the crust. Trace element scatter diagrams also indicate that the only way to produce the most depleted compositions is to me lt depleted mantle to the base of the crust. This is unlikely off axis and is consistent with the results of the REE inversion models

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55 Figure 2 11. Illustration of possible model to explain the variable geochemistry seen at the Vance seamount chain. We assume that ridge migration has moved the ridge axis closer to the stationary point source of melting for the seamount chain over time. Thus, as the seamounts get younger in age and closer to the ridge axis, the height of the melting column underneath the m has increased. This progressive increase in melting could explain the progressive depletion in incompatible elements from Seamount A to C. Ridge migration could also explain the re enrichment trend from Seamount E to G by introducing more normal MORB mel ts as the ridge migrates closer to the seamount chain

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56 CHAPTER 3 THE GEOCHEMISTRY OF BASALTS ERUPTED OFF AXIS ALONG THE JUAN DE FUCA RIDGE: IMPLICAT IONS FOR MANTLE SOUR CE HETEROGENEITY AND MIXING Prior Research on Near Ridge Seamounts With more detailed bathymetric mapping and sampling and the advent of new more precise technologies, researchers have realized that eruptions away from the axis of mid ocean ridges (MOR) are more common than originally thought (e.g. Shen et al. 1993; Goldstein et al 1994, Perfit et al. 1994, Perfit and Chadwick, 1998). Young, off axis eruptions have been documented up to ~80 km away from the ridge [Shen et al., 1993], although most are found between 5 and 15 km from the ridge [Scheirer and Macdonald, 1995; Alexande r and Macdonald, 1996]. Reynolds and Langmuir [2000] suggested that off axis eruptions could account for ~20% of the seafloor around the northern East Pacific Rise (EPR) and Shen et al. [1993] found that the off axis eruptive products represent between 1.5 to 2% of the total volume of the oceanic crust. Off axis eruptive products are commonly found as individual cones, seamounts, seamount chains, or lava flow fields located away from the main ridge axis. The bathymetric expression and chemistry of these sub marine volcanic constructs are unlike those from major hotspot volcanoes. This study will focus on volumetrically important individual seamounts and seamount chains near the ridge axis along the southern Juan de Fuca Ridge (JdFR). Near axis seamounts are commonly more chemically and isotopically heterogeneous than ridge lavas (see Chapter 2) [Graham et al., 1988; Fornari et al., 1988a; Niu and Batiza, 1997; Niu et al., 2002]. For example, Graham et al. [1998] found that the isotopic variability of seamount s off the East Pacific Rise represented ~80% of

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57 the full variability of Pacific MORB Individual seamounts can also host a large degree of variability. Brandl et al. [2012] found that a single seamount adjacent to the northern EPR hosts basalts with the sa me degree of geochemical variability as all documented near axis seamounts. It is hypothesized that off axis lavas are chemically heterogeneous because they do not go through the mixing and homogenizing processes believed to occur at ridge axes [Fornari e t al. 1988a; Leybourne and Van Wagoner, 1991] Consequently, because off axis lavas are less likely to have been significantly modified, they are more likely to reveal the primary characteristics of heterogeneous mantle components and melts, allowing us to investigate mantle melting and source variations that are masked by mixing and fractionation at the ridge axis. Off axis volcanism has not been well studied along the southern Juan de Fuca ridge (JdFR). Work on the Vance and Cobb Eickelberg seamount cha ins (see Chapter 2) [Desonie and Duncan, 1990; Cousens et al., 1995; Chadwick et al., 2005] as well as four individual seamounts [Wendt, 2008] are the only off axis sites that have been studied in detail to date. Here we report new major and trace element as well as isotopic data for individual seamounts found off of both sides of the southern JdFR and discuss their possible sources and petrogenesis. Regional Geology The JdFR is composed of seven segments and is bounded on the south by the Blanco Transfor m and on the north by the Sovanco Transform (Fig. 3 southernmost segment is the Cleft segment, which has a shallow axial high cut by a two to three km wide rift filled with recent lava flows [Carbotte et al., 2006; Stakes et al., 2006]. The lavas are typical N MORB with a limited compositional range and the Cleft

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58 segment is the least geochemically complex of the JdFR segments [Smith et al., 1994]. Directly north of the Cleft segment is the Vance segment, which hosts a much broader, eight km w ide axial valley [Carbotte et al., 2006]. The Vance segment is not as well sampled as the other segments, but limited data from dredges indicate that the Vance segment hosts basalts that are more primitive (higher MgO contents) and more depleted in light r are earth elements (LREE) than lavas erupted at the Cleft segment (see Chapter 2) [Smith et al., 1994]. North of Vance segment is Axial segment, which is noticeably influenced by the Cobb hotspot. This segment is unique in that it hosts a large shield like volcano (Axial volcano) bounded on the north and south by major along axis rift zones [Johnson and Embley, 1990; Embley et al., 1990; Carbotte et al., 2008]. Lavas from Axial seamount, where melt production is higher, are generally more primitive than lav as erupted along the Axial segment rift zones (although some small cones with more primitive lavas have been documented along the rift zones). Axial segment lavas are slightly more enriched in alkalis and highly incompatible elements in comparison to N MOR B erupted at the other segments [Chadwick et al., 2005], although it is important to note that no incompatible element enriched MORB (E MORB) have been documented on axis along the southern JdFR. Coaxial segment overlaps the Axial segment to the north and east and its morphology suggests that it may be influenced by its proximity to the Cobb hotspot to the south (the southern end of the segment is somewhat inflated in comparison to the north end; Sohn et al. [1997]). However, Coaxial basalts show no chemica l effects from the hotspot in that they are generally more incompatible element depleted than MORB from other JdFR ridge

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59 segments [Smith et al., 2011]. Northern Symmetric/Cobb, Endeavor, and West Valley segments are to the north of the Coaxial segment but will not discussed here. There are many off axis features along the JdFR including numerous individual cones/seamounts as well as larger seamount chains (Fig. 3 1). This study compares the chemical characteristics of lavas from the ridge segments to sample s from the Vance seamount chain and the Cobb Eickelberg chain as well as samples from individual seamounts including Rogue, Hacksaw, Jinja, and several unnamed seamounts represented by dive/dredge number (T461, 95DR1, 94DR2, 94DR4, and 94DR5). The Vance se amount chain is located on the Pacific plate to the west of the Vance segment of the JdFR. It is composed of seven edifices that range in composition from extremely depleted to slightly enriched in the most incompatible elements in comparison to Vance ridg e segment lavas (see Chapter 2). To the north of the Vance chain the Cobb Eickelberg seamount chain extends ~550 km to the northwest of Axial Seamount, the current locus of the hotspot centered on the ridge crest [Chadwick et al., 2005]. Basalts from this chain are slightly enriched in incompatible elements compared to ridge basalts, but their isotopic signatures are similar to ridge basalts. Desonie and Duncan [1990] suggested that this indicates that the Cobb hotspot is not a deep seated mantle plume but is a stationary melting anomaly in the upper mantle. Individual seamounts are located off axis on both sides of the JdFR and their locations are shown in Figure 3 1. Several samples were also taken from small cones/edifices off axis (OA) between the Vance segment and the Vance chain ( VSDR5 VS DR14, and VS DR15 termed OA Vance samples in figures).

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60 Methods Initial sample preparation was conducted on ship where samples were described and catalogued and quenched lava rinds were separated for subsequent preparat ion and analysis. Glass fragments from quenched lava rinds were selected for major element, trace element, and isotopic analysis. Glass chips were cleaned in a n H 2 O HCl H 2 O 2 acid mix ture in a sonicator, and the cleanest glass chips (free of phenocrysts, al teration, or Mn oxide crust) were hand picked for analysis using binocular microscope. Glass chips from the rinds of lavas were analyzed for major element concentrations at the USGS (Denver; Colorado) using a JEOL 8900 Electron Microprobe The microprobe was calibrated using USGS mineral standards and nine to ten individual points were analyzed per sample. Full ZAF corrections were applied and analyses were normalized to JdF and the University of Florida in house standard ALV 2392 9 f rom the East Pacific Rise (Smith et al., 2001) Variations in analyses of ALV 2392 9 as well as repeat analysis of previously analyzed glasses during the analytical runs indicate 1 3 % for most elements (T able 2); MnO, K 2 O, and P 2 O 5 have substantially higher error where concentrations are low (< 0.2 wt %). For trace element and isotopic analysis, ~50 mg of hand picked glass chips were leached in 1 mL 2N optima grade HCl + 2 mL 4X H 2 O. 1 mL of optima grade HF + 2 mL of optima grade HNO 3 was then used to dissolved the leached samples (detailed discussions on lab techniques can be found in Goss et al. [2010] and Chapter 2). For trace element and isotopic analysis each sample was analyzed using a multi resolut ion magnetic sector Element2 Inductively Coupled Plasma Mass Spectrometer (ICP MS) at the University of Florida, Department of Geological Sciences after Goss et al. [2010].

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61 Detailed information on data accuracy and reproducibility can be found in Chapter 2 and Goss et al. [2010]. R esults Major Elements Glasses from individual JdFR seamounts Rogue, Hacksaw, Jinja, T461, 95DR1, 94DR2, 94DR4, 94DR5, and seamount VSDR5 were analyzed for major elements and analyses can be found in Appendix C. Other individual s eamount major element compositions (VSDR14/15) were published in Smith et al. [1994]. Overall, except for a few samples from Coaxial segment, basalts from both off axis individual seamounts and seamount chains range to more primitive, higher MgO compositio ns and are not as fractionated as lavas from adjacent ridge segments, except for a few primitive lavas from Coaxial segment (Fig. 3 2; MgO concentrations are as high as 10.06 wt. % for the off axis lavas in comparison to a maximum concentration of ~ 8.5 wt. % for most ridge axis lavas). Off axis basalts also range to very low Na 2 O (minimum 1.64 wt.%) and K 2 O (minimum 0.04 wt.%) concentrations in comparison to ridge basalts. Rogue seamount is comprised of basalts with the greatest range in MgO concentrations (7.45 9.42 wt. %). This seamount also ranges to the lowest TiO 2 Na 2 O, and Al 2 O 3 and the highest CaO and SiO 2 concentrations of all the seamounts. Seamount T461, a small, young cone just west of the Cleft axis, has the most primitive samples with MgO conce ntrations ranging from 9.72 to 10.06 wt. %. The other individual seamounts have basalts that are more evolved than Rogue and T461 and are more similar to seamount chain and ridge axis basalts, with MgO concentrations ranging from 7.03 to 7.76 wt. %. OA Van ce basalts (from off axis cones between the Vance seamount chain and the Vance ridge segment) are also unique because they range to the highest Na 2 O (up to 3.04 wt. %) and K 2 O

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62 (0.05 0.26 wt. %) concentrations of all the individual seamount basalts and are more similar to Vance seamount chain lavas. Trace E lements Trace element concentrations for Rogue, Hacksaw, Jinja, and T461 can be found in Appendix C. Trace element concentrations for the other individual seamounts in this study are from Wendt [2008]. O verall, lavas from individual seamounts are variably LREE depleted tholeiitic basalts (Fig. 3 3; Fig. 3 4). Consistent with other studies of off axis basalts, they are more heterogeneous than lavas erupted at the ridge axis. The overall trace element trend s for off axis basalts cannot be fully explained by fractional crystallization because of the large range in trace element ratios (fractional crystallization will cause individual trace element concentrations to increase, but trace element ratios will rema in unchanged). This range in trace element ratios is more likely to be explained by changes in degree of melting and/or mixing of melts from sources with varying compositions. Rogue seamount is the most depleted in incompatible trace elements of all the of f axis lavas. Overall, Rogue seamount has low trace element ratios, with (La/Sm) N values ranging from 0.35 to 0.57, (Ce/Yb) N values ranging from 0.56 to 0.76, and Zr/Y ranging from 1.30 to 2.15. OA Vance basalts include less LREE depleted samples, which is consistent with their higher Na 2 O and K 2 O concentrations and overall geochemical similarity to more incompatible trace element enriched Vance seamount chain basalts. Trace element ratios support the slightly less depleted signature of the OA Vance basalts with (La/Sm) N values ranging from 0.52 0.82, (Ce/Yb) N values ranging from 0.66 1.12, and Zr/Y values ranging from 2.26 to 3.20.

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63 In terms of incompatible element depletions, basalts from the other individual seamounts in this study lie between those reco vered from Rogue seamount and the OA Vance locations on trace element ratio plots. Hacksaw and 95DR1 samples are more similar to Rogue seamount, with (La/Sm) N values ranging from 0.41 to 0.45, (Ce/Yb) N values ranging from 0.58 to 0.68, and Zr/Y values rang ing from 1.65 to 2.50. The other seamounts (Jinja, T461, 94DR2, 94DR4, and 94DR5) are slightly less depleted, with (La/Sm) N values ranging from 0.52 to 0.62, (Ce/Yb) N values ranging from 0.68 to 0.89, and Zr/Y values ranging from 2.19 to 3.02. Isotopic R a tios Representative basalt samples from Rogue, Hacksaw, T461, and Jinja seamounts were analyzed for Sr Nd Pb isotopic compositions (Appendix C). Overall, off axis basalt s from individual seamounts have a large range in isotopic ratios in comparison to any individual ridge segment (Fig. 3 5) In fact, the diversity in isotopic ratios of all off axis basalt s (including Vance seamount chain and Cobb Eickelberg seamount chain) covers the entire range of isotopic diversity found along the entire southern JdFR. Rogue seamount hosts lavas wi th the least radiogenic Sr and Pb and the most radiogenic Nd, consistent with their trace element depleted signatures ( 87 Sr/ 86 Sr: 0.70207 0.70241; 143 Nd/ 144 Nd: 0 .51324 0.51331 ; 206 Pb/ 204 Pb: 17.93 18.18; 208 Pb/ 204 Pb: 37.30 37.56 ; Fig. 3 5 ). Hacksaw seamount sample s have slightly more radiogenic Sr and Pb and less radiogenic Nd with 87 Sr/ 86 Sr values ranging from 0.70243 to 0.70249 143 Nd/ 144 Nd values ranging from 0.51317 to 0.51319 5 206 Pb/ 204 Pb values ranging from 18.23 to 18.27 and 208 Pb/ 204 Pb values ranging from 37.63 to 37.66. Jinja and T461 seamounts have isotopic signatures the least like Rogue seamount T461 sample s have 87 Sr/ 86 Sr values ranging from 0.7023 1 to 0.7024 7 143 Nd/ 144 Nd

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64 values ranging from 0.5131 6 to 0.51322, 2 06 Pb/ 204 Pb values ranging from 18.40 to 18.41, and a 208 Pb/ 204 Pb value of 37.68. Jinja seamount has 87 Sr / 86 Sr ratios that range from 0.70244 to 0.70256, 143 Nd/ 144 Nd values that range from 0.5130 5 to 0.5131 8 206 Pb/ 204 Pb values that range from 18.47 to 18.4 9, and 208 Pb/ 204 Pb values that range from 37.85 to 37.87. Discussion Mantle Source Characteristics The heterogeneity in major and trace element compositions and isotopic ratios for off axis and on axis basalts from the southern Juan de Fuca ridge area sugg ests that the source for these lavas is heterogeneous, consistent with a similar study of basalts from the northern JdFR from the West Valley along the Endeavor segments and associated near ridge seamounts [Cousens et al., 1995]. The large variations in re lative trace element depletions we have documented in lavas from individual seamounts and seamounts chains over small spatial scales supports the heterogeneous nature of the mantle beneath the southern JdFR. For example, the Vance seamount chain hosts both extremely LREE depleted and slightly LREE enriched basalts (see Chapter 2). The elemental and isotopic data from the southern JdFR are consistent with an hypothesis that these individual seamounts and seamount chains located off axis have been created fro m magmas derived from mantle composed of more than one component. We suggest that the mantle in this region is composed of at least two components: an extremely incompatible element depleted source with low radiogenic Sr and Pb and high radiogenic Nd (simi lar to DMM mantle component) and another more incompatible element enriched source with higher radiogenic Sr and Pb and less radiogenic Nd (similar to HIMU mantle component). Plots of mantle end member isotopic compositions

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65 (defined by Zindler and Hart [19 86]) clearly show that both seamount and JdFR basalts lie on a linear trend between a depleted mantle source (DMM) and an enriched HIMU like mantle source, suggesting that mixing between these two components is occurring (Fig. 3 6). Rogue seamount values a re the most similar to the DMM component, which depleted trace element signature. Jinja, T461, and Hacksaw seamounts have a slightly larger proportion of the HIMU component than Rogue seamount, but these seamounts a re still more similar to the DMM component in comparison to other JdFR lavas found at Cleft, Vance, and Coaxial segments. The Vance seamount chain, Axial volcano, and Cobb Eickelberg lavas have isotopic ratios that reflect the greatest proportion of the HI MU component, consistent with their slightly more enriched incompatible element signatures [Chadwick et al., 2005]. Two component Mantle M elting and M ixing In order to better constrain the magmatic processes that are occurring and the sources that are pr esent along the JdFR, isotopic mixing calculations can be used to investigate the effect of mixing of melts from depleted and enriched seamounts to produce ridge axis compositions. Rogue seamount was chosen as the depleted end member because of its extreme ly depleted trace element and isotopic signature. Mixing lines between the most depleted Rogue basalt and several more enriched basalts from the Vance seamount chain were calculated and the results are shown in Figure 3 7. The spread in isotopic data for s eamounts as well as ridge axis basalts cannot be explained by one mixing line, indicating that melts of slightly different compositions are mixing together to form the basalts erupted along the JdFR. Coaxial segment lavas can be formed by mixing the larges t proportion of depleted melts (75 90% depleted melt component) with more enriched melts. Cleft and Vance segment lavas can be formed

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66 by mixing a smaller proportion of depleted melts with more enriched compositions (40 60% depleted melt component). As dis cussed above, JdFR samples form a mixing line between DMM and HIMU sources on mantle component diagrams. Thus, isotopic and trace element mixing calculations were also used to quantify the relative proportions of these global mantle end members in the JdFR mantle. The DMM component is assumed to be lherzolitic mantle and the associated partial melts from this component are represented by one of the most depleted basalts from Rogue seamount. However, an appropriate lava composition to represent the end membe r HIMU component is not found along the JdFR, because all lavas have at least a partial DMM signature (as seen in Fig. 3 6). The HIMU component is believed to be the remnants of ancient subducted oceanic lithosphere [Zindler and Hart, 1986]. To estimate an acceptable HIMU melt composition, we modeled the trace element composition of small degree batch melts of b ulk dehydrated oceanic crust (compiled from Hanyu et al. [2011] and Stracke and Bourdon [2009]), assuming the HIMU component is lithologically disti nct eclogite [Kogiso and Hirschmann, 2006; Stracke and Bourdon, 2009; Day et al., 2010]. These batch melts were then mixed in varying proportions with the depleted Rogue seamount composition (see Appendix C for model parameters). The mixing models (Fig. 3 8) indicate that a batch melt of ~3% bulk dehydrated oceanic crust best represents the trace element composition of the more enriched HIMU end member (because of its enrichment in the most incompatible elements). Consistent with the basic isotopic mixing c alculations discussed above, no one mixing line can explain the full variation in 87 Sr/ 86 Sr isotopic ratios found in JdFR lavas. Seawater alteration could have caused some samples to

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67 have anomalously high 87 Sr/ 86 Sr ratios. However, all glass samples were l eached before analysis to remove any surficial alteration, suggesting that the samples with higher 87 Sr/ 86 Sr could be actual mantle values. If this is the case, the range in radiogenic Sr found in JdFR lavas can be explained by mixing a depleted DMM melt w ith HIMU melts that have a small range of 87 Sr/ 86 Sr values, represented by the three mixing lines in Figure 3 8. This range is within the defined isotopic variation for the HIMU component [Zindler and Hart, 1986], however, suggesting that a third mantle re servoir is not needed to produce the overall geochemical variation. Mixing of these enriched melts in varying proportions with the depleted Rogue basalt produces a range of compositions that can explain the full geochemical variation documented along the southern JdFR. It is important to note, however, that there are slight discrepancies in the relative proportions of each component between different trace element ratios (Fig. 3 8). For example, Sm/Nd versus Ce/Sm suggests that a maximum of ~6% HIMU is nee ded to produce the most enriched Cobb Eickelberg lavas, whereas other trace element ratios indicate that ~10% HIMU melt is needed. In general, however, the chemistry of m ost individual seamounts can be explained by mixing between 1% and 4% HIMU melt with d epleted Rogue basalt, consistent with the relatively depleted trace element signature of the seamounts lavas from the Cleft and Vance segments need a higher proportion of HIMU mel t (up to 6%) than the off axis seamounts while a smal ler proportion of HIMU melt (~3 %) is needed to produce the trace element and isotopic signatures of the more depleted Coaxial segment Axial segment/Cobb Eickelberg seamount chain compositions can be modeled using the greatest proportion of HIMU melt (up to ~10% ), while the Vance

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68 seamount chain has compositions with the largest variation, with HIMU melt proportions ranging from ~1% to ~10 %. Origins of JdF R M antle C omponents The fact that lavas erupted at off axis seamounts adjacent to the JdFR are general ly more chemically heterogeneous than those erupted at the ridge crest is consistent with the hypothesis that they have not undergone as much mixing and homogenization prior to eruption. Hence basalt s from these off axis areas can be used to investigate variability in mantle source chemistry in the southern JdF R region that are not reflected in ridge axis lavas. Inspection of the latitudinal compositional variations of off axis samples ( Fi g. 3 9) reveals some important spatial changes In the south ern mos t portion of the JdFR off axis volcanism produces LREE depleted N MORB and lave compositions are fairly homogeneous. However, at the latitude of the Vance seamount chain, a noticeable fluctuation in chemistry occurs. Minimum Zr/Y values become progressive ly lower ( more depleted ) moving north through the southern (youngest) portion of the Vance seamount chain. It is important to note that the trend in (La/Sm) N is harder to determine. However, for the three youngest seamounts, average (La/Sm) N values progres sively decrease moving north (as the seamounts get older; see Chapter 2) 143 Nd/ 144 Nd ratios also decrease moving north while Pb isotopic ratios decrease. The increasingly more trace element and isotopic depleted signature in the southern portion of the V ance seamount chain is likely caused by the waning influence of ridge axis melts as the seamounts get older and farther away from the ridge (see Chapter 2), thus indicating that this change in chemistry is not only spatial but also temporal.

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69 In the northe rn portion of the Vance seamount chain, which is comprised of the oldest seamounts samples progressively become more trace element and isotopically enriched and this enrichment trend continues through the A xial segment The similarity in trace element an d isotopic signatures between the oldest and most enriched basalts from the Vance seamount chain and basalts from Axial seamount and the Cobb Eickelberg seamount chain indicate that these lavas may have obtained their enriched signature from the same sourc es that fed the Cobb hotspot. Chadwick et al. [2005] studied lavas from Axial volcano and the adjacent Axial rift zones and found that the Cobb hotspot had a declining and yet significant effect on lava chemistry all the way to the north and south ends of could also influence other nearby locations such as the Vance seamount chain and other nearby individual seamounts. To the north of A xial segment, both Coaxial segment lavas and Rogue seamount la vas are more trace element and isotopically depleted (more depleted than anywhere else in the region). The cause of this extreme depletion signature is enigmatic. The simple alphaMELTS melting model described in detail in Chapter 2 was compared to the che mistry of Rogue seamount (Fig. 3 10). This melting model produces a melt composition (integrated from instantaneous melt compositions over the melting region) from a depleted MORB mantle source (DMM composition of Workman and Hart [2005]) under temperature s and pressures expected to cause normal melting at the Vance ridge segment. The comparison of this aggregate melt composition to Rogue seamount basalts reveals that, similar to the model developed for the Vance seamount chain, melting of typical depleted mantle at normal ridge temperatures and pressures does not

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70 produce melts that are depleted enough to represent Rogue samples. Geshi et al. [2007] and Cousens et al. [1995] suggested that extremely depleted off axis lavas they documented along the EPR could be explained by remelting of mantle that had already been melted at the nearby ridge. If this is the case for Rogue seamount, the isotopic ratios for these lavas should be similar to the adjacent Coaxial segment, even though the trace element signature is more depleted. However, as seen in Figure 3 11, isotopic ratios correlate with trace element ratios, with Rogue seamount in general having less radiogenic Pb than Coaxial segment. There could be two reasons for this. Wendt et al. [1999] hypothesized that melting of two component mantle would preferentially remove any enriched heterogeneities at the ridge. Any remelting of this material off axis would then be missing the enriched trace element and isotopic component, leaving off axis lavas with more deplete d trace element and isotopic signatures. Hence, the correlation of JdFR seamount trace element compositions with Sr Nd Pb isotopic ratios could be more evidence for a two component source for JdFR lavas. Another explanation for this trend is simply that t he geochemistry of Rogue seamount basalt s could actually be a long term mantle depletion signature (i.e. the Rogue mantle source was not depleted recently, but anciently) If Rogue seamount does represent the depleted component in the JdFR mantle with lit tle to no contamination from the more enriched mantle component, isotopic ratios from Rogue seamount can be used to calculate a model age for this reservoir. The Pb Pb isochron for Rogue seamount yielded an age of ~3.1 Ga (Pb Pb isochron ages were also cal culated for the other JdFR lavas, but, because these are likely affected by mixing of melts with different isotopic ratios, these ages likely have little meaning; calculated

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71 slopes and associated ages are presented in Figure 3 12). The fact that Rogue seam ount basalts yield a 3 billion year old age supports the idea that the Rogue mantle source could have been anciently depleted, thus explaining the correlation between isotopic and trace element ratios. Summary Basalts from near axis seamounts along the s outhern JdFR are geochemically heterogeneous in comparison to basalts erupted along the ridge axis. Homogenization of melts along fast and intermediate spreading rate ridges masks the true diversity of mantle melt compositions formed in the sub axial envi ronment. The diverse seamount basalt compositions and represent melts that ultimately were derived from varying proportions of a two component mantle. Rogue seamount is the most LREE depleted seamount thus far analyzed along the JdFR and best represents th e more depleted mantle component. Melting of typical DMM [Workman and Hart, 2005] cannot produce melts depleted enough to explain the chemistry of Rogue lavas, suggesting that either the mantle source for Rogue seamount was previously partially melted or t hat it is more long term depleted than the source for ridge mantle. Isotopic trends indicate that the more enriched mantle component is best represented by the HIMU end member. Variable extents of mixing of melts from these two end members can explain the full range in geochemical variation seen at the JdFR.

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72 Figure 3 1. Location map showing study areas off axis volcanism along the Juan de Fuca Ridge (JdFR). The JdFR extends from ~44.5 N, 130.4 W to ~48.9 N, 128.8 W and is bounded on the south by the Blanco Transform and on the north by the Sovanco Transform. It is composed of seven segments and the southernmost four segments will be focused on in this paper: Cleft segment, Vance segment, Axial segment, and Cobb Eickelberg segment. There are many off axis features along the southern JdFR, including the Vance and Cobb Eickelberg seamount chains, as well as individual seamounts scattered off both sides of the ridge, including nine seamounts focused on is this study

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73 Figure 3 2. M ajor element com position al variations of individual seamount basalt s in comparison to larger off axis seamount chains and ridge lavas. Cleft segment data are from Stakes et al. [2006]. Vance segment and Vance seamount chain data are from Chapter 2. Axial segment data are from Chadwick et al. [2005], Coaxial segment data are from Smith et al. [ 2011 ] and Cobb Eickelberg seamount chain data are from Desonie and Duncan [ 1990 ] Overall, individual seamount glasses have a range in MgO compositions that cover much of the variati on seen in other off axis and on axis regions along the JdFR. In particular, Rogue seamount has consistently unique major element concentrations in comparison to other JdFR basalts. OA Vance samples have higher K 2 O and lower FeO T values than other individu al seamounts and are more similar to some samples from the Vance and Cobb Eickelberg seamount chains. Except for a few lavas from Coaxial segment, off axis volcanism ranges to more primitive values (higher MgO concentrations) than ridge basalts and also ha s more variable compositions for the other major elements

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74

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75 Figure 3 3 Trace element ratio plots of off axis seamount basalt s in comparison to ridge basalts erupted along the JdFR. Cleft, Vance, Axial, Coaxial, Cobb Eickelberg data from refe rences listed in Figure 1. DR1, 2, 4, and 5 seamount data are from Wendt [ 200 8] Individual seamounts range from extremely low incompatible trace element concentrations (e.g. Ce, Ba, Sr) and ratios (e.g. (Ce/Yb) N (La/Sm) N Zr/Y) best represented by Rogue seamount basalt s to trace element values that are slightly more enriched than ridge lavas and are similar to Vance and Cobb E ickelberg lavas (OA Vance lavas ). Only some of the trace element variation can be explained by fractional crystallization. The ove rall positively sloped trace element trends for southern JdFR lavas suggests that melting variations and/or mixing of melts from multiple sources is controlling most of the trace element variation for lavas from this region

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76 Figure 3 4. Chondrite norm alized REE and primitive mantle normalized diagrams of individual seamount sample s in comparison to the Vance seamount chain (hosts the largest range of geochemical variation in the region; see Chapter 2 ). Individual seamount basalt s are LREE depleted thol eiites that are generally less enriched in incompatible trace elements than ridge basalts and they are more heterogeneous. OA Vance lavas are slightly less depleted in incompatible elements than the other individual seamounts and are similar to the most en riched basalt s from the Vance seamount chain. Rogue seamount hosts the most depleted basalt s thus far analyzed along the JdFR

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77 Figure 3 5. Variations in Sr, Nd, and Pb isotope compositions for individual seamounts in comparison to Vance and Cobb Eickel berg seamount chains and on axis lavas. Cleft, Vance, Axial, Coaxial, Cobb Eickelberg data from references listed in Figure 1 The variability in isotopic compositions for basalts erupted on and off axis suggests that the mantle source for the seamounts i s relatively heterogeneous. Regionally, isotopic values range between Rogue seamount and Axial/Cobb Eickelberg seamount chain. The range in isotopic ratios found in the sample s along the JdFR suggests the mantle source for these lavas is composed of at lea st two components, a depleted source similar to Rogue and a more enriched source similar to Axial/Cobb Eickelberg

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78 Figure 3 6. Selected isotopic ratios of JdFR lavas in comparison to mantle end member compositions defined by Zindler and Hart [1984]. On all diagrams, Rogue seamount is the most similar to the DMM end member and the rest of the lavas form a generally linear mixing trend toward the HIMU end member. Axial segment/Cobb Eickelberg seamount chain and the Vance seamount chain are the most sim ilar to the HIMU component, while the other JdFR lavas are more similar to DMM. Plots adapted from Cornejo, E. A. (2008), Isotope geochemistry of basaltic glasses from the Vance seamounts, a near ridge seamount chain adjacent to the Juan de Fuca Ridge, mas ter's thesis, Carleton Univ., Ottawa

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79 Figure 3 seamount chain. No one mixing line can explain the full range in isotopic data, indicating that JdFR lavas were formed by mixing of end member melts with small variations in isotopic signatures. The isotopic chemistry of most ridge axis basalts can be produced by mixing between 40% and 60% of the deple ted melt with the more enriched melts. Coaxial segment basalts, however, can be produced by a larger proportion of the depleted melt (75 90%), consistent with their LREE depleted signature

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80 Figure 3 8. Isotopic and trace element mixing models. Ca lculated mixing percents are between melts from a depleted mantle source (DMM) represented by Rogue seamount basalts and melts from an enriched source represented by a model 3% batch melt of dehydrated oceanic lithosphere (HIMU component; see Table 4). Whe n comparing JdFR samples to calculated trace element ratios to determine the relative proportions of each mantle component in lavas from this region, there are slight discrepancies between different trace element ratios (see text for more discussion). Mixi ng models indicate that Rogue seamount has the lowest proportion of the HIMU component (maximum ~1%). Most individual seamounts can be explained by adding between 1% and 4% HIMU to the depleted Rogue source. Cleft and Vance segment lavas have a slightly hi gher proportion of the HIMU component (up to 6%), while Coaxial segment has a much smaller proportion (~3%). Axial segment/Cobb Eickelberg seamount chain has the larger proportion of HIMU with a maximum proportion of ~10%. Vance seamount chain has composit ions with the largest variation, with proportions ranging from ~1% to ~10%

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81 Figure 3 9. Selected trace element and isotopic ratios versus latitude for off axis basalts and Axial segment (influenced by Cobb hotspot: Chadwick et al. [2005]. In the most sout hern parts of the JdFR, trace element and isotopic ratios are fairly constant. However, beginning near the latitude of Hacksaw seamount and the Vance seamount chain, the chemistry of off axis volcanism becomes more depleted (also less radiogenic Pb and mor e radiogenic Nd). In the older part of the Vance chain, lavas become more enriched and are more similar to Axial lavas. At Rogue seamount compositions become significantly more depleted and have lower concentrations of radiogenic Pb and higher concentratio ns of radiogenic Nd. The abrupt change in composition from Axial segment to Rogue seamount suggests that the mantle underneath these two regions of the JdFR is significantly different

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82

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83 Figure 3 10. Results of alphaMELTS melting model from Chapter 2 in comparison to most incompatible element depleted Rogue seamount basalts. The model composition represents the average composition of aggregated melts from DMM at the base of the crust (DMM composition from Workman and Hart [2005]) under typical MOR m elting conditions (see Chapter 2 for detailed discussion on modeling methods). The melting model cannot reproduce the most depleted basalts from Rogue seamount, even when melting proceeds to the base of the crust. This suggests that the source for Rogue se amount is more depleted than the composition of mantle that is typically believed to be the source of MORB

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84 Figure 3 11. Variations in 206 Pb/ 204 Pb versus several incompatible element ratios. In general, incompatible element ratios correla te with isotopic ratios. Rogue seamount has the lowest 206 Pb/ 204 Pb ratios and the lowest incompatible element ratios. This correlation suggests that either the more enriched component in the mantle source has been removed by prior melting or that the sourc e for Rogue seamount is long term depleted

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85 Figure 3 12. 206 Pb/ 204 Pb versus 207 Pb/ 204 Pb showing calculated ages for Pb Pb arrays for selected JdFR ridge segments and off axis seamounts. Rogue samples (the least likely to be affected by mixing) pro duce a model age of ~3.1 Ga, suggesting that the source for this seamount could be long term depleted. Calculated ages for other seamounts and ridge segments range from 1.3 to 2.8 Ga. However, these ages are likely meaningless if these lavas were formed du e to mixing of melts with different isotopic ratios. These ages can tell us that the enriched component is younger than the more depleted component because the ages are younger than the Rogue seamount model age

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86 CHAPTER 4 THE LAMONT SEAMOUN TS REVISITED: GEOCHE MICAL SIGNATURES OF MANTLE SOURCES AND M ELTING PROCESSES AND CRUSTAL ASSIMILATION PROCESSES A Review of the Lamont Seamount Chain The first near ridge seamount chain to be studied in detail was the Lamont seamount chain located at ~10 N East Pacific Rise (EPR) (Fig. 4 1) [Allan et al., 1988; Fornari et al., 1988a, b; Allan et al., 1989]. These studies revealed that the lavas from these seamounts were characteristically more primitive (higher MgO concentrations) and more geochemically heterogeneous than basalts erupted at the adjacent EPR. The study of the Lamont seamounts has highlighted the importance of near ridge seamounts in the study of mantle melting processes and source variations because their geochemistry suggests that they ha ve not been substantially homogenized at ridge centered magma chambers, thus being more likely to reflect mantle chemical signatures. Subsequent studies of other near ridge seamounts (see Chapter 2 and 3 from this study) [Leybourne and Van Wagoner, 1991; C lague et al., 2000] have revealed similar geochemical characteristics and trends. Since the original studies of the Lamont seamount chain, geochemical analysis has become more robust with the advent of new technologies. Furthermore, we have a much more com plete and comprehensive view of the composition of EPR lavas and the processes involved in generating them (e.g. Perfit et al. [1994]; Batiza and Niu [1997]; Sims et al. [2002]; Goss et al. [2010]). With this in mind, we have reanalyzed many of the Lamont seamount chain samples reported in the above studies for a full suite of trace elements and Sr Nd Pb isotopic ratios to better constrain the sources and magmatic processes that formed these seamounts and to help understand mid ocean ridge magmatism in gene ral.

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87 Background Seamount chains are commonly found in close vicinity to mid ocean ridges and, unlike ocean island chains found in the middle of oceanic plates, are believed to be related to the melting regime associated with the overall ridge system. Ther e are two types of near ridge seamounts: those aligned along relative plate motions and those aligned along absolute plate motions. Seamount chains formed due to absolute plate motion get progressively older farther away from the ridge. However, young lava s can be found along the entire length of a seamount chain associated with relative plate m otions [Batiza et al., 1990] Near ridge seamounts commonly have a morphology consisting of a round edifice with flat summits that host breached calderas [ Clague et al., 2000], suggesting the presence of large magma chambers However, there is considerable debate about how important magma chambers are underneath near ridge seamounts. Leybourne and Van Wagoner (1991) used mineralogical information (phenocrysts lack zon ing, have equilibrium compositions, and crystallized at high temperatures) as well as the primitive nature of the Heck and Heckle seamount basalts to infer that magma chambers are not important in the formation of these lavas. In contrast, Clague et al. [2 000] suggested that near ridge seamount magma chambers could exist, but that magmas pass through the chambers quickly. This would still produce hot, primitive lavas that lack significant mineral zoning and would also explain the presence of the calderas. A s time progresses, these magma conduits migrate as spreading at the axis proceeds, cre ating multiple nested calderas [Fornari et al., 1988b] Prior Research The Lamont seamount chain consists of five volcanoes terminating in a set of small cones adjacent to the ridge axis (Fig. 4 1) These volcanoes are 800 1400 m high

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88 with volumes ranging from 25 to 120 km 3 and are encircl ed by smaller lava cones 50 200 m high [Allan et al., 1989] The chain is built on young crust 0.1 0.7 Ma old [Allan et al., 1989] and excepting Sasha seamount, each volcano has a summit calde ra [Fornari et al., 1984] The seamounts appear to get progressively older with distance from the EPR [Barone and Ryan, 1990] although each seamount has evidence of relatively young looking volcan ism [ Fornari et al., 1988b] The magma budget has likely lessened through time and each eruptive episode was separated by a period of inactivity lasting ~0.04 Ma. [Barone and Ryan, 1990] Lamont seamount basalts have a simple mineralogy usually comprised of only plagioclase and olivine with accessory Cr rich spinel [ Fornari et al, 1988a; Allan et al., 1989] Most plagioclase and olivine exhibit only slight reverse or norma l zoning between 1 and 2 mol %, although some samples contain a bimodal population of plagioclase, including some high An compositions [ Fornari e t al., 1988a; Allan et al., 1988] Clinopyroxene is only found as microphenocrysts in the most evolved samples, indicating that crystallization occurred at moderate to low pressures and most lavas were not evolved enoug h to crystallize clinopyroxene [Fornari et al., 1988a] Original geochemical studies of Lamont seamount basalts found that they are LREE depleted tholeiites that have a r ange of primitive major element compositions (Fig. 4 2) [ Fornar i e t al., 1988a; Allan et al., 1989] Enriched MORB and alkali rocks, which have been found at some other near axis seamounts [Niu and Batiza, 1997; Niu et al., 2002] were not documented in this chain [Fornari et al., 1988a] The original studies found th at t he Lamont seamount basalts are generally more depleted in incompatible elements than associated ridge basalts, have less radiogenic Sr and m ore radiogenic Nd

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89 compositions, h ave a larger range of Pb isotope compositions, thus making them more geochemica lly heterogeneous [Fornari et al., 1988a,b; Allan et al., 1989] This study presents the results of trace element and isotopic reanalysis using ICP MS for Lamont samples investigated in the above studies. Methods Glass fragments from quenched lava rinds w ere selected for trace element and isotopic re analysis based on sample availability. Samples were chosen to best represent the geochemical variability documented in the Lamont seamounts in prior studies. Glass chips were cleaned and hand picked under a bi nocular microscope for analysis. For trace element and isotopic analysis, ~50 mg of hand picked glass chips were leached in a 2N HCl:4X H 2 O mixture to remove any seawater alteration and/or Fe Mg contamination. Each sample was analyzed for trace element an d isotopic ratios using a multi resolution magnetic sector Element2 Inductively Coupled Plasma Mass Spectrometer (ICP MS) at the University of Florida, Department of Geological Sciences More detailed methods, instrumental calibration, and long term reprod ucibility can be found the works of Chapter 2 and Goss et al. [2010]. Glasses from Lamont seamount lavas were originally analyzed by Allan et al. [1989] for trace elements using XRF and INAA techniques and for Sr Nd Pb isotopic ratios using TIMS (samples were not leached prior to analysis). We reanalyzed 37 samples (samples chosen to best represent the geochemical variability documented in the Lamont seamount chain) for trace elements using ICP MS and 17 samples for Sr Nd Pb isotopic ratios using MC ICP M S (see Appendix D for full data set). The results of this study were compared to the values published in 1988. In general, concentrations

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90 for many elements (Zr, Y, Ni, Co, Sc, Zr, Rb) were slightly lower than values produced by the XRF/INAA methods of Alla n et al. [1988] (Fig. 3). However, both methods produced similar concentrations (% difference between analyses <5%) for some elements (Sr, Yb, Sm, Ce, La). Because of the good reproducibility for these elements, concentrations of these elements from Allan et al. [1989] in samples that were not reanalyzed (because of lack of adequate sample) were used in plots for this study. Isotopic ratios published by Fornari et al. [1988a] are significantly different from our results. In particular, 87 Sr/ 86 Sr and Pb is otopic values are higher and 143 Nd/ 144 Nd isotopic ratios are lower in comparison to our reanalysis (Fig. 4 3). This is likely due to the fact that the Lamont glasses were not sufficiently leached by Fornari et al. [1988a] (making seawater contamination mor e likely, thus causing higher 87 Sr/ 86 Sr and Pb isotopic values [McDonough and Chauvel, 1991]). Results Trace Elements Selected reanalyzed trace element abundances and general trends presented in Figure 4 4 show decreasing compatible element concentration s and increasing incompatible element concentrations with decreasing MgO concentrations (consistent with fractionation of olivine and plagioclase). Most basalts from the Lamont seamount chain are more light rare earth element (LREE) depleted than basalts e rupted at the nearby EPR. For example, Lamont samples range to lower (La/Sm) N (Ce/Yb) N and Zr/Y values (0.23 0.71, 0.43 1.1, 1.80 3.79 respectively; Fig. 4 5) than ridge basalts. This difference is particularly evident on rare earth element (REE) and pri mitive mantle normalized diagrams (Fig. 4 6), where Lamont seamount basalts are almost exclusively more depleted in LREE and the most incompatible elements (e.g. Rb, Ba, Th, Nb) in

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91 comparison to EPR axis basalts. The more depleted nature of Lamont basalts is consistent with the lower concentrations of K 2 O in Lamont samples in comparison to ridge lavas (Fig. 4 2) [Allan et al., 1989]. Slight depletions in heavy REE relative to middle REE (Sm/Yb) N = 0.88 to 1.31) has been used to suggest that some mantle melt ing may have occurred in the garnet field [Sobolev, 1996; Shimizu, 1998]. In general, REE patterns for Lamont basalts are smooth. However, some samples have slightly elevated concentrations in some incompatible trace elements, most noticeably the LREE, and Sr. Sr concentrations are as high as 194 ppm in comparison to more typical Lamont seamount concentrations of ~90 ppm and EPR basalts ~ 110 ppm (Fig. 4 4). On REE and primitive mantle normalized diagrams (Fig. 4 6), these differences are apparent as large positive Sr anomalies, represented by high Sr/Sr* values (maximum Sr/Sr*: 1.41) and an elevation in La and Ce normalized concentrations, forming a humped shape in both diagrams. These high Sr basalts also have high concentrations of Al 2 O 3 (up to 17.91 wt. %; Fig. 4 2) and low concentrations of SiO 2 (48.5 49.4 wt. %) and Sc (29.9 36.09 ppm), and some samples in this group have high Na 2 O concentrations (up to 3.35 wt. %). They also have some of the highest Zr/Y values (up to 3.87; Fig. 5) and lowest LIL conce ntrations (Fig. 4 6). Isotopic R atios With the exception of two samples, our reanalysis of Lamont samples indicates that Lamont basalts have fairly homogeneous Sr Nd Pb isotopic compositions (Fig. 4 7). In comparison to EPR axis basalts, Lamont seamount lavas generally have higher 143 Nd/ 144 Nd ratios and lower 87 Sr/ 86 Sr and Pb isotopic ratios. 87 Sr/ 86 Sr for Lamont samples varies from 0.70222 to 0.70252 and 143 Nd/ 144 Nd varies from 0.51320 to 0.513254. 206 Pb/ 204 Pb varies from 17.91 to 18.04, 207 Pb/ 204 Pb vari es from 15.42 to

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92 15.45, and 208 Pb/ 204 Pb varies from 37.24 to 37.42. There are two samples from MOK and Sasha seamount that have lower 143 Nd/ 144 Nd and higher 87 Sr/ 86 Sr and Pb isotopic ratios. Although all samples were leached before analysis, it is possible that seawater and/or Mn precipitation could have contaminated the original isotopic ratios for these two samples. However, because the isotopic values correlate fairly well with trace element ratios (Fig. 4 8) it is possible that these could represent pri mary mantle isotopic values. Discussion Possible Origins of High Al, High Sr Basalts Fornari et al. [1988a,b] and Allan et al. [1989] argued that basalts from the Lamont seamount chain experienced very little magma mixing or crustal assimilation because of the rarity of xenocrysts and the fact that the small number of phenocrysts found in these lavas were unzoned. Allan et al. [1989] proposed that the high Al basalts formed by the fractional crystallization of clinopyroxene at high pressures, but noted th at this model could not explain the enrichment in the light and middle REEs. Others have tried to explain high Al lavas by the suppression of plagioclase fractionation due to high water concentrations [Danyushevsky, 2001]. However, Danyushevsky [2001] anal yzed H 2 O concentrations in Lamont glasses and found that they had lower concentrations than ridge lavas, in agreement with their incompatible element characteristics, confirming that they were not anomalously hydrous. Even when comparing high Al, high Sr s amples to the other Lamont lavas, there is no clear connection between the anomalous compositions and H 2 O concentration. We hypothesize that the anomalous high Al, high Sr basalts found in the Lamont seamount chain may have formed as a result of assimilati on of gabbroic rocks within the

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93 oceanic crust. There is ample evidence for melt rock reaction in gabbros sampled at mid ocean ridges. For example, it has been suggested that disequilibrium clinopyroxenes in gabbros from the Kane Megamullion (Mid Atlantic R idge) were likely formed due to reaction between migrating melts and primitive cumulates [Lissenberg and Dick, 2008; Dick et al., 2010]. There is also evidence for assimilation in ophiolite sequences. For example, Coogan et al. [2002] documented xenoliths of gabbroic and basaltic compositions in the uppermost plutonic sections of the Oman ophiolite. These consistent with progressive assimilation. Wanless et al. [2011] found th at dacites erupted along the 9 N overlapping spreading center of the EPR could be explained by fractional crystallization coupled with assimilation of hydrothermally altered oceanic crust by a parental MORB melt. The genesis of anomalous melt inclusion com positions (ultra depleted in trace elements and high Al 2 O3 and Sr/Sr*) from basalts from the Siqueiros Transform Fault were also explained by assimilation of gabbroic material [Danyushevsky et al., 2003]. Evidence for assimilation in the Lamont lavas is fo und in the geochemical variation of Lamont lava spinels. Allan et al. [1988] argued that some Cr rich spinels found in some Lamont samples that were out of equilibrium with their host glass were likely externally introduced and came from a more evolved and Fe rich source. In fact, sample F3 4 (one of the samples that hosts these Cr rich spinels) is a high Al, high Sr basalt. It is also important to note that some of the high Al samples have a bimodal distribution of plagioclase compositions (one group has v ery high An content and the other group has less [Allan et al., 1989]). Laboratory experiments suggest that high An plagioclase can

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94 be formed as a result of to diffusion reaction processes triggered by the juxtaposition of two plagioclase saturated melts ( simulating a MORB melt juxtaposed with gabbroic wall rock) [Lundstrom and Tepley, 2006]. To investigate the potential geochemical effects of assimilation on MORB lavas, the alphaMELTS program was used to model the effects of assimilation (bulk rock additio n) at constant pressure (2 Kbars) and temperature (1300 C). The effect of gabbro assimilation was modeled on several melt compositions: a model primitive normal MORB (N MORB) composition and several Lamont lavas lacking anomalously high Al 2 O 3 and Sr conce ntrations. It is important to note that determining a likely gabbroic composition for the assimilant in these models is difficult because of the wide range in major and trace element compositions that have been documented for gabbros [ex. Hayman et al., 20 11], as well as the general lack of gabbroic samples analyzed for a full suite of trace elements. Gabbro 95OC25 from the Oman Ophiolite [Macleod and Yao, 2000] was chosen as the starting gabbro composition because there is a full major and trace element da ta set available for this sample and the gabbro is a typical LIL and REE depleted oceanic plutonic rock. Assimilation of this gabbroic material into a typical primitive N MORB composition (~14 wt. % MgO) results in higher Al 2 O 3 and CaO concentrations and lower MgO concentrations (Fig. 4 9). However, fractional crystallization (using Petrolog; [Danyushevsky and Plechov, 2011]) of this mafic hybrid melt composition does not result in high enough Al 2 O 3 concentrations at lower MgO values because plagioclase e nters the liquidus at ~10 wt. % MgO. This suggests that anomalously high Al 2 O 3 concentrations at lower MgO might form from melts with lower MgO concentrations by

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95 partially assimilating gabbro as they migrate and evolve in the lower crust. Fractional crysta llization of these more evolved magmas potentially could produce the heat needed (latent heat of crystallization) to assimilate the surrounding gabbroic material [Spera and Bohrson, 2001]. Gabbro assimilation calculations using three more evolved Lamont ba salts (8.5 10 wt.% MgO) produce trends similar to those exhibited by the high Al samples (higher Al 2 O 3 lower CaO/Al 2 O 3 SiO 2 ) but also generated higher CaO concentrations, unlike the relatively low CaO contents in the high Al, high Sr lavas. One drawback of the alphaMELTS program is that only bulk compositions can be assimilated. Trace element melting calculations were performed to investigate the effect of the assimilation and mixing of non modal gabbro melts on the trace element depleted Lamont lavas. S ource trace element compositions are from the Oman gabbro discussed above and this gabbro was assumed to have 20% olivine, 30% clinopyroxene, and 50% plagioclase modal phase percentages (no actual modal percentages for this sample were published, and melti ng/mixing calculations using calculated normative mineralogy did not reproduce the trace element trends for the high Al, high Sr basalts). Melting was assumed to be batch non modal melting, with clinopyroxene and plagioclase melting in proportion to their relative modal percentages (37.5% clinopyroxene, 62.5% plagioclase). Crystal melt partition coefficients used to calculate trace element abundances were taken from the compilation of Wanless et al. [2012]. The calculations indicate that as partial melting of the gabbro composition increases, incompatible trace element concentrations decrease in the partial melt. (Fig. 4 9). However, Sr/Sr* increases with extent of melting, suggesting that this value can be used as an indicator of degree of assimilation of

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96 gabbro. A range of gabbro partial melt compositions was chosen to mix with the most incompatible trace element depleted Lamont seamount composition (because many of the anomalous basalts are very depleted i n the most incompatible elements). Results of trace element mixing models are shown in Figure 4 9. As expected, the Sr/Sr* value of the mix composition decreases as the proportion of the Lamont melt increases. The small increase in (La/Sm) N and (Ce/Yb) N in comparison to the increase in Sr/Sr* suggests that small degree gabbro melts (maximum F of 0.1) mixed with Lamont basalts. Calculated (La/Sm) N values indicate that most of the high Sr Lamont compositions can be explained by mixing of small degree gabbro m elts with depleted Lamont basalts in a ratio of 35:65. Calculated (Ce/Yb) N values suggest that a somewhat larger proportion (proportions up to 90% gabbro melts:10% depleted Lamont melt) of gabbroic melt is needed to explain the anomalous compositions, howe ver. In a few lavas, calculated Sr concentrations are not high enough to match the highest Sr concentrations in Lamont basalts. This, together with higher abundances of some other incompatible elements suggests that the models parameters may not be correct and, more likely, that there is a range of gabbroic compositions that could serve as assimilants. Several researchers have modeled the effect of assimilation of troctolite on typical MORB compositions [Kvassnes and Grove, 2008; Lissenberg and Dick, 2008; Dick et al., 2010]. Their geochemical models suggest that the hybrid melts become enriched in Al 2 O 3 and MgO and depleted in CaO and SiO 2 after assimilation of a troctolite composition. This is more consistent with the major element compositions of Lamont high Al, high Sr basalts than assimilation of a gabbroic composition and suggests that

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97 the actual composition of the assimilant in the high Al, high Sr lavas could be more similar to a troctolite. More geochemical modeling is needed to investigate the effe cts of assimilating variable rock types on the chemistry of Lamont basalts. Mantle S ource s, Heterogeneity and Melting Many researchers have argued that the mantle source for the Lamont seamount chain is heterogeneous [Fornari et al., 1988a ,b; Allan et a l., 1989; Lundstrom et al., 1999]. Subsequent studies of other off axis lavas near the EPR has revealed even more geochemical heterogeneity than that documented at the Lamont seamount chain and offers more support for the heterogeneous nature of the mantle underneath the EPR [Niu and Batiza, 1997; Niu et al., 2002]. W hen compared to lavas from near ridge seamount chains and individual seamounts located between ~15 N and 7 N along the EPR (detailed in Niu and Batiza [1997] and Niu et al. [2002]), Lamont sa mples represent some of most incompatible trace element depleted basalts in the region (Fig. 5). For example, minimum (La/Sm) N for Lamont basalts is 0.23 whereas other EPR off axis basalts have a minimum (La/Sm) N of 0.31. Lavas from the Lamont seamount cha in also consistently have less radiogenic 87 Sr/ 86 Sr and Pb isotopic ratios and higher 143 Nd/ 144 Nd ratios than other off axis sites near the EPR (Fig. 4 7). It is important to note that the Lamont seamount chain lacks any enriched basalts, which have been d ocumented and are common at some other EPR seamounts [Niu and Batiza, 1997; Niu et al., 2002]. EPR seamounts have a maximum (La/Sm) N of 3.74 [Niu and Batiza, 1997; Niu et al., 2002], while Lamont samples only range up to a maximum (La/Sm) N of 0.71. Some ot her EPR seamount chains even host both trace element depleted and enriched samples [Niu and Batiza, 1997; Niu et al., 2002], while Lamont seamounts

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98 appear to only be comprised of incompatible trace element depleted basalts. The very depleted nature of the basalts coupled with their isotopic compositions suggests that the mantle source(s) for Lamont lavas is more incompatible trace element depleted than other areas along the EPR or that prior melting in the ridge environment extracted the enriched mantle com ponents. Cousens et al. [1995] and Geshi et al. [2007] suggested that extremely depleted, off axis lavas could be explained by re melting of mantle that had already been partially melted at the ridge axis. If this is the case for the Lamont lavas, then se amount isotopic ratios should be the same as lavas erupted at the ridge axis. However, this is not the case. In fact, there is a clear correlation between degree of trace element enrichment and isotopic ratios (Fig. 4 8), suggesting that geochemical variat ion found at the Lamont seamount chain is caused by small degrees of ancient source variation, rather than changes in degree of melting alone The most detailed study to date on an individual seamount chain is on the Vance seamount chain located on the wes t side of the Juan de Fuca ridge (JdFR) at ~45 N (see Chapter 2), and thus is a useful dataset to compare to the Lamont seamount chain. The Vance seamount chain is composed of five seamounts and two less structured edifices composed of pillow mounds and r idges. Similar to the Lamont seamounts, the geochemistry of basalts from the Vance seamounts ranges from extremely depleted in incompatible elements to slightly enriched, and these lavas are more isotopically heterogeneous than lavas from the adjacent Vanc e ridge segment. The Vance and Lamont seamount chains have similar major element trends including a large range in MgO concentrations and some high Al 2 O 3 samples (Fig. 4 2).

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99 Vance basalts range to higher concentrations of K 2 O than the Lamont seamount chai n, consistent with the more enriched trace element signature of Vance lavas. As seen in Figure 4 5, the Lamont seamount chain hosts basalts that range to slightly more trace element depleted values and are less heterogeneous than the Vance seamounts (ex. V ance (La/Sm) N : 0.309 1.06; Lamont (La/Sm) N : 0.23 0.71). Similar to regional off axis seamounts along the EPR, the Vance seamount chain has slightly higher 87 Sr/ 86 Sr and Pb isotopic ratios and lower 143 Nd/ 144 Nd than the Lamont seamount chain (Fig. 4 7). As discussed in Chapter 2, the heterogeneous trace element and isotopic signatures of the Vance seamount chain were likely caused by melting and mixing of a heterogeneous mantle source (composed of trace element depleted and enriched end members). The fact that no trace element enriched basalts have been sampled thus far at the Lamont seamount chain suggests that its mantle source does not contain the enriched end member (or only contains very small amounts) inferred to exist for enriched samples from other seamounts along the EPR [Niu and Batiza, 1997; Niu et al., 2002]. To better constrain the petrogenesis of Lamont seamount basalts alphaMELTS was used to calculate the composition of aggregated MORB melts formed under typicael mid ocean ridge conditions (s ee Chapter 2). This was accomplished by integrating instantaneous melt compositions from a source with the composition of average depleted mantle (Fig. 10) (DMM of Workman and Hart [2005]) under temperatures and pressures that produce a model crustal thick ness of ~7 km (consistent with the thickness of the EPR ridge near the Lamont seamount chain; Toomey and Hooft [2008]). The model results indicate that while some of the less trace

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100 element depleted lavas can be modeled by melting at a minimum ~12%, the mos t depleted compositions cannot be modeled by melting mantle with the composition of DMM. This supports the idea that the source for the Lamont seamount chain could have been remelted. Summary Our results indicate that the Lamont seamount chain not only ho sts lavas that likely have an incompatible element depleted mantle signature, but the chain also includes lavas that have been modified by crustal assimilation processes. This means that near ridge seamounts can offer a better view of mantle source/melting processes but may also be affected by complex melt rock reactions occurring in the oceanic crust that are likely obscured by homogenization in the large magma chambers at the ridge axis. Our geochemical reanalysis of Lamont basalts has revealed that thes e ba salts are variably LREE element depleted and have a small range in isotopic compositions. Trace element and isotopic compositions of Lamont basalts unaffected by assimilation compared to basic mantle melting models indicate that the most LREE depleted basalts cannot be explained by melting of DMM mantle under typical mid ocean ridge conditions and that the mantle source for the Lamont seamount chain likely is in general more depleted and less heterogeneous than the sources for other seamounts formed alo ng the EPR.

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101 Figure 4 1. Map of the Lamont seamount chain. This near ridge seamount chain is located at ~9 10 N on the Pacific plate near the East Pacific Rise (EPR). The chain is composed of five seamounts (NEW, DTD, MOK, MIB, and Sasha) that range in height from 800 to 1400 m [Allan et al., 1988]

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102 Figure 4 2. Major element plots showing Lamont glasses [Allan et al., 1988] and EPR axis basalts (EPR data field from Marine Geoscience Data System compilation: http://www.marinegeo.org/tools/search/Files.php?data_set_uid=9409 ; references: Perfit and Chadwick, [1998], Sims et al. [2002], Goss et al. [2010], and Waters et al., [2011]) compared to another well stu died near ridge seamount chain, the Vance seamount chain (located at ~45 N Juan de Fuca Ridge (JdFR) [see Chapter 2]. Lamont seamount basalts range to higher MgO concentrations and lower K 2 O concentrations than ridge basalts. The Lamont and Vance seamount chain have similar major element trends. They both range to primitive MgO concentrations and some of their lavas have high Al 2 O 3 concentrations (could indicate crustal gabbro assimilation). Some Vance seamount basalts, however, have higher K 2 O concentratio ns, suggesting that Lamont samples either do not host more enriched lavas sometimes found at other near ridge seamount chains or that these lavas have not yet been sampled at the Lamont seamount chain

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103 Figure 4 3. Comparison of Lamont glass reanalysis for selected trace elements and isotopes using ICP MS at University of Florida in comparison to XRF/INAA/TIMS analyses published by Allan et al. [1988] and Fornari et al. [1988a]. Most XRF/INAA trace element concentrations from the original stud y of the Lamont seamounts are higher than the analyses by ICP MS, as seen in results for Y and Zr. Trace elements Sr, Yb, Sm, Ce, and La XRF/INAA trace element concentrations analyzed by XRF/INAA are consistent with ICP MS analysis, (e.g. Sm and Ce plots). Original XRF/INAA data for these elements were used in plots for samples that could not be reanalyzed. In general, new ICP MS data produced lower radiogenic Sr and Pb values and more radiogenic Nd values for Lamont lavas than the original TIMS data. The r eason for this change is that we leached the glasses to remove any seawater alteration or Fe Mn oxide contamination prior to analysis, whereas the original study did not. Arrows show the change in isotopic ratios in individual samples from analyses origina lly published to new ICP MS values

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104 Figure 4 4. Plots of MgO concentrations versus a set of trace elements (see Figure 4 2 caption for EPR data field references). General trace element trends for Lamont basalts include decreasing compatible element c oncentrations (e.g. Ni) with decreasing MgO concentrations and increasing incompatible element concentrations with decreasing MgO concentrations. In general, Lamont samples have a greater range in Ni and Sr concentrations and range to lower Rb, Zr, Y, La, Ce, Sm, and Yb concentrations in comparison to EPR basalts

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105 Figure 4 4. Continued

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106 Figure 4 5. Plots of trace elements versus trace element ratios comparing Lamont basalts and EPR basalts (see Figure 4 2 caption for EPR data field references), to other EPR seamounts [Niu and Batiza, 1997; Niu et al., 2002], and the Vance seamount chain [see Chapter 2.]. Lamont samples range to lower (La/Sm) N (Ce/Yb) N Zr/Y, and Sr values in comparison to EPR lavas. Lamont lavas plot in the more incompatible trace element depleted portions of the EPR seamount and Vance fields, but lack more enriched basalts commonly found at EPR seamounts and only rarely found in the Vance seamount chain. High Al, high Sr basalts likely formed due to gabbro assimilation in the crust range to the some of the highest Sr, Zr/Y, (La/Sm) N and (Ce/Yb) N values found at the Lamont seamount chain

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107 Figure 4 6. Chondrite normalized REE and mantle normalized diagrams of Lamont basalts in comparison to EPR N MORB (see Figure 4 2 caption for EPR data field references). Lamont lavas are generally more depleted in the most incompatible LREEs and LILs. Some samples are slightly depleted in the HREEs in comparison to the MREEs, but some lavas from the EPR also have this signature. The samples mar ked with dashed lines from DTD, MOK, MIB, and Sasha are high Al, high Sr samples and have noticeable positive Sr anomalies. They also have elevated La and Ce normalized values, creating a humped pattern in many of the samples. These lavas also range to the most depleted LILE values found at the Lamont seamount chain. The trace element signature of these samples is likely caused by assimilation of crustal gabbro

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108 Figure 4 6. Continued

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109 Figure 4 7. Plots of Sr Nd Pb isotopic ratios in comparison to EPR basalts (see Figure 4 2 caption for EPR data field references), other EPR seamounts [Niu and Batiza, 1997; Niu et al., 2002], and the Vance seamount chain [see Chapter 2.]. Pb isotopic trends are fairly linear, but there is more scatter for the 87 Sr/ 86 Sr 1 43 Nd/ 144 Nd trend. Except for two samples, Lamont basalts have less radiogenic Sr and Pb values and more radiogenic Nd values than EPR axis and seamount basalts and Vance seamount basalts. This suggests that the Lamont lavas are tapping a mantle source that than the other sites. High Al, high Sr basalts have slightly lower 87 Sr/ 86 Sr values, but no trends exist for the other isotopes, indicating that isotopic composition of gabbros assimilated by these lavas was very similar

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110 Figure 4 8. Trace element ratios versus 143 Nd/ 144 Nd (see Figure 4 2 caption for EPR data field references). Both (La/Sm) N and (Ce/Yb) N increase as 143 Nd/ 144 Nd decreases. The two samples with the lowest radiogenic Nd also follow this trend, suggesting that they do represent mantle isotopic values and are not necessarily affected by seawater contamination. The clear correlation between isotopic and trace element ratios suggests that the geochemical variation in Lamont lavas is caused by small degree sour ce variations, rather than melting variation alone

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111 Figure 4 9. Major and trace element assimilation models for gabbro composition and N MORB and Lamont melts. Major element assimilation models were calculated using alphaMELTS [Ghiorso and Sack, 1995; Asimow and Ghiorso, 1998; Smith and Asimow, 2005; Antoshechkina et al., 2010]. Assimilating a gabbro into a typical primitive MORB composition resulted in high MgO basalts that, after undergoing fractional crystallization (modeled using Petrolog [Dan yushevsky and Plechov, 2011]), were too low in Al 2 O 3 concentrations. Assimilation of more evolved Lamont basalt compositions resulted in similar Al 2 O 3 concentrations to the high Al, high Sr basalts. Trace element assimilation models were calculated assumin g that batch partial melts of gabbro mixed with a depleted Lamont basalt. Most high Al, high Sr lavas can be explained by mixing a depleted melt composition with small degree partial melts of gabbro (max. F=0.1). As seen in the primitive mantle normalized diagram, these hybrid lavas have similar positive Sr anomalies as well as similar depleted LIL compositions to the high Al, high Sr lavas. Some elevated trace element concentrations cannot be explained by the assimilation model, however, suggesting that ga bbros of varying trace element compositions could have been assimilated by Lamont lavas

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112 Figure 4 10. Trace element melting model from Chapter 2 in comparison to the trace element compositions of the Lamont seamount chain (see Figure 4 2 caption for E PR data field references). Some of the less depleted basalts from the Lamont seamount chain can be explained by a minimum of 12% melting of DMM mantle, but the most depleted Lamont compositions cannot be modeled by melting DMM mantle. This suggests that ei ther the composition of the mantle underneath the Lamont chain is more depleted than DMM or that the mantle source for the Lamont lavas was re melted

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113 CHAPTER 5 CONCLUSION Off axis volcanism along the JdFR and the EPR is geochemically heterogeneous and likely represents sampling of varying proportions of two component mantle, which is masked by magma chamber homogenization at the ridge. Rogue seamount is the most LREE depleted seamount analyzed in this study and best represents the more depleted mant le component. Melting of typical DMM [Workman and Hart, 2005] cannot produce melts depleted enough to explain the chemistry of Rogue basalts or more depleted basalts from Vance and Lamont seamount chain, suggesting that either the mantle source for these l avas was previously partially melted or that it is more long term depleted than the source for ridge mantle. Isotopic trends indicate that JdFR lavas can be explained by mixing between DMM and HIMU mantle components. Lamont seamount lavas could also be for med by mixing of heterogeneous mantle but the isotopic signature for the more enriched component is less clear. Some Lamont basalts do record assimilation of gabbroic material at crustal levels. These lavas have high Al 2 O 3 and Sr concentrations in comparis on to lavas unaffected by assimilation. The fact that chemical signatures of both mantle and crustal processes can be found in seamount basalts indicates that the study of off axis volcanism can help us better understand melting processes that are obscured by homogenization at the ridge axis.

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114 APPENDIX A REPRODUCIBILITY AND ACCURACY OF ICP MS TRACE ELEMENT ANA LYSIS FOR AGV 1 AND 2392 1

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115 Table A 1. Reproducibility and accuracy for trace element data for AGV 1 Analysis #/Element #1 #2 #3 #4 #5 #6 #7 # 8 Mean Std. dev. St. dev. Ref. Value 1 Rel. dev. (%) Sc (ppm) 11.7 12.4 12.2 12.1 11.8 11.9 12.0 11.4 11.9 0.3 2.7 12.2 2.3 V (ppm) 121 114 121 120 117 123 117 118 119 3 2.4 121.0 1.7 Cr (ppm) 10.8 11.9 10.9 10.6 9.8 10.8 10.2 1 0.8 10.7 0.6 5.7 10.1 6.3 Co (ppm) 15.1 14.5 15.1 15.1 15.0 14.8 14.9 14.9 14.9 0.2 1.4 15.3 2.5 Ni (ppm) 15.8 18.5 14.7 18.2 14.8 16.6 15.1 15.9 16.2 1.5 9.0 16.0 1.3 Cu (ppm) 58.0 57.2 60.3 58.5 59.0 61.7 60.3 57.0 59.0 1.7 2.8 60.0 1.7 Zn (ppm) 88 .9 87.5 89.9 89.6 88.9 90.9 89.8 87.5 89.1 1.2 1.3 88.0 1.3 Ga (ppm) 20.3 20.7 21.1 20.4 19.8 21.3 21.0 20.5 20.6 0.5 2.4 20.0 3.1 Rb (ppm) 67.6 67.3 67.6 66.4 66.3 65.7 67.0 68.3 67.0 0.8 1.2 67.3 0.4 Sr (ppm) 642 662 676 656 660 656 656 669 660 10 1 .5 662.0 0.3 Y (ppm) 19.4 19.7 20.1 20.4 19.0 21.9 19.8 19.9 20.0 0.9 4.5 20.0 0.1 Zr (ppm) 215 229 229 232 225 226 228 229 227 5 2.2 227.0 0.1 Nb (ppm) 14.2 15.2 14.8 14.5 14.7 14.8 14.8 14.8 14.7 0.3 2.0 15.0 1.8 Ba (ppm) 1227 1156 1216 1203 1263 12 19 1313 1201 1225 47 3.8 1226.0 0.1 La (ppm) 39.6 38.3 38.7 38.8 38.3 38.0 39.3 37.8 38.6 0.6 1.7 38.0 1.5 Ce (ppm) 68.7 69.4 70.2 71.1 69.2 70.6 71.4 68.8 69.9 1.0 1.5 67.0 4.4 Pr (ppm) 8.3 8.2 8.4 8.5 8.2 8.3 8.4 8.1 8.3 0.1 1.6 7.6 9.0 Nd (ppm) 3 1.3 30.4 30.8 31.4 29.9 30.5 33.5 29.9 31.0 1.2 3.7 33.0 6.1 Sm (ppm) 5.9 5.8 5.9 5.9 5.8 5.8 6.0 5.8 5.9 0.1 1.2 5.9 0.8 Eu (ppm) 1.72 1.66 1.68 1.71 1.62 1.70 1.74 1.65 1.68 0.04 2.5 1.6 2.7 Gd (ppm) 4.8 5.0 5.1 5.1 4.8 5.2 5.2 4.9 5.0 0.2 3.1 5.0 0. 0 Tb (ppm) 0.70 0.67 0.70 0.70 0.66 0.73 0.71 0.69 0.69 0.02 3.2 0.7 1.1 1 http://crustal.usgs.gov/geochemical_reference_standards/andesite1.htm l

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116 Table A 1. Continu ed Analysis #/Element #1 #2 #3 #4 #5 #6 #7 #8 Mean Std. dev. St. dev. Ref. Value 1 Rel. dev. (%) Dy (ppm) 3.6 3.5 3.7 3.7 3.5 3.7 3.7 3.6 3.6 0.1 2.4 3.6 0.4 Ho (ppm) 0.69 0.66 0.69 0.70 0.66 0.72 0.69 0.68 0.68 0.02 2.9 0.7 2.2 Er (ppm) 1.86 1.86 1.92 1.89 1.85 1.95 1.93 1.90 1.90 0.04 1.9 1.7 11.5 Tm (ppm) 0.27 0.26 0.27 0.26 0.26 0.28 0.27 0.26 0.27 0.01 3.1 0.3 21.6 Yb (ppm) 1.66 1.65 1.68 1.71 1.63 1.77 1.69 1.66 1.68 0.04 2.6 1.7 2.2 Lu (ppm) 0.26 0.25 0.26 0.2 6 0.24 0.27 0.26 0.24 0.25 0.01 3.2 0.3 6.2 Hf (ppm) 5.3 5.1 5.2 5.3 5.0 5.2 5.3 5.1 5.2 0.1 2.4 5.1 1.5 Ta (ppm) 0.89 1.03 0.88 0.89 0.90 0.88 0.88 0.86 0.90 0.05 6.0 0.9 0.3 Pb (ppm) 33.3 37.4 39.0 38.1 37.2 38.2 38.4 37.7 37.4 1.8 4.7 36.0 4.0 Th (ppm) 6.6 6.3 6.4 6.4 6.5 6.4 6.4 6.3 6.4 0.1 1.7 6.5 1.3 U (ppm) 2.03 1.92 1.94 1.94 1.90 1.92 1.96 1.92 1.94 0.04 2.1 1.9 1.1 1 http://crustal.usgs.gov/geochemical _reference_standards/andesite1.htm l

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117 Table A 2. Reproducibility and accuracy for trace element data for 2392 Analysis #/Element #1 #2 #3 #4 #5 #6 #7 #8 #9 Mean Std. dev. St. dev. Ref. Value Rel. dev. (%) Sc (ppm) 36.6 37.7 37.1 37.6 38.9 34.3 39.0 38.6 36.5 37.4 1.5 4.0 37.4 0.1 V (ppm) 262 258 260 255 276 238 263 263 269 261 11 4.0 256 1.8 Cr (ppm) 344 334 338 325 318 312 327 328 334 329 10 3.0 300 9.7 Co (ppm) 42.3 42.8 42.4 40.6 41.0 38.6 41.7 42.3 42.0 41.5 1.3 3.2 39 6.4 Ni (ppm) 114 112 112 109 118 107 111 112 111 112 3 2.9 113 1.1 Cu (ppm) 75 73 74 72 77 68 73 71 71 73 3 3.6 76 4.6 Zn (ppm) 74.7 72.5 72.1 70.8 75.2 70.8 73.5 71.7 71.0 72.5 1.7 2.3 78.4 7.6 Ga (ppm) 16.8 16.2 16.8 15.6 16.9 15.1 16.4 16.1 16.7 16.3 0.6 3.8 16 1.8 Rb (ppm) 0.62 0.84 0.82 0.89 0.84 0.86 0.95 0.80 0.82 0.83 0.09 10.7 0.91 9.2 Sr (ppm) 118 120 127 119 118 113 119 121 121 119 4 3.2 11 6 3.0 Y (ppm) 27.0 28.9 28.5 28.4 29.7 25.5 29.9 28.3 27.7 28.2 1.4 4.8 30.15 6.5 Zr (ppm) 79 79 78 97 83 71 81 77 76 80 7 9.0 85 5.7 Nb (ppm) 2.36 2.38 2.34 2.35 2.32 2.11 2.28 2.36 2.42 2.32 0.09 3.9 2.2 5.6 Ba (ppm) 8.0 8.3 8.5 8.5 6.7 7.8 7.0 8.2 9.2 8.0 0.8 9.6 8 0.3 La (ppm) 2.9 3.0 2.7 3.0 3.1 2.8 2.8 2.9 2.8 2.9 0.1 4.2 3 3.6 Ce (ppm) 9.3 9.2 8.8 9.2 9.8 8.7 9.1 9.0 8.8 9.1 0.3 3.5 9.58 4.8 Pr (ppm) 1.60 1.58 1.53 1.57 1.65 1.48 1.57 1.55 1.51 1.56 0.05 3.2 1.64 4.9 Nd (ppm) 8.6 8.3 8.3 8 .4 9.0 7.8 8.5 8.3 8.4 8.4 0.3 3.8 8.86 5.1 Sm (ppm) 3.0 2.9 2.9 2.8 3.0 2.7 2.9 3.0 2.9 2.9 0.1 3.8 2.9 0.4 Eu (ppm) 1.08 1.05 1.07 1.04 1.12 0.97 1.07 1.06 1.04 1.06 0.04 3.7 1.1 3.9 Gd (ppm) 3.9 3.8 3.9 3.8 4.1 3.6 3.9 3.8 3.8 3.8 0.1 3.2 4.08 5.9 Tb (ppm) 0.72 0.71 0.70 0.72 0.74 0.66 0.71 0.72 0.72 0.71 0.02 3.3 0.74 3.9

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1 18 Table A 2. Continued Analysis #/Element #1 #2 #3 #4 #5 #6 #7 #8 #9 Mean Std. dev. abs) St. dev. %) Ref. Value Rel. dev. (%) Dy (ppm) 4.6 4.6 4.6 4.6 4.9 4.2 4.6 4.7 4.6 4.6 0.2 3.6 4.7 1.9 Ho (ppm) 0.98 1.00 0.97 0.97 1.02 0.91 0.99 1.00 1.00 0.98 0.03 3.3 1.03 4.8 Er (ppm) 2.8 2.8 2.8 2.8 2.9 2.6 2 .8 2.9 2.9 2.8 0.1 3.7 2.89 2.4 Tm (ppm) 0.42 0.43 0.42 0.42 0.44 0.39 0.43 0.44 0.44 0.43 0.01 3.1 0.45 5.4 Yb (ppm) 2.67 2.75 2.78 2.77 2.81 2.54 2.71 2.79 2.80 2.74 0.09 3.1 2.84 3.7 Lu (ppm) 0.40 0.42 0.41 0.42 0.44 0.39 0.42 0.41 0.41 0.41 0.01 3.2 0.45 8.3 Hf (ppm) 2.1 2.1 2.1 2.5 2.2 2.0 2.1 2.2 2.1 2.2 0.1 6.8 2.18 0.9 Ta (ppm) 0.156 0.145 0.155 0.152 0.158 0.143 0.150 0.152 0.154 0.152 0.005 3.4 0.16 5.2 Pb (ppm) 0.36 0.44 0.39 0.38 0.27 0.28 0.40 0.26 0.46 0.36 0.08 21.1 0.2 80.5 Th (ppm) 0.15 0.17 0.16 0.14 0.14 0.14 0.17 0.17 0.15 0.01 9.2 0.12 28.1 U (ppm) 0.070 0.072 0.070 0.067 0.055 0.057 0.063 0.060 0.071 0.065 0.006 10.0 0.05 30.2

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119 APPENDIX B TRACE ELEMENT AND IS OTOPIC RATIOS OF VAN CE SEAMOUNT BASALTS

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120 Table B 1. Major and t race element concentrations and isotopic ratios from basalts from the Vance seamount chain and the Vance ridge segment Sample T1008 R05A 1,3,4 T1008 R05B 1,3 T1008 R08 1,3 T1008 R20 1,3,4 T1008 R22 1,3 T1008 R23 1,3,4 T1012 PC11 1 T1012 R01 1,3,,4 T1012 R 02 1 T1012 R04 1 Seamount A A A A A A B B B B Longitude 130.843 130.843 130.842 130.832 130.836 130.837 130.688 130.688 130.690 Latitude 45.658 45.658 45.660 45.674 45.676 45.677 45.641 45.641 45.640 Depth (m) 1916.9 1916.9 1791.6 1705.9 1776.0 1792. 4 2162.7 2162.4 2151.1 Major elements (wt. %) SiO 2 49.20 49.23 49.20 49.65 49.57 49.59 47.80 47.95 48.41 47.83 TiO 2 1.32 1.25 1.60 1.71 1.20 1.16 1.07 1.41 1.18 1.36 Al 2 O 3 16.57 16.55 16.88 15.43 16.22 16.30 17.72 16.82 17.65 16.91 FeO T 9.05 9.04 9.50 9.93 8.87 9.24 9.32 10.94 10.73 10.90 MnO 0.16 0.15 0.16 0.18 0.16 0.17 0.14 0.18 0.18 0.19 MgO 8.35 8.32 7.93 7.25 8.39 8.57 8.49 7.89 8.24 7.93 CaO 12.20 12.25 11.78 12.07 12.45 12.44 11.66 11.63 11.53 11.65 Na 2 O 2.46 2.45 2.98 2.85 2.49 2 .47 2.84 2.76 2.48 2.71 K 2 O 0.23 0.24 0.23 0.31 0.10 0.09 0.05 0.06 0.05 0.07 P 2 O 5 0.13 0.14 0.17 0.18 0.09 0.08 0.07 0.08 0.06 0.08 S 0.10 0.10 0.10 0.11 0.09 0.09 0.10 0.11 0.11 0.11 Cl 0.03 0.03 0.02 0.01 0.02 0.01 0.00 0.00 0.00 0.00 Total 99.82 9 9.78 100.54 99.67 99.65 100.22 99.26 99.83 100.62 99.75 Trace elements (ppm) Sc 35.1 34.8 35.6 47.1 44.6 32.2 45.5 36.3 V 237 232 244 261 233 198 308 196 Cr 287 286 248 305 335 291 191 292 Co 40.1 41.3 39.7 38.2 40.6 36.2 44.1 50.8 N i 122.1 123.7 123.5 79.7 88.1 84.0 54.9 209.9 Cu 75.6 74.7 67.0 72.8 81.7 77.5 84.8 85.9 Zn 70.2 69.3 73.3 73.3 69.4 62.5 80.0 75.2 Ga 16.7 16.6 18.1 17.7 16.2 14.2 16.8 16.2 Rb 1.67 1.67 1.38 2.07 0.77 0.63 0.76 0.42 Sr 171 167 193 202 117 103 88 115 Y 25.8 25.3 29.9 29.0 25.1 22.1 32.2 25.5 Zr 87.0 88.3 110.1 111.7 59.2 52.1 76.0 62.3 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

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121 Table B 1. Continued Sample T1008 R05A 1,3,4 T1008 R05B 1,3 T1008 R08 1,3 T1008 R20 1,3,4 T1008 R22 1,3 T1008 R23 1,3,4 T1012 PC11 1 T1012 R01 1,3,,4 T1012 R02 1 T1012 R04 1 Trace elements (ppm) N b 4.70 4.90 4.90 6.23 1.99 1.80 1.81 1.20 Ba 19.51 20.09 16.67 24.88 9.62 7.93 9.36 6.62 La 4.47 4.56 4.80 5.85 2.32 2.02 2.55 1.94 Ce 12.01 12.43 13.94 15.56 6.93 6.25 8.06 6.64 Pr 1.82 1.88 2.22 2.37 1.20 1.06 1.43 1.16 Nd 9.27 9.27 11.15 11.69 6.66 6.04 8.10 6.45 Sm 2.91 2.92 3.57 3.55 2.44 2.17 2.88 2.37 Eu 1.10 1.09 1.30 1.29 0.96 0.87 1.11 0.96 Gd 3.73 3.79 4.40 4.40 3.45 3.05 4.12 3.25 Tb 0.66 0.68 0.77 0.77 0.64 0.56 0.79 0.63 Dy 4.22 4.31 4.86 4.82 4.10 3.60 5.15 4.13 Ho 0.87 0.90 1.04 1.00 0.88 0.77 1.13 0.89 Er 2.51 2.61 2.86 2.80 2.51 2.17 3.26 2.59 Tm 0.38 0.38 0.44 0.42 0.39 0.34 0.49 0.40 Yb 2.45 2.44 2.75 2.71 2.43 2.13 3.19 2.62 Lu 0.36 0.38 0.43 0.41 0.37 0.32 0.48 0.40 Hf 2.20 2.22 2.69 2.79 1.75 1.55 2.17 1.70 Ta 0.320 0.320 0.320 0.410 0.130 0.120 0.120 0.080 Pb 0.303 0.328 0.396 0.498 0.112 0.060 0.052 0.099 Th 0.275 0.279 0.273 0.352 0.104 0.100 0.103 0.109 U 0.121 0.120 0.118 0.152 0.053 0.046 0.044 0.044 208 Pb/ 204 Pb 37.920 38.106 38.214 38.324 5.00E 03 7.00E 03 5.00E 03 1.67E 03 207 Pb/ 204 Pb 15.492 15.543 15.538 15.500 2.00E 03 2.00E 03 2.00E 03 6.54E 04 206 Pb/ 204 Pb 18.500 18.526 18.580 18.807 2.00E 03 2.00E 03 3.00E 03 7.07E 04 143 Nd/ 144 Nd 0.51311 0.51311 0.51313 0.51311 1.20E 05 8.00E 06 9.00E 06 4.80E 06 87 Sr/ 86 Sr 0.70262 0.70276 0.70276 0.70249 6.00E 06 1.10E 05 1.20E 05 1.20E 05 1 Major elements from Wendt [2008] 2 Majo r elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 122

122 Table B 1. Continued Sample T1012 R05 1 T1012 R06 1 T1012 R07 1 T1012 R08 1,3,4 T1012 R09 1,3 T1012 R1 0 1 T1012 R11 1 T1012 R12 1 T1012 R13 1 1012 R14A 1,3,4 Seamount B B B B B B B B B B Longitude 130.682 130.679 130.677 130.676 130.673 130.671 130.670 130.668 130.667 130.666 Latitude 45.639 45.638 45.638 45.637 45.637 45.638 45.638 45.638 45.637 45.637 Depth (m) 2128.2 2209.2 2273.0 2257.6 2162.5 2082.6 2088.7 2047.2 2037.0 1976.0 Major elements (wt. %) SiO 2 48.34 48.29 48.12 47.78 47.96 47.92 47.93 48.13 47.78 47.92 TiO 2 1.11 1.17 1.28 1.23 1.16 1.18 1.19 1.25 1.13 1.18 Al 2 O 3 17.49 17.38 17.75 17.17 17.82 17.86 17.80 17.44 17.72 17.77 FeO T 10.71 10.90 9.81 10.10 9.54 9.48 9.49 9.97 9.82 9.64 MnO 0.18 0.18 0.17 0.19 0.16 0.16 0.17 0.16 0.16 0.16 MgO 8.70 8.38 8.30 9.13 8.51 8.51 8.50 8.09 8.80 8.64 CaO 11.36 11.39 11.72 11.37 11.62 11.5 8 11.60 11.65 11.51 11.42 Na 2 O 2.45 2.50 2.85 2.68 2.83 2.85 2.82 2.92 2.71 2.81 K 2 O 0.04 0.06 0.05 0.06 0.05 0.05 0.04 0.05 0.04 0.04 P 2 O 5 0.05 0.06 0.07 0.08 0.06 0.05 0.07 0.09 0.05 0.07 S 0.11 0.11 0.11 0.10 0.09 0.10 0.10 0.11 0.10 0.10 Cl 0.00 0 .00 0.00 0.01 0.00 0.00 0.00 0.00 0.00 0.00 Total 100.55 100.42 100.22 99.89 99.79 99.75 99.71 99.87 99.83 99.74 Trace elements (ppm) Sc 35.1 38.9 31.9 35.3 41.4 36.1 36.6 37.4 V 192 202 183 198 190 195 192 216 Cr 308 304 219 450 238 279 319 265 Co 48.8 49.8 43.0 54.1 43.3 46.2 49.3 46.8 Ni 194.7 180.2 148.1 314.3 145.8 153.9 205.6 168.0 Cu 86.5 85.4 78.4 82.8 73.8 75.6 86.0 80.7 Zn 69.7 70.4 63.1 75.7 66.3 67.1 65.1 72.9 Ga 15.1 16.1 15.3 15.6 16.3 16.4 15.2 16.8 Rb 0.37 0.50 0.35 0.57 0.43 0.48 0.32 0.59 Sr 112 123 152 137 156 166 151 149 Y 23.3 25.8 22.1 26.6 26.2 26.0 26.0 27.3 Zr 55.0 58.7 68.1 74.9 74.2 71.1 69.1 78.1 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace ele ments from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 123

123 Table B 1. Continued Sample T1012 R05 1 T1012 R06 1 T1012 R07 1 T1012 R08 1,3,4 T1012 R09 1,3 T1012 R10 1 T1012 R11 1 T1012 R12 1 T1012 R13 1 1012 R14A 1,3,4 Trace elements (ppm) Nb 1.12 1.20 1.09 1.70 1.06 1.11 1.12 1.51 Ba 6.32 6.76 5.77 7.66 5.52 5.96 4.82 5.99 La 1.72 1.88 1.97 2.61 2.19 2.18 2.25 2.69 Ce 5.86 6.18 7.01 8.77 7.54 7.54 7.49 8.59 Pr 1.07 1.12 1.27 1.50 1.37 1 .37 1.34 1.49 Nd 6.08 6.33 7.11 7.99 7.56 7.69 7.30 8.09 Sm 2.28 2.39 2.55 2.73 2.60 2.69 2.54 2.71 Eu 0.92 0.95 0.99 1.07 1.03 1.07 1.03 1.07 Gd 3.25 3.33 3.38 3.63 3.51 3.60 3.47 3.64 Tb 0.63 0.64 0.62 0.67 0.64 0.67 0.65 0.68 Dy 4.08 4 .21 4.02 4.40 4.18 4.28 4.26 4.41 Ho 0.88 0.91 0.84 0.93 0.90 0.92 0.91 0.96 Er 2.60 2.66 2.46 2.75 2.56 2.65 2.62 2.76 Tm 0.39 0.40 0.37 0.41 0.39 0.40 0.41 0.40 Yb 2.53 2.63 2.35 2.75 2.53 2.58 2.64 2.64 Lu 0.39 0.40 0.35 0.43 0.39 0.39 0.40 0.41 Hf 1.72 1.80 1.94 1.94 1.95 1.99 1.86 2.06 Ta 0.082 0.086 0.083 0.110 0.070 0.081 0.086 0.110 Pb 0.135 0.286 0.288 0.238 0.245 0.326 0.426 0.126 Th 0.067 0.097 0.059 0.095 0.071 0.096 0.088 0.095 U 0.034 0.035 0.028 0.042 0.027 0.027 0.026 0.042 208 Pb/ 204 Pb 38.042 37.960 37.850 38.077 37.889 38.138 6.03E 03 4.97E 03 1.30E 02 6.00E 03 3.58E 03 9.00E 03 207 Pb/ 204 Pb 15.525 15.505 15.459 15.511 15.482 15.527 1.88E 03 1.95E 03 4.04E 03 2.00E 03 1.44E 03 3.00E 03 206 Pb/ 204 Pb 18.650 18.610 18.563 18.699 18.560 18.631 1.77E 03 2. 21E 03 3.56E 03 2.00E 03 1.81E 03 3.00E 03 143 Nd/ 144 Nd 0.51317 0.51313 0.51306 0.51305 0.51307 6.40E 06 6.20E 06 9.70E 06 9.00E 06 5.90E 06 87 Sr/ 86 Sr 0.70251 0.70255 0.70253 0.70257 0.70251 0.70260 2.10E 05 2.60E 05 3.20E 05 9.0 0E 06 1.10E 05 1.20E 04 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 124

124 Table B 1. Continued Sample T 1012 R14B 1 T1012 R17 1 T1012 R18 1 T1012 R20 1 T1012 R21 1,3,4 T1012 R22 1 T1012 R23 1 T1013 GS7 1 T1013 R02 1,3,4 T1013 R14 1 Seamount B B B B B B B C C C Longitude 130.666 130.664 130.664 130.663 130.660 130.659 130.657 130.507 130.510 Latitude 45.6 37 45.634 45.633 45.632 45.629 45.629 45.627 45.450 45.451 Depth (m) 1976.0 1961.5 1975.4 1965.0 1988.0 1969.1 1974.2 2060.3 1924.0 Major elements (wt. %) SiO 2 47.89 48.10 48.02 48.12 50.63 48.16 48.14 49.81 49.93 50.52 TiO 2 1.10 1.19 1.28 1 .31 1.37 1.21 1.20 1.46 0.94 1.39 Al 2 O 3 17.76 17.76 17.59 17.40 14.55 17.84 17.79 14.98 15.74 14.56 FeO T 9.97 9.50 9.89 9.94 10.82 9.92 9.77 9.95 9.41 10.77 MnO 0.17 0.16 0.17 0.17 0.19 0.18 0.16 0.18 0.16 0.18 MgO 8.99 8.44 8.22 8.05 7.30 8.33 8.55 7. 52 8.60 7.34 CaO 11.48 11.63 11.59 11.67 12.11 11.46 11.49 12.15 12.82 12.05 Na 2 O 2.66 2.84 2.97 2.90 2.47 2.88 2.88 2.66 2.07 2.45 K 2 O 0.04 0.05 0.05 0.05 0.10 0.05 0.05 0.12 0.04 0.09 P 2 O 5 0.07 0.07 0.08 0.09 0.09 0.08 0.06 0.11 0.06 0.11 S 0.10 0.1 0 0.10 0.10 0.13 0.10 0.10 0.11 0.11 0.14 Cl 0.00 0.00 0.00 0.00 0.02 0.00 0.00 0.01 0.01 0.02 Total 100.24 99.83 99.96 99.79 99.78 100.22 100.18 99.07 99.90 99.63 Trace elements (ppm) Sc 36.3 32.1 37.2 46.5 V 195 189 198 253 Cr 235 218 345 372 Co 44.9 43.0 50.9 41.7 Ni 141.5 137.1 221.0 86.0 Cu 73.5 74.0 87.5 88.7 Zn 66.7 63.4 71.8 70.4 Ga 16.2 15.0 16.0 15.7 Rb 0.49 0.38 0.44 0.43 Sr 163 150 153 64 Y 26.1 24.7 26.6 24. 2 Zr 72.0 69.6 72.0 42.7 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 125

125 Table B 1. Continued Sampl e T1012 R14B 1 T1012 R17 1 T1012 R18 1 T1012 R20 1 T1012 R21 1,3,4 T1012 R22 1 T1012 R23 1 T1013 GS7 1 T1013 R02 1,3,4 T1013 R14 1 Trace elements (ppm) Nb 1.17 1.13 1.05 0.82 Ba 6.23 6.06 5.71 4.20 La 2.22 2.09 2.26 1.34 Ce 7.64 7.30 7.61 4.50 Pr 1.39 1.32 1.38 0.85 Nd 7.70 7.37 7.66 5.05 Sm 2.76 2.61 2.52 1.99 Eu 1.08 1.04 1.03 0.80 Gd 3.63 3.48 3.48 3.04 Tb 0.68 0.65 0.64 0.59 Dy 4.34 4.14 4.20 3.88 Ho 0.92 0.87 0.92 0.84 Er 2.64 2.54 2.66 2.45 Tm 0.40 0.38 0.40 0.37 Yb 2.59 2.44 2.62 2.44 Lu 0.39 0.37 0.39 0.37 Hf 1.99 1.98 1.90 1.38 Ta 0.085 0.083 0.080 0.050 Pb 0.317 0.367 0.153 0.005 Th 0.099 0.096 0.064 0.048 U 0.029 0.029 0.030 0.022 208 Pb/ 204 Pb 38.119 37.723 8.00E 03 3.98E 03 207 Pb/ 204 Pb 15.540 15.458 3.00E 03 1.80E 03 206 Pb/ 204 Pb 18.636 18.386 3.00E 03 2.18E 03 143 Nd/ 144 Nd 0.51307 0.51316 1.20E 05 1.10E 05 87 Sr/ 86 Sr 0.70263 0.70 261 1.30E 04 8.00E 06 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 126

126 Table B 1. Continu ed Sample T1013 R17 1,3,4 T1013 R18 1,4 T1013 R19 1 T1013 R20 1 T1013 R21 1,3,4 T1013 R22 1 T1013 R23 1 T1013 R24 1 T1013 R25 1 T1013 R27 1 Seamount C C C C C C C C C C Longitude 130.517 130.518 130.519 130.519 130.519 130.522 130.522 130.524 130.524 130 .525 Latitude 45.449 45.450 45.452 45.453 45.454 45.457 45.457 45.458 45.458 45.459 Depth (m) 1830.2 1906.7 1897.7 1887.9 1893.2 1866.2 1866.1 1857.8 1856.9 1824.3 Major elements (wt. %) SiO 2 48.79 50.60 50.31 50.26 50.21 50.37 50.35 50.30 50. 22 50.06 TiO 2 0.87 1.36 0.95 0.87 0.89 0.94 0.91 0.92 0.97 1.04 Al 2 O 3 17.26 14.47 15.52 15.64 15.57 15.54 15.54 15.49 15.53 15.39 FeO T 8.68 10.73 8.71 8.70 8.78 8.79 8.74 8.80 8.83 9.54 MnO 0.15 0.19 0.16 0.15 0.17 0.16 0.16 0.17 0.15 0.19 MgO 9.45 7. 34 8.44 8.51 8.54 8.48 8.49 8.49 8.47 8.31 CaO 12.52 12.16 13.23 13.26 13.14 13.31 13.19 13.24 13.25 12.85 Na 2 O 2.12 2.50 2.20 2.19 2.18 2.19 2.18 2.21 2.15 2.15 K 2 O 0.03 0.10 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.05 P 2 O 5 0.04 0.09 0.05 0.05 0.06 0.06 0 .06 0.05 0.07 0.07 S 0.09 0.13 0.09 0.09 0.10 0.10 0.10 0.10 0.09 0.11 Cl 0.00 0.02 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.01 Total 100.02 99.68 99.70 99.75 99.68 99.97 99.76 99.81 99.76 99.77 Trace elements (ppm) Sc 33.5 44.2 39.6 48.6 42.2 4 1.3 41.7 V 210 305 230 230 242 237 230 Cr 307 186 423 412 437 432 426 Co 45.2 41.9 42.3 40.5 44.4 42.3 41.4 Ni 151.2 45.4 90.6 88.0 91.9 86.7 90.0 Cu 87.1 71.4 90.5 89.1 96.1 93.3 92.5 Zn 65.1 85.2 60.1 63.7 65.4 62.3 64.5 Ga 15. 0 16.9 14.6 15.3 15.7 14.9 15.3 Rb 0.27 0.87 0.28 0.42 0.43 0.30 0.45 Sr 84 102 83 85 90 84 88 Y 21.7 32.0 19.1 21.7 21.2 16.7 21.8 Zr 48.4 68.9 40.6 42.4 39.2 41.2 38.0 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 127

127 Table B 1. Continued Sample T1013 R17 1,3,4 T1013 R18 1,4 T1013 R19 1 T1013 R20 1 T1013 R21 1,3,4 T1013 R22 1 T1013 R23 1 T1013 R24 1 T1013 R25 1 T1013 R27 1 Trace elements (ppm) Nb 0.80 2.14 0.87 0.88 0.95 0.90 0.92 Ba 3.56 11.23 4.43 5.39 6.12 4.53 5.97 La 1.39 2.87 1.39 1.43 1.34 1.37 1.34 Ce 5.16 8.61 4.38 4.73 4.43 4.32 4.39 Pr 0.95 1.50 0.83 0.88 0.84 0.82 0.84 Nd 5.47 8.21 4.74 5.09 4.98 4.73 4.97 Sm 1.97 2.99 1.84 1.91 2.01 1.84 2.01 Eu 0.81 1.12 0.76 0.79 0.80 0.73 0.79 Gd 2.88 4.07 2.62 2.80 2.88 2.65 2.85 Tb 0.55 0.79 0.51 0.52 0.55 0.50 0.54 Dy 3.58 5.13 3.33 3.47 3.55 3.28 3.55 Ho 0.76 1.12 0.72 0.75 0.76 0.72 0.76 Er 2.24 3.23 2.04 2.15 2.20 2.02 2.22 Tm 0.33 0.48 0.30 0.33 0.33 0.30 0.33 Yb 2.17 3.18 1.96 2.13 2.13 1.91 2.16 Lu 0.34 0.49 0.29 0.32 0.32 0.29 0.32 Hf 1.41 2.04 1.29 1.34 1.33 1.3 3 1.33 Ta 0.050 0.144 0.072 0.060 0.069 0.073 0.068 Pb 0.041 0.315 0.195 0.017 0.173 0.218 0.110 Th 0.117 0.122 0.050 0.059 0.066 0.043 0.081 U 0.054 0.073 0.021 0.022 0.023 0.020 0.023 208 Pb/ 204 Pb 37.877 37.894 37.731 38.12 9 37.738 9.00E 03 9.00E 03 4.63E 03 1.50E 02 4.01E 03 207 Pb/ 204 Pb 15.491 15.500 15.455 15.536 15.454 4.00E 03 3.00E 03 1.87E 03 5.00E 03 1.60E 03 206 Pb/ 204 Pb 18.389 18.451 18.394 18.531 18.404 5.00E 03 2.00E 03 2.10E 03 6.00E 03 1.90E 03 143 Nd/ 144 Nd 0.51316 0.51314 0.51315 0.51315 0.51316 7.00E 06 1.10E 05 5.70E 06 1.30E 05 6.00E 06 87 Sr/ 86 Sr 0.70258 0.70279 0.70254 0.70312 0.70253 9.00E 06 8.00E 06 8.80E 06 8.00E 06 1.20E 05 1 M ajor elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 128

128 Table B 1. Continued Sample T1013 R29 1,3 T1013 R30 1,4 T1013 R31 1 T1011 GS10 1 T1011 R01 1,3 T1011 R02 1 T1011 R03 1 T1011 R05 1 T1011 R06 1 T1011 R07 1,3,4 Seamount C C C E E E E E E E Longitude 130.531 130.535 130.535 130.437 130.437 130.441 130.441 130.441 130.441 Latitude 45.460 45.461 45.458 45.388 45.389 45. 397 45.397 45.397 45.397 Depth (m) 1836.0 1807.3 1831.2 2310.3 2294.3 2151.6 2102.2 2062.8 2042.0 Major elements (wt. %) SiO 2 49.83 48.83 49.85 50.01 50.43 50.34 50.60 50.74 50.88 50.77 TiO 2 0.92 0.82 0.93 1.25 1.05 0.98 1.40 1.12 1.43 1.33 Al 2 O 3 15.70 17.18 15.53 14.90 15.81 15.70 14.45 14.74 14.48 14.60 FeO T 9.48 8.53 9.47 9.87 9.87 9.93 10.57 10.29 10.99 10.54 MnO 0.17 0.15 0.17 0.19 0.16 0.19 0.19 0.19 0.19 0.21 MgO 8.66 9.38 8.73 7.72 8.84 8.96 7.23 7.81 6.93 7.31 CaO 12.84 12.55 12. 80 12.44 11.08 11.07 12.17 12.70 11.97 12.12 Na 2 O 2.06 2.10 2.04 2.39 2.13 2.11 2.56 2.32 2.68 2.57 K 2 O 0.03 0.04 0.04 0.10 0.07 0.06 0.12 0.07 0.14 0.11 P 2 O 5 0.06 0.06 0.05 0.10 0.07 0.06 0.11 0.08 0.12 0.11 S 0.11 0.09 0.11 0.11 0.09 0.09 0.12 0.12 0 .12 0.12 Cl 0.02 0.00 0.02 0.02 0.00 0.00 0.01 0.01 0.01 0.01 Total 99.89 99.72 99.74 99.09 99.59 99.50 99.54 100.19 99.92 99.78 Trace elements (ppm) Sc 47.6 39.6 39.6 33.4 34.5 43.1 V 252 265 251 184 181 299 Cr 373 360 385 533 549 206 Co 42.7 40.1 44.5 46.7 49.5 42.4 Ni 87.3 72.6 90.0 198.6 211.7 54.0 Cu 94.7 87.7 97.9 74.9 79.6 75.4 Zn 69.8 65.2 68.4 72.6 73.9 81.8 Ga 15.8 14.8 15.3 15.3 15.2 17.3 Rb 0.39 0.32 0.29 0.48 0.50 0.88 Sr 64 78 64 122 1 11 113 Y 24.4 25.1 22.1 19.7 19.2 30.8 Zr 41.3 46.4 40.4 44.3 44.1 81.2 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements fro m Smith et al. [1994]

PAGE 129

129 Table B 1. Continued Sample T1013 R29 1,3 T1013 R30 1,4 T1013 R31 1 T1011 GS10 1 T1011 R01 1,3 T1011 R02 1 T1011 R03 1 T1011 R05 1 T1011 R06 1 T1011 R07 1,3,4 Trace elements (ppm) Nb 0.84 1.04 0.86 1.43 1.40 2.60 Ba 4.70 5.40 3.91 7.19 6.96 11.46 La 1.32 1.20 1.34 1.35 1.75 3.20 Ce 4.39 4.45 4.25 4.46 5.04 9.95 Pr 0.83 0.87 0.82 0.83 0.90 1.64 Nd 4.89 5.17 4.83 4.91 4.99 8.76 Sm 1.96 2.14 1.97 1.91 1.96 3.09 Eu 0.80 0.83 0.79 0.80 0.83 1.16 Gd 2.98 3.03 2.95 2.69 2.74 4.22 Tb 0.57 0.57 0.57 0.50 0.52 0.78 Dy 3.83 3.73 3.84 3.19 3.26 5.15 Ho 0.84 0.82 0.83 0.68 0.69 1.09 Er 2.45 2.40 2.38 1.95 1.94 3.19 Tm 0.38 0.36 0.37 0.28 0.29 0.47 Yb 2.45 2.42 2.38 1 .83 1.84 3.07 Lu 0.37 0.36 0.36 0.27 0.27 0.49 Hf 1.35 1.49 1.34 1.32 1.35 2.18 Ta 0.050 0.072 0.066 0.095 0.102 0.170 Pb 0.001 0.190 0.225 0.220 0.281 0.214 Th 0.059 0.069 0.034 0.085 0.094 0.149 U 0.023 0.022 0.021 0.029 0. 033 0.065 208 Pb/ 204 Pb 37.904 37.770 38.044 37.798 37.850 1.60E 02 4.90E 03 1.10E 02 3.07E 03 1.00E 02 207 Pb/ 204 Pb 15.482 15.461 15.510 15.460 15.498 6.00E 03 2.07E 03 4.00E 03 1.31E 03 4.00E 03 206 Pb/ 204 Pb 18. 471 18.413 18.507 18.408 18.409 7.00E 03 2.33E 03 4.00E 03 1.48E 03 5.00E 03 143 Nd/ 144 Nd 0.51314 0.51316 0.51316 0.51319 0.51315 7.00E 06 8.90E 06 1.00E 05 1.60E 05 1.00E 05 87 Sr/ 86 Sr 0.70258 0.70258 0.70261 0.70254 0.7025 5 1.30E 05 1.30E 05 1.20E 05 1.90E 05 1.10E 05 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 130

130 T able B 1. Continued Sample T1011 R12 1,3,4 T1011 R13 1 T1011 R20 1 T1011 R27 1,3,4 T1011 R28 1 DR2 H 2,3 DR2 I 2,3 DR16 6 2,3 T1007 PC18 1 T1007 R01 1 T1007 R02 1,3,4 T1007 R06 1 Seamount E E E E E E E E E E F F Longitude 130.443 130.443 130.445 130.449 130.449 130.470 130.470 130.480 130.375 130.380 130.384 Latitude 45.402 45.402 45.405 45.412 45.412 45.370 45.370 45.390 45.321 45.324 45.326 Depth (m) 1797.7 1786.9 1766.1 1554.6 1547.8 1900.0 1900.0 1725.0 2311.8 2267.7 2093.4 Major elements (wt. % ) SiO 2 50.54 50.46 50.75 50.18 50.50 48.9 50.6 50.48 50.40 48.37 48.33 50.55 TiO 2 1.15 1.15 1.22 1.06 1.15 1.13 1.2 1.14 1.51 0.87 0.93 1.52 Al 2 O 3 14.98 14.95 14.75 15.64 14.87 15.1 14.1 14.79 14.63 18.19 18.16 14.81 FeO T 10.06 10.06 10.26 9 .68 10.03 7.8 8.34 9.92 9.82 8.03 8.13 9.66 MnO 0.18 0.18 0.16 0.16 0.18 0.18 0.17 0.17 0.17 0.15 0.14 0.19 MgO 7.68 7.79 7.63 8.30 7.94 8.2 8.01 7.95 7.40 9.34 9.33 7.37 CaO 12.72 12.68 12.77 12.60 12.71 12.7 12.1 12.81 12.29 12.23 12.26 12.31 Na 2 O 2. 37 2.39 2.39 2.25 2.34 3.24 2.92 2.38 2.72 2.35 2.37 2.69 K 2 O 0.07 0.07 0.07 0.08 0.06 0.16 0.14 0.07 0.14 0.02 0.03 0.15 P 2 O 5 0.07 0.08 0.08 0.08 0.07 0.09 0.09 0.07 0.12 0.05 0.05 0.13 S 0.11 0.12 0.12 0.10 0.11 0.12 0.11 0.09 0.09 0.11 Cl 0.02 0.0 1 0.01 0.02 0.01 0.01 0.01 0.00 0.00 0.01 Total 99.95 99.95 100.22 100.15 99.96 99.30 99.70 99.80 99.51 Trace elements (ppm) Sc 43.9 44.1 43.5 48.0 39.8 38.7 39.5 25.2 27.4 V 277 262 271 264 257 242 275 174 171 Cr 342 355 357 282 319 305 315 288 281 Co 42.3 40.5 43.9 40.8 39.4 37.1 43.3 44.2 44.6 Ni 58.0 59.5 61.0 83.2 60.9 55.6 54.6 197.3 197.0 Cu 83.5 78.7 79.9 77.9 77.3 73.3 76.0 78.1 80.3 Zn 77.3 73.6 72.5 72.2 75.0 72.9 74.3 59.1 61.9 Ga 16.7 16.3 15.9 16. 2 16.0 15.9 16.2 13.5 15.0 Rb 0.62 0.59 0.45 0.65 1.35 1.05 0.67 0.22 0.16 Sr 91 94 89 99 87 75 78 97 105 Y 27.6 25.5 24.2 26.7 26.7 25.0 25.8 19.0 19.9 Zr 61.2 55.4 57.7 59.2 62.1 63.2 62.1 38.2 46.3 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 131

131 Table B 1. Continued Sample T1011 R12 1,3,4 T1011 R13 1 T1011 R20 1 T1011 R27 1,3,4 T1011 R28 1 DR2 H 2,3 DR2 I 2,3 DR16 6 2,3 T1007 PC18 1 T1007 R01 1 T1007 R02 1,3,4 T1007 R06 1 Trace elements (ppm) Nb 1.50 1.44 1.38 1.69 1.26 1.28 1.35 0.49 0.50 Ba 6.51 7.54 6.29 8.14 8.34 6.73 9.64 3.14 1.96 La 2.06 1.91 2.01 2.23 2.07 1.96 2.05 0.95 1.12 Ce 6.90 6.21 6.26 6.94 6.46 6.17 7.17 3.84 4.60 Pr 1.21 1.12 1.14 1.21 1.21 1.17 1.21 0.81 0.92 Nd 6.74 6.47 6.32 6.59 7.16 7.00 7.15 5.06 5.58 Sm 2.56 2.50 2.39 2.40 2.46 2.38 2.44 1.99 2.05 Eu 1.00 0.95 0.93 0.95 0.95 0 .90 0.91 0.80 0.85 Gd 3.64 3.50 3.42 3.46 3.65 3.49 3.53 2.71 2.95 Tb 0.67 0.67 0.65 0.65 0.68 0.66 0.67 0.51 0.53 Dy 4.44 4.42 4.28 4.28 4.38 4.19 4.33 3.23 3.45 Ho 0.95 0.94 0.92 0.92 0.93 0.90 0.92 0.68 0.72 Er 2.74 2.71 2.63 2.65 2. 68 2.57 2.68 1.93 2.08 Tm 0.42 0.41 0.40 0.41 0.42 0.39 0.41 0.29 0.31 Yb 2.76 2.65 2.60 2.64 2.64 2.50 2.53 1.84 1.94 Lu 0.42 0.39 0.39 0.40 0.41 0.38 0.39 0.27 0.30 Hf 1.76 1.80 1.73 1.76 1.84 1.89 1.80 1.35 1.44 Ta 0.100 0.100 0.104 0 .110 0.140 0.130 0.100 0.040 0.040 Pb 0.096 0.083 0.275 0.104 0.130 0.090 0.630 0.191 0.018 Th 0.086 0.083 0.087 0.105 0.090 0.090 0.170 0.055 0.025 U 0.047 0.044 0.041 0.062 0.060 0.050 0.050 0.011 0.015 208 Pb/ 204 Pb 37.803 3 7.687 37.823 37.442 37.479 3.00E 03 2.63E 03 1.10E 02 2.92E 03 1.00E 02 207 Pb/ 204 Pb 15.489 15.455 15.496 15.444 15.456 1.00E 03 1.03E 03 4.00E 03 1.30E 03 3.00E 03 206 Pb/ 204 Pb 18.395 18.366 18.373 18.118 18.119 1.00E 03 1.12E 03 4.00E 03 1.46E 03 4.00E 03 143 Nd/ 144 Nd 0.51315 0.51318 0.51316 0.51320 0.51318 7.00E 06 6.20E 06 7.00E 06 8.70E 06 1.20E 05 87 Sr/ 86 Sr 0.70258 0.70258 0.70267 0.70243 0.70252 1.10E 05 6.10E 06 1.0 0E 05 1.80E 05 1.00E 05 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 132

132 Table B 1. Continued Samp le T1007 R16 1,3,4 T1007 R17 1,3,4 T1007 R18 1,3 DR1 A1 2,3 DR1 D1 2,3 T1014 R04 1,3,4 T1014 R08 1 T1014 R10 1 T1014 R13 1,3,4 T1014 R15 1 T1014 R16 1 Seamount F F F F F G G G G G G Longitude 130.391 130.397 130.397 130.380 130.380 130.335 130.338 130.3 40 130.344 130.347 130.347 Latitude 45.339 45.341 45.342 45.330 45.330 45.286 45.287 45.289 45.290 45.291 45.291 Depth (m) 2187.6 2107.0 2071.4 2135.0 2135.0 2357.6 2379.5 2366.0 2361.4 2326.1 2319.7 Major elements (wt. %) SiO 2 48.84 48.68 48 .78 49.5 49.3 50.71 50.74 50.83 50.32 50.28 50.82 TiO 2 1.30 1.24 1.25 1.45 1.43 1.34 1.27 1.35 1.19 1.31 1.39 Al 2 O 3 16.97 17.13 17.26 14.6 14.8 14.58 14.60 14.56 15.20 14.79 14.54 FeO T 8.88 8.60 8.65 8.52 8.44 10.23 10.16 10.05 9.61 9.98 10.07 MnO 0.14 0.14 0.16 0.18 0.16 0.17 0.18 0.18 0.18 0.17 0.19 MgO 8.75 8.88 8.78 7.67 8.02 7.45 7.42 7.42 7.92 7.49 7.47 CaO 11.90 11.90 11.94 12.3 12 12.18 12.19 12.31 12.47 12.47 12.27 Na 2 O 2.71 2.69 2.76 3.04 3.09 2.58 2.59 2.58 2.47 2.57 2.56 K 2 O 0.06 0.06 0. 05 0.16 0.16 0.11 0.11 0.11 0.10 0.10 0.11 P 2 O 5 0.10 0.08 0.09 0.136 0.12 0.12 0.10 0.11 0.09 0.11 0.12 S 0.10 0.10 0.10 0.11 0.12 0.11 0.11 0.12 0.11 Cl 0.00 0.00 0.01 0.00 0.01 0.00 0.01 0.01 0.01 Total 99.76 99.50 99.81 99.58 99.48 99.60 99.68 99.40 99.67 Trace elements (ppm) Sc 33.5 38.5 39.5 42.6 43.0 53.1 45.5 46.1 42.2 V 214 204 206 286 279 296 297 305 279 Cr 510 496 446 272 271 186 190 194 339 Co 44.8 44.4 42.3 38.1 37.1 40.5 41.5 42.7 41.3 Ni 241.6 238.1 190.4 56.7 56.7 57.7 56.8 57.4 82.0 Cu 73.3 74.1 74.6 82.5 78.6 76.2 76.5 77.5 84.3 Zn 66.4 63.9 63.9 79.7 78.3 78.1 77.6 78.9 76.0 Ga 15.9 15.5 15.9 16.9 16.8 17.2 17.2 17.3 16.4 Rb 0.36 0.41 0.40 0.93 1.00 0.91 0.91 0.95 0.82 Sr 138 141 145 132 131 123 132 132 124 Y 26.9 25.7 26.0 32.4 31.0 30.6 29.8 30.2 28.3 Zr 79.1 75.2 75.7 96.2 93.6 80.8 76.3 77.3 76.5 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from C ornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 133

133 Table B 1. Continued Sample T1007 R16 1,3,4 T1007 R17 1,3,4 T1007 R18 1,3 DR1 A1 2,3 DR1 D1 2,3 T1014 R04 1,3,4 T1014 R08 1 T1014 R10 1 T1014 R13 1,3,4 T1014 R15 1 T1014 R16 1 Trace elements (ppm ) Nb 1.30 1.21 1.19 2.44 2.28 2.44 2.42 2.46 2.21 Ba 4.78 5.35 5.26 11.23 11.51 11.25 12.41 12.12 10.26 La 2.25 2.22 2.24 3.32 3.33 3.13 3.07 3.12 2.83 Ce 8.27 7.80 7.86 10.36 10.28 9.62 9.35 9.56 8.86 Pr 1.49 1.43 1.45 1.82 1.80 1.6 3 1.62 1.63 1.52 Nd 8.18 7.92 7.95 9.89 9.88 8.67 8.69 8.82 8.34 Sm 2.86 2.78 2.78 3.23 3.27 2.98 3.09 3.13 2.83 Eu 1.09 1.06 1.08 1.20 1.18 1.14 1.17 1.17 1.07 Gd 3.77 3.63 3.67 4.38 4.35 4.13 4.18 4.20 3.88 Tb 0.67 0.66 0.67 0.79 0.80 0.75 0.79 0.78 0.72 Dy 4.30 4.17 4.24 5.21 5.16 4.96 5.04 5.02 4.64 Ho 0.92 0.88 0.89 1.07 1.08 1.06 1.05 1.07 0.99 Er 2.57 2.49 2.52 3.11 3.12 3.03 3.08 3.09 2.85 Tm 0.39 0.37 0.38 0.48 0.47 0.47 0.47 0.46 0.43 Yb 2.51 2.39 2.43 3.07 3.01 2.98 3.00 3.01 2.76 Lu 0.38 0.36 0.37 0.47 0.47 0.46 0.46 0.45 0.42 Hf 2.10 2.03 2.08 2.53 2.50 2.24 2.28 2.26 2.09 Ta 0.090 0.090 0.080 0.200 0.190 0.170 0.167 0.167 0.140 Pb 0.167 0.170 0.189 0.270 0.270 0.084 0.401 0.390 0.099 Th 0.070 0.077 0 .075 0.150 0.150 0.144 0.174 0.170 0.117 U 0.034 0.029 0.030 0.070 0.070 0.062 0.063 0.063 0.054 208 Pb/ 204 Pb 37.734 37.744 37.596 37.788 37.691 37.670 37.844 1.00E 02 1.50E 02 1.60E 03 9.00E 03 2.10E 03 1.46E 03 8.00E 03 207 Pb/ 204 Pb 15.482 15.485 15.446 15.490 15.462 15.456 15.500 4.00E 03 5.00E 03 6.24E 04 3.00E 03 7.50E 04 5.99E 04 2.00E 03 206 Pb/ 204 Pb 18.311 18.314 18.276 18.341 18.324 18.319 18.347 4.00E 03 6.00E 03 7.49E 04 3.00E 03 8.20E 04 6.86E 04 2.00E 03 143 Nd/ 144 Nd 0.51317 0.51317 0.51320 0.51315 0.51316 0.51319 0.51313 9.00E 06 9.00E 06 6.70E 06 9.00E 06 4.60E 06 9.60E 06 1.30E 05 87 Sr/ 86 Sr 0.70247 0.70249 0.70238 0.70257 0.70245 0.70247 0.70252 1.00E 05 1.00E 05 1.60E 05 1.00E 05 4.50E 05 2.60E 05 1.10E 05 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 134

134 Table B 1. C ontinued Sample T1014 R17 1,3 T1014 R18 1,3,4 T1014 R19 1 T1014 R22 1,3,4 T1014 R23 1 T1014 R24 1 DR14 1 DR12A 2 DR12A 2 2 DR12A 6 2 DR12B 2,5 DR12B 4 2 Seamount G G G G G G Ridge Ridge Ridge Ridge Ridge Ridge Longitude 130.347 130.348 130.353 130.353 1 30.353 130.353 130.480 130.140 130.140 130.140 130.140 130.140 Latitude 45.291 45.292 45.294 45.294 45.294 45.294 45.390 45.170 45.170 45.170 45.170 45.170 Depth (m) 2322.4 2310.5 2286.8 2298.1 2288.5 2284.3 1725.0 2380.0 2380.0 2380.0 2380.0 2380.0 Maj or elements (wt. %) SiO 2 50.88 50.22 50.71 50.76 50.59 50.56 50.21 50.16 49.87 50.12 50.06 50.12 TiO 2 1.37 1.34 1.31 1.28 1.25 1.29 1.09 1.21 1.25 1.21 1.21 1.23 Al 2 O 3 14.56 15.03 14.56 14.57 14.49 14.57 15.06 15.63 15.69 15.69 15.56 15.60 F eO T 10.04 9.75 10.12 10.00 10.05 10.07 9.66 9.35 9.41 9.39 9.35 9.34 MnO 0.17 0.16 0.18 0.20 0.18 0.20 0.16 0.20 0.21 0.21 0.25 0.16 MgO 7.43 7.74 7.43 7.42 7.40 7.44 8.16 8.02 8.13 8.23 8.33 8.39 CaO 12.22 12.42 12.26 12.26 12.30 12.26 13.12 12.60 12.5 4 12.48 12.54 12.48 Na 2 O 2.57 2.57 2.56 2.56 2.56 2.53 2.16 2.36 2.36 2.33 2.34 2.40 K 2 O 0.11 0.10 0.12 0.11 0.11 0.12 0.05 0.08 0.09 0.08 0.08 0.11 P 2 O 5 0.13 0.10 0.10 0.11 0.10 0.10 0.08 S 0.12 0.11 0.11 0.11 0.11 0.11 0.10 Cl 0.01 0.00 0. 01 0.00 0.00 0.00 0.00 Total 99.60 99.54 99.46 99.38 99.14 99.23 Trace elements (ppm) Sc 52.9 43.7 52.9 36.0 39.9 39.3 38.6 V 296 281 293 231 270 273 261 Cr 185 344 185 362 345 407 338 Co 39.5 40.9 39.2 38.0 40 .2 38.8 Ni 55.5 83.0 55.6 73.3 95.8 94.1 Cu 74.9 76.2 75.4 78.9 67.9 65.9 Zn 76.6 73.2 77.4 71.2 70.5 68.6 Ga 17.2 16.4 17.1 17.4 15.0 14.2 Rb 0.87 0.65 0.91 0.37 0.95 0.92 Sr 122 130 122 72 117 112 Y 28.4 29.7 28.6 23.9 27.3 26.2 Zr 80.5 79.2 80.1 53.9 70.9 71.1 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [19 94]

PAGE 135

135 Table B 1. Continued Sample T1014 R17 1,3 T1014 R18 1,3,4 T1014 R19 1 T1014 R22 1,3,4 T1014 R23 1 T1014 R24 1 DR14 1 DR12A 2 DR12A 2 2 DR12A 6 2 DR12B 2,5 DR12B 4 2 Trace elements (ppm) Nb 2.45 1.94 2.44 0.84 2.72 2.68 Ba 11.24 6.59 11.05 5.48 11.25 20.53 10.77 La 3.05 2.95 3.05 1.66 3.01 2.95 Ce 9.43 9.03 9.40 5.29 8.76 8.57 Pr 1.60 1.51 1.61 1.03 1.46 1.42 Nd 8.46 8.51 8.49 6.31 7.86 7.59 Sm 2.96 2.97 2.93 2.08 2.69 2.64 Eu 1.12 1.09 1 .11 0.82 0.99 0.99 Gd 4.05 3.94 4.01 3.18 3.55 3.53 Tb 0.73 0.74 0.73 0.60 0.68 0.67 Dy 4.87 4.84 4.79 3.78 4.36 4.29 Ho 1.03 1.02 1.03 0.82 0.94 0.92 Er 2.97 2.95 2.96 2.34 2.70 2.68 Tm 0.45 0.45 0.45 0.36 0.40 0.39 Yb 2.91 2.92 2.90 2.23 2.68 2.65 Lu 0.44 0.44 0.44 0.34 0.40 0.39 Hf 2.24 2.16 2.21 1.55 1.96 1.98 Ta 0.160 0.130 0.160 0.080 0.178 0.175 Pb 0.190 0.238 0.163 0.040 0.334 0.321 Th 0.099 0.118 0.120 0.070 0.145 0.146 U 0.060 0.052 0.060 0.040 0.061 0.060 208 Pb/ 204 Pb 37.827 37.695 37.753 37.756 1.80E 02 8.00E 03 2.08E 03 2.14E 03 207 Pb/ 204 Pb 15.491 15.460 15.461 15.462 5.00E 03 3.00E 03 8.59E 04 8.87E 04 206 Pb/ 204 Pb 18.387 18.325 18.430 18.432 5.00E 03 3.00E 03 8.97E 04 1.04E 03 143 Nd/ 144 Nd 0 .51314 0.51315 0.51317 0.51315 1.30E 05 7.00E 06 7.40E 06 5.40E 06 87 Sr/ 86 Sr 0.70259 0.70268 0.70253 0.70249 9.00E 06 1.20E 05 1.50E 05 1.20E 05 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 136

136 Table B 1. Continued Sample DR12B 5 2,5 DR17 2 DR17 2 2,5 DR18 2,5 DR18 2 2,5 DR18 3 2 DR18 5 2 Seamount Ridge Ridge Ridge Ridge Ridge Ridge Ridge Longitude 130.140 130.080 130.080 130.070 130.070 130.070 130.070 Latitude 45.170 45.330 45.330 45.320 45.320 45.320 45.320 Depth (m) 2380.0 2430.0 2430.0 2410.0 2410.0 2410.0 2410.0 Major elements (wt. %) SiO 2 50.04 50.6 0 50.53 50.51 50.23 50.69 50.69 TiO 2 1.20 1.60 1.57 1.60 1.61 1.57 1.57 Al 2 O 3 15.57 14.55 14.52 14.58 14.51 14.47 14.47 FeO T 9.41 10.60 10.73 10.69 10.55 10.66 10.66 MnO 0.18 0.22 0.22 0.23 0.21 0.21 0.21 MgO 8.37 7.37 7.29 7.37 7.32 7.30 7.30 CaO 12 .52 12.18 12.18 12.33 12.11 12.06 12.06 Na 2 O 2.35 2.50 2.43 2.45 2.48 2.49 2.49 K 2 O 0.08 0.16 0.13 0.13 0.17 0.17 0.17 P 2 O 5 S Cl Total Trace elements (ppm) Sc 42.6 42.8 46.8 47.8 40.1 44.3 44.2 V 275 335 313 321 3 08 343 347 Cr 382 248 333 335 293 233 255 Co 41.9 39.1 38.4 40.2 37.9 40.9 40.1 Ni 89.9 61.4 64.4 67.3 57.7 61.9 62.0 Cu 68.9 63.3 64.9 64.5 62.2 65.1 65.0 Zn 69.0 83.0 74.5 74.0 74.1 87.0 85.1 Ga 17.5 16.5 19.3 18.7 18.6 17.8 17.3 Rb 1.95 1.54 3.25 1.82 0.61 1.67 1.60 Sr 118 111 115 118 116 122 116 Y 25.1 36.0 30.4 30.8 30.9 37.3 37.7 Zr 74.8 98.0 93.7 94.1 89.9 94.8 93.9 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ra tios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 137

137 Table B 1. Continued Sample DR12B 5 2,5 DR17 2 DR17 2 2,5 DR18 2,5 DR18 2 2,5 DR18 3 2 DR18 5 2 Trace elements (ppm) Nb 3.00 4.56 3.93 4.19 3.81 4.91 4.75 Ba 16.65 16.99 32.26 38.36 35.97 19.30 18.05 La 4.30 4.63 4.47 Ce 12.11 12.89 12.62 Pr 1.98 2.10 2.04 Nd 10.21 10.90 10.58 Sm 3.57 3.71 3.66 Eu 1.24 1.31 1.28 Gd 4.60 4.87 4.80 Tb 0.89 0.93 0.91 Dy 5.78 6.03 5.98 Ho 1.23 1.29 1.28 Er 3.62 3.78 3.70 Tm 0.54 0.56 0.56 Yb 3.58 3.74 3.69 Lu 0.54 0.56 0.56 Hf 2.70 2.63 2.63 Ta 0.284 0.307 0.297 Pb 0.436 0.471 0.448 Th 0.249 0.239 0.246 U 0.103 0.112 0.106 208 Pb/ 204 Pb 37.800 37.800 37.794 1.80E 03 1.64E 03 1.82E 03 207 Pb/ 204 Pb 15.465 15.463 15.462 7.55E 04 6.39E 04 6.66E 04 206 Pb/ 204 Pb 18.474 18.468 18.468 8.38E 04 8.02E 04 7.59E 04 143 Nd/ 144 Nd 0.51315 0.51316 0.51314 5.70E 06 9.60E 06 1.00E 05 87 Sr/ 86 Sr 0.70252 0.70247 0.70248 1.10E 05 1.20E 05 1.10E 05 1 Major elements from Wendt [2008] 2 Major elements from Smith et al. [1994] 3 Trace elements from Wendt [2008] 4 Isotopic ratios from Cornejo [2008] 5 Trace elements from Smith et al. [1994]

PAGE 138

138 APPENDIX C MAJOR ELEMENT, TRACE ELEMENT, AND ISOTOPI C RATIOS OF JDFR OFF AXIS BASALT S

PAGE 139

139 Table C 1. Major element, trace element, and isotopic analyses of seamount basalts along the southern JdFR Sample DR7A DR7D 95DR1 1 1 95DR1 3 1 95DR1 5 1 94DR2 1 1 94DR2 5 1 94DR4 2 1 94DR4 5 1 94DR5 1 1 94DR5 3 1 DR5 B 1 DR5 F 1 DR14 1 1 DR15 1 1 Seamount Jinja Jinja Unnamed Unnamed Unnamed Unnamed Unnamed Unnamed Unnamed Unnamed Unnamed Vance OA Vance OA Vance OA VanceOA Major elements (wt. %) SiO 2 51.24 51.27 51.11 51.08 50.99 51.19 50.98 51.18 51.18 50.78 50.47 48.8 47.7 50.21 49.64 TiO 2 1.23 1.19 0.99 0.99 0.99 1.17 1.14 1.35 1.35 1.69 1.75 1.38 1.37 1.09 1.27 Al 2 O 3 14.1 14.35 14.95 15.1 15.04 14.5 14.31 13.92 14.02 13.52 13.38 14.9 15.2 15.06 16.36 FeOT 10.32 9.8 8.76 8.78 8.81 9.54 9.55 10.36 10.43 11.6 11.89 8.13 8.18 9.66 8.84 MnO 0.18 0.18 0.16 0.15 0.16 0.18 0.17 0.19 0.19 0.2 0.2 0.16 0.16 0.16 0.15 MgO 7.74 8.1 8.67 8.72 8.67 8.09 8.11 7.91 8 7.24 7.03 8.11 7.87 8.16 8.62 CaO 11.99 1 2.25 12.69 12.71 12.71 12.67 12.7 12.21 12.23 11.52 11.37 12.1 11.9 13.12 12.35 Na 2 O 2.4 2.34 2.11 2.12 2.12 2.37 2.27 2.16 2.19 2.35 2.37 3.04 4.08 2.16 2.31 K 2 O 0.08 0.07 0.03 0.03 0.03 0.05 0.05 0.05 0.05 0.09 0.08 0.24 0.26 0.05 0.09 P 2 O 5 0.1 0.09 0 .07 0.07 0.07 0.09 0.09 0.12 0.11 0.15 0.15 0.13 0.14 0.08 0.12 S 0.07 0.06 0.06 0.06 0.06 0.07 0.07 0.08 0.08 0.08 0.08 0.1 0.09 Cl 0.01 0.01 0 0 0 0.02 0.02 0 0.01 0.01 0.01 0 0 Total 99.57 99.82 99.7 99.89 99.73 100.03 99.56 99.66 99.98 99.34 98. 89 96.99 96.86 99.87 99.84 Trace elements (ppm) Sc 44 41.7 42.6 39 39 42.4 40 42.1 42.8 43.3 43 39 37.9 36 32.7 V 305 285 365 254 252 281 265 303 317 330 368 256 251 231 223 Cr 140 242 204 428 430 359 359 292 194 196 203 319 313 362 313 Co 42.8 40.5 44.7 41.3 41 42.1 42.2 40 41.7 43.2 43.2 36.8 36.7 38 37.2 Ni 52.2 67.6 54.5 103.2 99.3 69.6 74.1 82.1 53.1 52.7 54.5 72.8 69.5 73.3 115 Cu 75.7 74.2 61.5 81.6 79.9 88.6 87.9 70.7 70 68.9 62.2 67.4 68.6 78.9 69.5 Zn 78.6 71.8 93.9 80.9 76.5 75.3 74.9 85.2 88.2 82.8 96.6 73.7 71.4 71.2 71.4 Ga 15.6 15.8 18 14.8 15.1 15.7 15.5 16.6 16.5 16.7 18 16.5 16.5 17.4 15.4 Rb 0.89 0.76 0.86 0.35 0.28 0.46 0.42 0.98 0.67 0.66 0.89 1.75 1.72 0.37 0.68 Sr 89 101 65 67 70 82 81 114 58 60 65 142 139 72 9 7 Y 29.1 27.7 41.4 22 23.4 26.5 24.7 33.6 33.2 34.3 41.9 28.4 27.8 23.9 24.7 Zr 66 62.7 95.4 53.9 48.2 59.6 55.7 92.7 75.6 75.1 104.8 91.1 86 53.9 69.9 Nb 2.16 2.18 2.32 0.7 0.67 1.29 1.18 2.46 1.84 1.84 2.44 4.46 4.32 0.84 1.71 Ba 9.54 9.48 9.46 7.25 3.59 5.21 4.96 9.08 6.25 6.72 12.37 21.18 20.48 5.48 7.16 La 2.72 2.25 3.1 1.34 1.48 1.95 1.81 3.45 2.41 2.59 3.14 3.97 3.88 1.66 2.52 Ce 7.96 7.07 9.93 4.76 5.08 6.51 6.03 10.83 7.9 8.28 10.2 11.01 10.88 5.29 7.68 Pr 1.38 1.25 1.75 0.92 0.96 1.19 1.1 1 .85 1.41 1.48 1.79 1.84 1.79 1.03 1.4 Nd 7.46 6.92 9.97 5.51 5.72 6.83 6.31 10.06 8.11 8.45 10.16 9.73 9.59 6.31 8.07 1 Trace element analyses from Wendt [2008]

PAGE 140

140 Table C 1. Continued Sample DR7A DR7D 95DR1 1 1 95DR1 3 1 95DR1 5 1 94DR2 1 1 94DR2 5 1 94DR4 2 1 94DR4 5 1 94DR5 1 1 94DR5 3 1 DR5 B 1 DR5 F 1 DR14 1 1 DR15 1 1 Trace elements (ppm) Sm 2.7 2.63 3.59 2.01 2.11 2.44 2.24 3.4 2.98 3.09 3.66 3.12 3.07 2.08 2.57 Eu 1 0.99 1.25 0.8 0.85 0.95 0.88 1.25 1.06 1.11 1.28 1.16 1.13 0.82 0.97 Gd 3.6 8 3.54 5.09 2.97 3.09 3.47 3.24 4.6 4.29 4.37 5.24 4.16 4.08 3.18 3.71 Tb 0.71 0.66 0.98 0.57 0.59 0.66 0.61 0.85 0.82 0.85 1.02 0.76 0.73 0.6 0.7 Dy 4.7 4.33 6.44 3.72 3.86 4.3 4.02 5.62 5.46 5.61 6.72 4.77 4.71 3.78 4.22 Ho 1.02 0.93 1.42 0.79 0.85 0. 93 0.87 1.2 1.19 1.24 1.45 1 0.96 0.82 0.9 Er 2.96 2.7 4.11 2.32 2.44 2.68 2.5 3.43 3.44 3.51 4.18 2.85 2.81 2.34 2.55 Tm 0.44 0.41 0.64 0.34 0.36 0.4 0.38 0.51 0.52 0.54 0.64 0.43 0.43 0.36 0.39 Yb 2.95 2.67 4.06 2.27 2.3 2.65 2.48 3.39 3.42 3.52 4.23 2.76 2.7 2.23 2.4 Lu 0.44 0.4 0.63 0.35 0.36 0.4 0.37 0.52 0.53 0.55 0.66 0.42 0.41 0.34 0.38 Hf 1.93 1.87 2.75 1.59 1.52 1.74 1.65 2.6 2.22 2.31 3.03 2.48 2.35 1.55 2 Ta 0.144 0.143 0.16 0.05 0.05 0.09 0.08 0.18 0.12 0.13 0.16 0.34 0.33 0.08 0.16 Pb 0 .323 0.327 0.1 0.06 0.02 0.01 0.02 0.21 0.04 0.05 0.15 0.25 0.26 0.04 0.1 Th 0.136 0.138 0.125 0.024 0.036 0.064 0.058 0.136 0.074 0.109 0.133 0.28 0.28 0.07 0.13 U 0.058 0.052 0.063 0.028 0.022 0.033 0.031 0.058 0.049 0.053 0.063 0.11 0.11 0.04 0.0 5 208 Pb/ 204 Pb 37.845 37.865 2.13E 03 2.29E 03 207 Pb/ 204 Pb 15.461 15.461 9.02E 04 8.13E 04 206 Pb/ 204 Pb 18.472 18.487 9.42E 04 9.53E 04 143 Nd/ 144 Nd 0.51305 0.51318 7.10E 06 5.90E 06 87 Sr/ 86 Sr 0.70257 0.70244 1.10E 05 9.20E 06 1 Trace element analyses from Wendt [2008]

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141 Table C 1. Continued Sample DR9 A DR9 B DR9 C 62DR 1 62DR 2 62DR 2E 62DR 3A 62DR 4A 62DR 5A 62DR 6A 461 G1 6 461 G17 461 G18 461 G20 T461 G21 Seamount Hacksaw Hacksaw Hacksaw Rogue Rogue Rogue Rogue Rogue Rogue Rogue Unnamed Unnamed Unnamed Unnamed Unnamed Major elements (ppm) SiO 2 50.68 50.24 50.24 49.71 50.08 50.57 49.99 49.97 50.08 50.1 48.8 48.45 48.58 48.5 48.16 TiO 2 1.03 1.03 1.18 1.5 0.93 0.84 0.71 0.7 0.7 0.66 1.02 1.08 1.06 0.92 0.89 Al 2 O 3 14.6 14.62 14.75 14.56 15.21 14.35 14.92 14.96 14.76 14.84 16.56 16.3 16.32 17 17.65 FeOT 10.05 10.11 10.4 10.95 9.42 9.86 9.13 9.06 9.15 9.2 8.31 8.54 8.32 8.3 7.93 MnO 0.2 0.17 0.16 0.15 0.16 0.15 0.16 0.16 0.19 0.18 0.16 0.15 MgO 8.09 8.16 7.76 7.45 8.52 8.63 9.34 9.24 9.32 9.4 9.73 10.06 10 9.77 9.72 CaO 13.08 13.05 12.52 12.12 13.29 13.61 13.76 13.8 13.74 13.85 12.32 12.14 12.31 12.23 12. 37 Na 2 O 2.03 2.06 2.28 2.91 1.94 1.72 1.64 1.63 1.67 1.63 2.17 2.22 2.18 2.14 2.17 K 2 O 0.06 0.07 0.09 0.18 0.08 0.05 0.04 0.03 0.04 0.03 0.09 0.08 0.08 0.09 0.07 P 2 O 5 0.08 0.09 0.13 0.13 0.07 0.06 0.04 0.04 0.03 0.05 0.09 0.1 0.09 0.09 0.06 S Cl Total 99.7 99.43 99.35 99.7 99.71 99.84 99.71 99.6 99.64 99.92 99.25 99.16 99.12 99.19 99.17 Trace elements (ppm) Sc 42.4 45.7 40.1 39.7 41.5 40.7 41.6 30.2 32.1 33 32.1 30.6 V 264 300 256 256 271 252 252 19 9 199 214 204 194 Cr 235 248 437 396 443 467 463 421 466 470 406 435 Co 40.3 46 43 42.7 42.7 45.6 44 39.3 40.8 42.3 40.1 39.7 Ni 62.5 68.8 93.4 105 89.1 98.5 98 188.5 202.2 239.3 177 203.2 Cu 79.4 86.2 98.6 86.2 89.4 101.9 100.5 64.4 65.1 7 5.9 66.5 79.6 Zn 70.9 77.4 65 69.2 69.2 65.5 64.7 56.1 57.2 69.6 57.2 67.2 Ga 14.9 16.1 12.6 14.3 13.8 13.5 13.4 13.7 13.6 15.5 14.1 14.6 Rb 0.37 0.41 0.26 0.51 0.09 0.08 0.07 0.35 0.31 0.43 0.41 0.34 Sr 65 70 34 61 36 33 33 116 117 115 121 102 Y 24.2 25.8 19.1 19.7 17.9 19.7 19.6 21.3 22.1 22.4 21.6 19.8 Zr 40.1 42.7 29.1 42.4 30.2 25.5 25.2 52.8 56 67.8 54.1 60.4 Nb 0.81 0.88 0.37 1.35 0.38 0.31 0.3 1.54 1.33 1.05 1.65 0.68 Ba 4.49 6.92 1.66 5.42 0.88 0.67 0.6 6.23 4.7 5.22 6.51 3.77 La 1.28 1.4 0.9 1.59 0.83 0.73 0.74 1.72 1.63 2.2 1.81 1.88 Ce 4.33 4.7 2.82 4.6 2.77 2.39 2.41 5.78 5.69 7.62 5.89 6.69 Pr 0.84 0.91 0.56 0.82 0.58 0.51 0.52 1.03 1.05 1.35 1.05 1.21 Nd 5.04 5.43 3.47 4.6 3.52 3.16 3.19 5.58 5.7 5 6.78 5.94 5.86 1 Trace element analyses from Wendt [2008]

PAGE 142

142 Table C 1. Continued Sample DR9 A DR9 B DR9 C 62DR 1 62DR 2 62DR 2E 62DR 3A 62DR 4A 62DR 5A 62DR 6A 461 G16 461 G17 461 G18 461 G20 T461 G21 Trace elements (ppm) Sm 2.03 2. 19 1.43 1.79 1.53 1.4 1.44 2.04 2.11 2.3 2.13 2.02 Eu 0.81 0.86 0.58 0.71 0.62 0.6 0.59 0.81 0.84 0.93 0.84 0.84 Gd 3.02 3.28 2.25 2.72 2.4 2.24 2.27 2.7 2.85 3.55 2.88 3.32 Tb 0.59 0.63 0.44 0.54 0.48 0.46 0.46 0.51 0.54 0.62 0.53 0.58 Dy 3 .91 4.19 3.01 3.59 3.29 3.12 3.19 3.29 3.51 3.79 3.43 3.41 Ho 0.85 0.91 0.68 0.78 0.73 0.69 0.69 0.71 0.74 0.81 0.74 0.71 Er 2.49 2.69 2.02 2.27 2.11 2.01 2.02 2.06 2.16 2.1 2.16 1.83 Tm 0.39 0.41 0.3 0.35 0.33 0.32 0.31 0.31 0.32 0.39 0.32 0.37 Yb 2.48 2.64 2.02 2.25 2.17 2.05 2 2.05 2.06 2.34 2.08 2.08 Lu 0.38 0.4 0.3 0.35 0.33 0.32 0.32 0.31 0.31 0.36 0.32 0.32 Hf 1.41 1.47 0.98 1.34 1.05 0.89 0.91 1.49 1.5 1.73 1.5 1.53 Ta 0.063 0.066 0.03 0.097 0.036 0.031 0.031 0.105 0.0 89 0.09 0.11 0.07 Pb 0.076 0.219 0.076 0.212 0.101 0.22 0.142 0.3 0.289 0.317 0.307 0.272 Th 0.075 0.072 0.021 0.093 0.02 0.027 0.028 0.093 0.078 0.078 0.099 0.06 U 0.019 0.024 0.012 0.049 0.013 0.01 0.009 0.036 0.028 0.039 0.039 0.032 208 Pb/ 204 Pb 37.627 37.66 37.556 37.55 37.297 37.565 37.491 37.684 37.679 1.83E 03 2.89E 03 4.30E 03 3.72E 03 4.20E 03 6.98E 03 5.25E 03 2.13E 03 2.00E 03 207 Pb/ 204 Pb 15.448 15.451 15.418 15.415 15.371 15.446 15.42 15.461 15. 463 7.20E 04 1.19E 03 1.80E 03 1.47E 03 1.70E 03 2.92E 03 2.11E 03 8.44E 04 9.14E 04 206 Pb/ 204 Pb 18.227 18.267 18.177 18.145 17.933 18.147 18.107 18.415 18.403 1.22E 03 1.47E 03 2.10E 03 1.75E 03 2.00E 03 3.05E 03 2.45E 03 9.96E 0 4 1.14E 03 143 Nd/ 144 Nd 0.51317 0.5132 0.51326 0.51329 0.51331 0.51324 0.51326 0.51317 0.51316 0.51322 6.10E 06 8.10E 06 1.60E 05 5.80E 06 1.00E 05 1.00E 05 6.00E 06 6.30E 06 6.20E 06 1.00E 05 87 Sr/ 86 Sr 0.70249 0.70243 0.70241 0.70231 0.7 0207 0.70235 0.70231 0.70242 0.70247 0.70231 1.50E 05 2.30E 05 1.10E 05 1.10E 05 1.80E 05 1.30E 05 8.50E 06 1.40E 05 9.50E 06 1.40E 05 1 Trace element analyses from Wendt [2008]

PAGE 143

143 Table C 2. Model parameters for DMM HIMU mixing models D ehydrated bulk oceanic crust 3% batch melt of oceanic crust Depleted Rogue basalt Clinopyroxene partition coefficients Garnet partition coefficients Bulk D 82% Cpx 12% Gnt Rb 1.43 1 43.46 0.09 0.0035 1 0.0007 1 0.002996 Sr 125 1 1567.18 35.9 0.08 1 0.00 5 1 0.0513 Sm 3.02 1 10.66 1.53 0.3 1 0.27 1 0.26122 Nd 9.05 1 52.11 3.51 0.16 1 0.056 1 0.14183 Nb 2 2 52.40 0.382 0.021 3 0.008 3 0.00842 Zr 64.7 2 303.56 30.21 0.093 3 0.4 3 0.1888 87 Sr/ 86 Sr 0.70255 .7032 2 0.70255 .7032 0.70207 143 Nd/ 144 Nd 0.5 1288 2 0.51288 0.51331 1 Hanyu et al. [2011] 2 Stracke and Bourdon [2009] 3 Klemme et al. [2002]

PAGE 144

144 APPENDIX D TRACE ELEMENT AND IS OTOPIC RATIOS OF LAM ONT SEAMOUNT BASALTS

PAGE 145

145 Table D 1. Trace element and isotopic ratios of basalts from the Lamont seamo unt chain Sample 1571 1936 1572 1727 1572 1755 1561 1622 1562 2112 1564 1857 1564 2128 1564 2255 1565 1642 1565 1724 1570 1626 1570 1949 F5 1a F7 4 F9 1 Seamount NEW DTD DTD MOK MOK MOK MOK MOK MOK MOK MOK MOK MOK MOK MOK Sc 36.9 34.8 32.2 28.4 42.6 30.0 36.7 38.2 35.4 35.9 32.0 37.1 32.1 42.3 34.6 V 245 212 206 188 261 195 231 234 221 223 211 225 209 294 215 Cr 297 308 289 286 343 318 342 354 351 350 322 340 314 136 419 Co 40.7 43.9 40.1 45.1 42.9 42.8 44.8 46.9 46.7 46.9 44.2 43.8 38.8 46.1 45.5 Ni 71.5 117.3 109.6 157.8 60.5 87.2 83.2 83.6 95.3 79.7 118.6 117.9 102.1 52.0 181.1 Cu 81.5 86.6 80.9 83.4 88.9 94.3 96.0 97.1 98.8 97.3 94.0 89.6 77.2 78.2 76.3 Zn 68.3 64.9 60.7 59.6 72.9 60.8 67.8 68.9 64.8 66.8 65.6 62.7 67.7 82.5 64.4 Ga 15.9 14.8 14 .7 13.5 15.5 13.4 15.0 15.3 14.7 14.8 14.5 14.8 14.4 16.9 14.6 Rb 0.46 0.40 0.39 0.09 0.31 0.30 0.25 0.26 0.24 0.23 0.32 0.18 0.49 0.69 0.51 Sr 128 116 121 89 102 82 90 93 89 89 78 84 95 117 158 Y 29.5 24.6 24.8 20.3 22.0 18.8 17.9 25.8 21.4 23.7 17.5 2 4.1 22.6 33.7 24.9 Zr 76.7 62.4 60.3 47.2 68.8 41.2 53.2 54.9 46.8 49.5 41.0 44.1 53.6 84.5 79.3 Nb 1.58 1.04 0.97 0.51 1.01 0.77 0.81 0.84 0.78 0.82 0.65 0.55 1.22 1.82 1.69 Ba 5.21 4.51 4.50 1.27 2.73 3.79 2.30 2.48 2.44 2.49 3.68 2.33 5.80 6.63 5.16 La 2.16 1.98 1.58 1.15 1.80 1.18 1.37 1.55 1.39 1.48 0.96 0.83 1.70 2.83 2.92 Ce 7.69 6.58 5.96 4.36 6.49 4.24 4.81 5.34 4.63 4.91 3.76 3.91 5.68 8.99 8.88 Pr 1.46 1.24 1.15 0.90 1.20 0.82 0.92 1.04 0.89 0.96 0.76 0.84 1.06 1.61 1.50 Nd 8.36 6.83 6.67 5.34 6.82 4.84 5.40 6.05 5.19 5.49 4.86 5.31 6.12 8.76 7.76 Sm 3.10 2.51 2.53 2.12 2.57 1.93 2.10 2.39 2.04 2.16 1.96 2.24 2.34 3.23 2.65 Eu 1.18 0.97 0.98 0.83 0.97 0.76 0.81 0.91 0.81 0.84 0.79 0.90 0.91 1.17 0.98 Gd 4.10 3.39 3.37 2.87 3.53 2.77 2.97 3.32 2.85 3.02 2.87 3.27 3.27 4.29 3.42 Tb 0.75 0.63 0.61 0.53 0.66 0.52 0.55 0.63 0.53 0.58 0.54 0.62 0.61 0.81 0.62 Dy 4.78 4.07 3.97 3.44 4.36 3.36 3.63 4.12 3.54 3.78 3.45 4.09 3.95 5.36 4.02 Ho 1.01 0.86 0.84 0.72 0.93 0.72 0.79 0.89 0.76 0.82 0.7 4 0.84 0.83 1.15 0.85 Er 2.88 2.47 2.43 2.04 2.65 2.08 2.26 2.53 2.20 2.36 2.13 2.39 2.40 3.28 2.47 Tm 0.43 0.36 0.36 0.30 0.39 0.31 0.33 0.38 0.33 0.34 0.31 0.36 0.36 0.49 0.37 Yb 2.74 2.29 2.32 1.90 2.48 1.96 2.07 2.43 2.09 2.24 2.00 2.21 2.29 3.23 2. 34 Lu 0.41 0.34 0.34 0.28 0.37 0.29 0.31 0.36 0.31 0.34 0.30 0.33 0.34 0.48 0.35 Hf 2.26 1.83 1.75 1.47 2.02 1.39 1.62 1.64 1.43 1.49 1.45 1.40 1.69 2.31 2.02 Ta 0.110 0.077 0.068 0.044 0.076 0.057 0.064 0.062 0.061 0.062 0.050 0.040 0.087 0.126 0.120 Pb 0.343 0.321 0.268 0.228 0.257 0.176 0.234 0.264 0.216 0.236 0.171 0.159 0.138 0.401 0.417 Th 0.085 0.060 0.069 0.030 0.019 0.048 0.028 0.047 0.041 0.043 0.042 0.039 0.067 0.110 0.106 U 0.037 0.025 0.021 0.014 0.028 0.018 0.024 0.024 0.018 0.019 0.019 0.015 0.029 0.041 0.043 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 146

146 Table D 1. Continued Sample 1571 1936 1572 1727 1572 1755 1561 1622 1562 2112 1564 1857 1564 2128 1564 2255 1565 1642 1565 1 724 1570 1626 1570 1949 F5 1a F7 4 F9 1 Isotopic ratios 208 Pb/ 204 Pb 37.352 37.362 37.375 37.348 37.328 37.319 37.416 37.785 2.20E 03 2.04E 03 2.38E 03 1.74E 03 3.77E 03 2.38E 03 1.77E 03 1.34E 03 207 Pb/ 204 Pb 15.440 15.436 15.440 15.437 15.441 15.437 15.443 15.493 8.59E 04 7.88E 04 9.93E 04 7.18E 04 1.43E 03 9.67E 04 6.14E 04 5.17E 04 206 Pb/ 204 Pb 17 .996 17.974 17.979 17.987 17.960 17.970 18.044 18.407 8.47E 04 8.12E 04 1.13E 03 8.00E 04 1.51E 03 1.12E 03 6.31E 04 6.29E 04 143 Nd/ 144 Nd 0.513216 0.513213 0.513228 0.513219 0.513251 0.513232 0.513201 0.513133 4.70E 06 5.00E 0 6 6.90E 06 6.80E 06 9.60E 06 7.10E 06 4.70E 06 8.90E 06 87 Sr/ 86 Sr 0.702358 0.702375 0.702336 0.702388 0.702300 0.702451 0.702387 0.702417 1.60E 05 8.80E 06 1.10E 05 1.40E 05 1.70E 05 1.50E 05 1.10E 05 2.60E 05 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 147

147 Table D 1. Continued Sample 1559 1647 1559 1751 1559 2058 1560 1522 1560 1651 1560 1843 1566 1611 1568 1714 1568 2014 1569 1901 Se amount MIB MIB MIB MIB MIB MIB MIB MIB MIB MIB Sc 32.5 33.1 38.7 34.3 39.0 36.1 42.1 37.5 42.1 43.1 V 187 199 244 207 234 216 259 240 248 266 Cr 276 266 362 269 345 276 361 364 356 241 Co 40.9 37.8 46.5 39.9 41.7 40.2 43.1 46.4 42.0 42.7 Ni 135.8 90.3 93.6 90.6 77.3 91.4 66.4 93.7 62.3 44.3 Cu 81.2 74.4 89.9 76.6 74.3 75.3 98.8 88.3 90.4 84.4 Zn 55.7 63.5 69.2 65.6 70.6 65.8 72.3 68.3 71.1 75.7 Ga 13.8 14.9 15.1 15.4 15.4 15.6 15.6 14.8 15.9 16.1 Rb 0.15 0.24 0.24 0.25 0.49 0.10 0.27 0.21 0.39 0.49 Sr 133 181 94 183 97 194 88 92 91 85 Y 22.1 24.0 25.9 26.7 25.9 28.7 26.5 22.3 26.7 27.9 Zr 63.3 92.7 57.9 93.1 55.9 98.4 61.0 56.5 57.4 55.3 Nb 0.56 0.54 0.77 0.56 1.01 0.43 0.88 0.75 0.89 1.11 Ba 1.70 2.64 2.18 2.73 4.77 1.09 2.62 2.02 4.17 4.99 L a 1.67 2.58 1.57 2.67 1.68 2.40 1.69 1.50 1.57 1.73 Ce 6.37 9.77 5.62 9.92 5.85 9.47 5.85 5.37 5.68 5.86 Pr 1.19 1.72 1.09 1.76 1.10 1.72 1.15 1.06 1.11 1.10 Nd 6.79 9.26 6.38 9.42 6.37 9.24 6.60 6.10 6.50 6.40 Sm 2.32 3.07 2.42 3.16 2.49 3.08 2.55 2.3 0 2.57 2.51 Eu 0.92 1.16 0.92 1.20 0.96 1.21 0.97 0.86 1.00 0.97 Gd 3.12 3.92 3.34 4.01 3.45 4.03 3.54 3.18 3.65 3.61 Tb 0.57 0.71 0.63 0.73 0.65 0.72 0.67 0.59 0.69 0.69 Dy 3.72 4.45 4.17 4.58 4.25 4.55 4.50 3.89 4.49 4.56 Ho 0.78 0.93 0.89 0.95 0.90 0.98 0.96 0.84 0.96 0.98 Er 2.30 2.63 2.58 2.72 2.62 2.74 2.76 2.41 2.78 2.85 Tm 0.34 0.39 0.39 0.40 0.39 0.40 0.41 0.35 0.42 0.44 Yb 2.19 2.50 2.48 2.58 2.53 2.59 2.64 2.32 2.72 2.80 Lu 0.33 0.37 0.37 0.38 0.38 0.38 0.40 0.35 0.40 0.43 Hf 1.63 2.49 1.69 2.48 1.77 2.43 1.82 1.66 1.85 1.79 Ta 0.048 0.057 0.059 0.057 0.075 0.049 0.068 0.058 0.068 0.082 Pb 0.282 0.274 0.271 0.463 0.172 0.451 0.257 0.244 0.132 1.762 Th 0.041 0.045 0.042 0.058 0.082 0.043 0.028 0.038 0.058 0.085 U 0.011 0.024 0.019 0.0 24 0.045 0.021 0.022 0.018 0.023 0.029 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 148

148 Table D 1. Continued Sample 1559 1647 1559 1751 1559 2058 1560 1522 1560 1651 1560 1843 1566 1611 1568 1714 1 568 2014 1569 1901 Isotopic ratios 208 Pb/ 204 Pb 37.358 37.383 37.334 37.334 37.257 1.70E 03 1.90E 03 1.69E 03 2.28E 03 3.60E 03 207 Pb/ 204 Pb 15.429 15.442 15.421 15.433 15.432 6.75E 04 7.38E 04 6.41E 04 9.72E 04 1.40E 03 206 Pb/ 204 Pb 17.940 18.016 17.933 17.983 17.884 8.02E 04 8.79E 04 7.08E 04 1.06E 03 1.59E 03 143 Nd/ 144 Nd 0.513239 0.513225 0.513216 0.513233 0.513248 8.80E 06 5.10E 06 4.90E 06 6.20E 06 5.70E 06 87 Sr/ 86 Sr 0.702228 0.702515 0.702336 0.702437 0.702275 2.50E 05 1.10E 05 1.20E 05 1.90E 05 1.20E 05 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 149

149 Table D 1. Continued Sample 1558 1657 1558 1722 1558 1839 1558 2014 F1 1 F3 4 F11 1 Seamount Sasha Sasha Sasha Sasha Sasha Sasha Sasha Sc 37.1 43.5 39.6 3 3.8 36.5 29.9 41.0 V 234 273 245 210 241 192 273 Cr 367 346 383 298 360 328 268 Co 44.3 46.1 46.8 44.0 38.7 42.8 39.8 Ni 61.2 41.0 65.4 131.9 94.2 153.6 79.1 Cu 98.9 99.6 102.5 80.9 76.5 82.8 68.5 Zn 67.1 76.3 69.9 64.3 63.9 59.2 75.8 Ga 15.0 15.7 1 4.8 15.2 14.7 13.9 16.4 Rb 0.21 0.27 0.23 0.19 0.40 0.16 1.12 Sr 77 76 72 165 108 79 124 Y 23.6 27.2 24.3 25.4 25.1 20.3 31.0 Zr 44.6 56.2 45.5 82.0 60.4 36.9 85.1 Nb 0.58 0.83 0.67 0.70 1.45 0.45 2.47 Ba 2.34 2.52 2.30 1.70 4.27 1.78 10.42 La 0.90 1.55 1.30 2.47 1.83 0.63 3.17 Ce 3.90 5.35 4.46 8.68 6.07 2.96 9.81 Pr 0.82 1.04 0.88 1.53 1.11 0.65 1.67 Nd 5.04 5.98 5.20 8.20 6.19 4.26 9.05 Sm 2.07 2.40 2.10 2.82 2.44 1.75 3.20 Eu 0.82 0.91 0.82 1.06 0.91 0.72 1.17 Gd 3.03 3.38 3.02 3.58 3.21 2. 53 4.27 Tb 0.57 0.66 0.59 0.66 0.60 0.48 0.80 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 150

150 Table D 1. Continued Sample 1558 1657 1558 1722 1558 1839 1558 2014 F1 1 F3 4 F11 1 Trace element s (ppm) Dy 3.82 4.37 3.89 4.20 3.89 3.15 5.17 Ho 0.82 0.95 0.85 0.87 0.85 0.68 1.09 Er 2.39 2.73 2.43 2.51 2.43 1.97 3.18 Tm 0.36 0.41 0.37 0.38 0.36 0.29 0.48 Yb 2.35 2.65 2.38 2.36 2.33 1.90 3.06 Lu 0.35 0.40 0.36 0.36 0.35 0.29 0.46 Hf 1.41 1.66 1.41 2.08 1.74 1.16 2.41 Ta 0.043 0.064 0.053 0.065 0.097 0.036 0.168 Pb 0.175 0.209 0.221 0.419 0.267 0.140 0.344 Th 0.040 0.038 0.036 0.029 0.081 0.032 0.169 U 0.010 0.016 0.014 0.017 0.030 0.006 0.058 Isotopic ratios 208 Pb/ 204 Pb 37.38 3 37.352 37.244 37.758 2.43E 03 1.02E 02 1.89E 03 7.00E 03 207 Pb/ 204 Pb 15.450 15.452 15.425 15.499 1.10E 03 2.96E 03 7.14E 04 2.20E 03 206 Pb/ 204 Pb 17.968 17.965 17.912 18.292 1.32E 03 2.39E 03 7.55E 04 2.20E 03 143 Nd/ 144 Nd 0.513242 0.513254 0.513212 0.513131 7.70E 06 5.40E 06 5.40E 06 5.30E 06 87 Sr/ 86 Sr 0.702345 0.702356 0.702218 0.703274 1.50E 05 2.00E 05 1.80E 05 4.40E 05 Notes: Trace element concentrations in ppm and analyzed by ICP MS; isotopic ratios analyzed by MC ICP MS

PAGE 151

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161 BIOGRAPHICAL SKETCH Nichelle Lynn Hann was born as Nichelle Lynn Baxter in 1984 in Redmond, Washington and grew up hearing about the famo us 1980 eruption of Mt. St. Helens. She is the middle child of three children, and, at the age of ten, she and her family moved to Atlanta, Georgia where her love for science and fascination with volcanoes continued to grow. After four years in the Deep So uth, the Baxter family moved to Orem, Utah, in the shadow of the Wasatch Mountains. Here, Nichelle completed her secondary education and fell in love with the great outdoors. A neighbor persuaded her to major in geology at Brigham Young University and she completed her undergraduate degree there in three years. She decided to continue her education at BYU and involved the study of volatiles in rocks from Stromboli volcano and ho w they are involved in the transport and formation of metal alloys. During her time at BYU, Nichelle was able to travel to many exciting places including most of the southwest and northeast portions of the US as well as Hawaii, Switzerland, and Italy. Afte r graduating with a Master of Science degree, Nichelle decided to return to the east coast and work on her PhD at the University of Florida starting in the fall of 2008. Here she researched the geochemistry of mid ocean ridge lavas and the results of her r esearch are detailed in this dissertation. In the fall of 2009, Nichelle met the love of her life Jared Hann, and she married him in May of 2011. In the summer of 2012, Nichelle completed her dissertation and she received her Doctor of Philosophy degree in August of 2012.