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Geochemistry of Cretaceous and Tertiary Plutons of the Great Falls Tectonic Zone

Permanent Link: http://ufdc.ufl.edu/UFE0020520/00001

Material Information

Title: Geochemistry of Cretaceous and Tertiary Plutons of the Great Falls Tectonic Zone Implications for Crustal Evolution
Physical Description: 1 online resource (50 p.)
Language: english
Creator: Probst, Kelly R
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: geochemistry, isotopes, montana, plutons
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Constraining the age of the crust and tectonic origin of the Great Falls tectonic zone (GFTZ) are important to understanding the accretionary history of Laurentia. Because the basement of the GFTZ is not well exposed, isotopic and elemental studies of the Cretaceous and Tertiary plutons intruded into this zone provide constraints on the age and composition of this crust. Trace elements, Sr, Nd, and Pb isotopic compositions of these magmatic rocks show several important characteristics: 1) LREE enrichment with minimal Eu anomalies and HREE contents < 10x chondrites indicate a mafic lower crustal source containing garnet, amphibole, and/or pyroxene with little or no plagioclase, 2) Depletion in HFSE (e.g., Nb) suggests this source was originally formed in a convergent margin, 3) Sm-Nd model ages (TDM) range from 1.1-1.9 Ga and whole rock Pb isotopes provide a nearly linear array at ~2.1 Ga, indicating that Archean crust is unlikely to be involved. Lu/Hf isotopic systematics preserved in zircon grains from individual plutons reveal Paleoproterozoic model ages in all cases. The western Highland Mountains contain an additional zircon population characterized by an Archean model age (~3.0 Ga); there is no evidence of Archean grains within the eastern study area. These observations support models that suggest the GFTZ formed as the result of a collision between the Medicine Hat Block and the Wyoming province in the Paleoproterozoic, but that the collision was not along two parallel margins. Instead, these data support the idea of an oblique convergence between the Medicine Hat and Wyoming Province that resulted in the formation of new Paleoproterozoic crust, the reworking of Archean crust, and the imbrication of Archean and Paleoproterozoic crust. Documentation of these relationships and the tectonic evolution of the GFTZ provide important criteria for identifying the conjugate margin of western Laurentia in Rodinia paleoreconstructions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Kelly R Probst.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Mueller, Paul A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0020520:00001

Permanent Link: http://ufdc.ufl.edu/UFE0020520/00001

Material Information

Title: Geochemistry of Cretaceous and Tertiary Plutons of the Great Falls Tectonic Zone Implications for Crustal Evolution
Physical Description: 1 online resource (50 p.)
Language: english
Creator: Probst, Kelly R
Publisher: University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2007

Subjects

Subjects / Keywords: geochemistry, isotopes, montana, plutons
Geological Sciences -- Dissertations, Academic -- UF
Genre: Geology thesis, M.S.
bibliography   ( marcgt )
theses   ( marcgt )
government publication (state, provincial, terriorial, dependent)   ( marcgt )
born-digital   ( sobekcm )
Electronic Thesis or Dissertation

Notes

Abstract: Constraining the age of the crust and tectonic origin of the Great Falls tectonic zone (GFTZ) are important to understanding the accretionary history of Laurentia. Because the basement of the GFTZ is not well exposed, isotopic and elemental studies of the Cretaceous and Tertiary plutons intruded into this zone provide constraints on the age and composition of this crust. Trace elements, Sr, Nd, and Pb isotopic compositions of these magmatic rocks show several important characteristics: 1) LREE enrichment with minimal Eu anomalies and HREE contents < 10x chondrites indicate a mafic lower crustal source containing garnet, amphibole, and/or pyroxene with little or no plagioclase, 2) Depletion in HFSE (e.g., Nb) suggests this source was originally formed in a convergent margin, 3) Sm-Nd model ages (TDM) range from 1.1-1.9 Ga and whole rock Pb isotopes provide a nearly linear array at ~2.1 Ga, indicating that Archean crust is unlikely to be involved. Lu/Hf isotopic systematics preserved in zircon grains from individual plutons reveal Paleoproterozoic model ages in all cases. The western Highland Mountains contain an additional zircon population characterized by an Archean model age (~3.0 Ga); there is no evidence of Archean grains within the eastern study area. These observations support models that suggest the GFTZ formed as the result of a collision between the Medicine Hat Block and the Wyoming province in the Paleoproterozoic, but that the collision was not along two parallel margins. Instead, these data support the idea of an oblique convergence between the Medicine Hat and Wyoming Province that resulted in the formation of new Paleoproterozoic crust, the reworking of Archean crust, and the imbrication of Archean and Paleoproterozoic crust. Documentation of these relationships and the tectonic evolution of the GFTZ provide important criteria for identifying the conjugate margin of western Laurentia in Rodinia paleoreconstructions.
General Note: In the series University of Florida Digital Collections.
General Note: Includes vita.
Bibliography: Includes bibliographical references.
Source of Description: Description based on online resource; title from PDF title page.
Source of Description: This bibliographic record is available under the Creative Commons CC0 public domain dedication. The University of Florida Libraries, as creator of this bibliographic record, has waived all rights to it worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law.
Statement of Responsibility: by Kelly R Probst.
Thesis: Thesis (M.S.)--University of Florida, 2007.
Local: Adviser: Mueller, Paul A.

Record Information

Source Institution: UFRGP
Rights Management: Applicable rights reserved.
Classification: lcc - LD1780 2007
System ID: UFE0020520:00001


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89d8a0e0431a077a266a80c335e91e11
00432fc899f6adecbe8ddf53caf31fd8aa7e99b5







GEOCHEMISTRY OF CRETACEOUS AND TERTIARY PLUTONS OF THE GREAT
FALLS TECTONIC ZONE: IMPLICATIONS FOR CRUSTAL EVOLUTION





















By

KELLY R. PROBST


A THESIS PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2007

































2007 Kelly R. Probst



























Dedicated to Norton and Higgins









ACKNOWLEDGMENTS

This research was funded by the Tobacco Root Geologic Society, the Colorado Scientific

Society, National Science Foundation (EAR 0106592), and the USGS (05HQGR0156). We

thank Jim Vogl, David Foster, David Mogk, and Josh Richards for their assistance in sample

collection, Sam Coyner for his guidance in sample preparation, Darryl Henry for CL and SEM

images of the zircon crystals, and to David Foster, Joe Meert, and Shawn Malone for their

insightful reviews.










TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ..............................................................................................................4

LIST OF TABLES ........... ... ...... ..................................................... 6

LIST OF FIGURES .................................. .. .... ... ...............7

ABSTRAC T ........................................................................ 8

CHAPTER

1 IN TR O D U CTION ............... .............................. ..................... ........ .. 10

B ack g rou n d ................... ...................1...................0..........
R regional Setting ................................................. 12

2 M E T H O D S .......................................................................................................1 5

S am p lin g S trateg y .............................................................................................................. 1 5
Geochem ical Preparation ............................................. 15
M mineral Separation ............................................. 16
Z ircon A nalysis.................................................... 17

3 R E S U L T S ..........................................................................2 2

M aj or E lem ents ............................................................................... 22
T ra c e E le m e n ts .................................................................................................................. 2 3
Iso to p e s ................... ...................2...................3..........
Z irc o n s .............. ...... .............................................................2 4

4 D IS C U S S IO N ........................................................................................................3 7

M ajo r E lem en ts .........................................................................................3 7
T ra c e E le m e n ts .................................................................................................................. 3 7
A g e of th e L ow er C ru st .................................................................................................3 9
T ectonics...................................................................... 4 1

5 C O N C L U SIO N S ................................................................44

L IST O F R E F E R E N C E S ....................................................................................................4 5

B IO G R A PH IC A L SK E T C H .................................................................................................... 50









LIST OF TABLES

Table page

2-1 Individual zircon analyses.............................................. ......................................... 18

3-1 W hole-rock elem mental data ........................................................................... 26

3-2 Sam ple descriptions ..................................... ... .. ......... ...... ....... 28

3-3 W hole rock isotopic data ......................................................................... ....................29









LIST OF FIGURES


Figure pe

1-1. Simplified geologic mapof the study area ...............................................14

2-1. CL image of "typical" zircon grains from the Highland Mountains (HM 02) ..................21

3-1. The classification of granitoids based on their molecular normative An-Ab-Or
com position ............................................. 30

3-2 T otal alk ali v s. SiO 2 .............................................................................. .......... .. .. ..3 1

3-3. Trace element abundance diagrams, normalized to N-MORB ......................................32

3-4. Rare earth element (REE) abundances normalized to chondritic meteorite values...........33

3-5. Initial 87Sr/86Sr and ENd variation diagram ............................................................ ...... 34

3-6. W hole rock Pb isotopic plot ........................................................................ 35

3-7. Individual zircons from the Crazy (CZ 03-05), the Highland (HM 02) and the
Beartooth Mountains (BT 03) were analyzed via La-ICP-MS......................................36









Abstract of Thesis Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Master of Science

GEOCHEMISTRY OF CRETACEOUS AND TERTIARY PLUTONS OF THE GREAT
FALLS TECTONIC ZONE: IMPLICATIONS FOR CRUSTAL EVOLUTION
By

Kelly R. Probst

August 2007

Chair: Paul Mueller
Major: Geology

Constraining the age of the crust and tectonic origin of the Great Falls tectonic zone

(GFTZ) are important to understanding the accretionary history of Laurentia. Because the

basement of the GFTZ is not well exposed, isotopic and elemental studies of the Cretaceous and

Tertiary plutons intruded into this zone provide constraints on the age and composition of this

crust. Trace element, Sr, Nd, and Pb isotopic compositions of these magmatic rocks show

several important characteristics: 1) LREE enrichment with minimal Eu anomalies and HREE

contents < 10x chondrites indicate a mafic lower crustal source containing garnet, amphibole,

and/or pyroxene with little or no plagioclase, 2) Depletion in HFSE (e.g., Nb) suggests this

source was originally formed in a convergent margin, 3) Sm-Nd model ages (TDM) range from

1.1-1.9 Ga and whole rock Pb isotopes provide a nearly linear array at -2.1 Ga, indicating that

Archean crust is unlikely to be involved. Lu/Hf isotopic systematics preserved in zircon grains

from individual plutons reveal Paleoproterozoic model ages in all cases. The western Highland

Mountains contain an additional zircon population characterized by an Archean model age (-3.0

Ga); there is no evidence of Archean grains within the eastern study area. These observations

support models that suggest the GFTZ formed as the result of a collision between the Medicine

Hat Block and the Wyoming province in the Paleoproterozoic, but that the collision was not









along two parallel margins. Instead, these data support the idea of an oblique convergence

between the Medicine Hat and Wyoming Province that resulted in the formation of new

Paleoproterozoic crust, the reworking of Archean crust, and the imbrication of Archean and

Paleoproterozoic crust. Documentation of these relationships and the tectonic evolution of the

GFTZ provide important criteria for identifying the conjugate margin of western Laurentia in

Rodinia paleoreconstructions.









CHAPTER 1
INTRODUCTION

Background

Many aspects of the evolution of Laurentia remain unclear because the locations of

boundaries between many basement age provinces are not well constrained. One outstanding

example of this problem is exemplified by the number of extant proposals for the identity of the

craton(s) that separated from SW Laurentia during the Neoproterozoic breakup of Rodinia.

Australia, South China, and Siberia have been proposed as this conjugate, but the paucity of high

resolution geologic and paleomagnetic data prevent the development of a unique solution

(Burrett and Berry, 2000; Karlstrom et al., 2001; Wingate et al., 2002; Gallet et al., 2000; Sears

and Price, 2003; Meert and Torsvik, 2003). One key area that is critical to reconstructing

Laurentia is the Precambrian basement of the Great Falls tectonic zone (GFTZ). This zone

remains poorly characterized because of the lack of basement exposure due to the accumulation

of a thick sedimentary cover (e.g., Belt-Purcell), Mesozoic terrane accretion, and plutonism

(O'Neil and Lopez, 1985; Mueller, et al., 1995; Boerner et al., 1998,). A potential window into

this largely buried basement is available via study of the numerous Mesozoic and Cenozoic

plutons within the GFTZ. Extensive plutonism marked the Mesozoic and Cenozoic of the

western United States, including the GFTZ, which was probably the result of Farallon Plate

subduction beneath the Cordilleran margin (Dickinson, 1981; Humphreys et al., 2003). The

composition of these mostly felsic plutons provides an indirect sample of the Precambrian

basement, as suggested by DePaolo, (1988). DePaolo (1988) showed that granitoid rocks can

provide a reliable means of sampling the isotopic composition of the deeper parts of the crust.

Identifying the petrogenetic processes involved in forming these plutons provides invaluable

information about source material and/or interactions with the intervening crust.









Systematic variations of trace element and isotopic systems provide highly sensitive tools

in correlating the chemistry of these young plutonic rocks to their petrogenetic processes and

sources within mantle and crustal reservoirs (e.g., Farmer and DePaolo, 1983; Zartman, 1988).

Early isotopic mapping in the western United States was conducted in the 1970's using 87Sr/86Sr

as the primary tool. Kistler and Peterman (1973) identified the proposed boundary between

cratonic North America and Phanerozoic accreted terranes by mapping Sr isotopic ratios of

young plutonic rocks and identified this boundary as the 87Sr/86Sr 0.706 line. They demonstrated

that the initial strontium isotopic ratios in young rocks located in central California were

dependent on geographic location, reflecting the distribution of basement rocks of differing ages

and compositions (Kistler and Peterman, 1973). This approach was expanded by Farmer and

DePaolo (1983), who used Sm-Nd systematics to propose that the interactions of mantle and

crust during the genesis of continental granitic magmas are influenced by their distance from the

continental margin. They conducted a comparative Nd and Sr isotopic study across the northern

half of the Great Basin of Nevada and Utah to the east of the Great Basin (e.g., spanning from

the continental margin to the cratonic interior). It was demonstrated that isotopic signatures of

plutons east of the Roberts Mountain Thrust (RMT) are predominantly influenced by the

Precambrian crystalline basement, whereas plutons west of the RMT are primarily derived from

mantle and/or young crustal sources (Farmer and DePaolo 1983). This observation led to their

identification of the western edge of the Precambrian basement as the RMT, 100-200 km east of

the 87Sr/86Sr 0.706 line of Kistler and Peterman (1973).

Bennet and DePaolo (1987) extended this approach and recognized that identifying the

boundary between different crustal age-provinces can provide information about the formation

and subsequent modification of the continents. Bennet and DePaolo (1987) used Sm-Nd









systematics to compare Nd age provinces to the isotopic Pb provinces of the southwestern United

States, previously identified by Zartman (1984). Although there are a total of four lead isotopic

provinces in the southwestern United States (Zartman, 1974), Nd isotopic mapping delineates

only three. In the Wyoming Province, one of the oldest elements of Laurentia, Wooden and

Mueller (1988) used a combination of Sr, Nd, and Pb systematics and trace element

compositions of late Archean igneous rocks of the Beartooth Mountains to postulate a

subduction origin for the voluminous late Archean crust of the northern Wyoming Province

along with contemporaneous metasomatism of the accompanying mantle wedge.

Regional Setting

Several workers have proposed that the Wyoming Province collided with the southern

edge of the Rae-Hearne craton and/or the intervening Medicine Hat block as part of a series of

orogenic events that led to the assembly of Laurentia's main components during the

Paleoproterozoic (e.g., O'Neil and Lopez, 1985; Hoffman, 1988; Mueller et al., 2005; Dahl et al.,

1999). This collision resulted in the formation of a suture zone, incorporating both juvenile crust

formed during convergence as well as reworked Archean crustal elements, and has been labeled

the Great Falls tectonic zone (GFTZ; O'Neil and Lopez, 1985; Mueller et al., 2002) (Figure 1-1).

The proportion of these disparate elements, however, is unclear. Juvenile Paleoproterozoic

crustal products are documented only in the Little Belt Mountains of southwestern Montana

(Mueller, et al., 2002). A contrasting interpretation of the GFTZ suggests that the belt of NE-SW

trending features of the GFTZ, including magnetotelluric patterns, end abruptly at the

intersection of the Trans-Hudson orogen in southwestern-most Saskatchewan, Canada. These

authors (Boerner et al., 1998) concluded that the GFTZ is an Archean structure that was later

reactivated as an intracratonic shear zone during the Paleoproterozoic.









In this study we use major and trace element, Sr, Nd, and Pb isotopic values of Cretaceous

and Tertiary magmatic rocks of intermediate composition (i.e, those likely derived from lower

crustal sources) and Lu-Hf systematics of zircons to gain insight into the age and nature of the

lower crust within the GFTZ and constrain the tectonic origin of the GFTZ. Although isotopic

mapping has been conducted on a large scale throughout western North America (Kistler and

Peterman, 1973; Farmer and DePaolo, 1983; Bennet and DePaolo, 1987), little work has been

done to define smaller scale boundaries within this region. The northwestern edge of the

Wyoming craton represents one area where detailed spatial resolution is required to assess the

role it played during the amalgamation of Laurentia and as a consequence, its importance for

testing models for the Rodinia configuration of Laurentia (e.g., Gunn, 1991, Mogk et al., 1992).

Using K-T plutons that have been intruded into the GFTZ as probes of the lower crust will

produce a high resolution image of lower crustal composition in this region and provide possibly

valuable constraints for both Proterozoic paleogeographic/paleotectonic reconstructions and for

testing proposed conjugate cratons in Rodinia reconstructions (e.g., AUSWUS (Burrett and

Berry, 2000; Karlstrom et al., 2001), AUSMEX (Wingate et al., 2002), SIBCOR (Gallet et al.,

2000; Sears and Price, 1978, 2000, 2003; Meert and Torsvik, 2003), SWEAT (Jefferson, 1978;

Moores, 1991; Hoffman, 1991; Ross et al., 1992)).






















Big Belt Mtns.
9


Little Belt Mtns.


as ts.

Castle Mtns.


Flint Creek
o
batholith

o
Pioneer
batholith


I WYOMING




Archean exposures
K-T magmatic rocks
~ 1.8 Ga basement
Sample(s) Collected O


Figure 1-1. Simplified geologic map modified from Mueller, et al., (2005) of the study area with
generalized sample locations. The inset shows the study area (dotted box) in relation
to the 0.706 Sr line (dashed line) of Kistler and Peterman (1973).


BBb

I
i. -,
P.









CHAPTER 2
METHODS

Sampling Strategy

Sampling of Phanerozoic plutons was conducted in two areas of known or suspected

Proterozoic crust (Figure 1-1). An eastern group was collected from units near the

Paleoproterozoic crust in the Little Belt Mountains and within the general confines of the

Montana alkali province (MAP). This group contains three samples from the Castle Mountains,

three samples from the Crazy Mountains, two samples from the Little Belt Mountains, and one

sample from the Big Belt Range. The western group comes from an area of suspected mixed

Archean and Proterozoic crust in the western GFTZ (e.g., Mueller et al., 1996; Foster et al.,

2006). Samples were collected in the Flint Creek Range, the Highland Mountains, and the

Pioneer Mountains. Due to the exposure of well documented Archean lithologies within the

Beartooth Mountains, a sample, (BT 03), was collected to provide an Archean reference and to

add Hf isotopic data to the Beartooth geochemical database.

Geochemical Preparation

Rock samples were crushed using a steel jaw crusher and then ground using a tungsten

carbide ball mill to generate homogeneous fine powders for geochemical analysis. Whole rock

major element data were obtained via XRF analysis (at the Northern Ontario Division of Mines).

All other geochemical analyses were conducted at the University of Florida. Trace element data

were collected after the whole rock powders were dissolved using a HF-HNO3 mixture and

analyzed using the Element-2 ICP-MS calibrated using the following standards: ENDV, QLO-1,

BCR-2, AGV-1, RGM-1, and G-2. Sm-Nd, Rb-Sr, and Pb were separated from whole rock

samples using standard column chemistry methods (e.g., Heatherington et al., 1991). Rb-Sr and

Sm-Nd spikes were added prior to dissolution in order to determine the elemental concentrations.









Rb-Sr, Sm-Nd, and Pb isotopic compositions were measured on a "Nu-Plasma" MC-ICP-MS.

Isotopic Sr ratios were acquired in static mode using 5 Faraday collectors and 87Sr/86Sr was

corrected for mass-bias using the exponential law and 86Sr/"Sr=0.1194. All analyses were done

using on-peak measured zeros in order to correct for isobaric interference from the presence of

impurities of Kr in the Ar gas. The data are reported relative to a NBS 987 value of

87Sr/86Sr=0.71025 (+/-0.00003, 20), which is applicable to all samples. Nd isotopic

measurements were conducted in static mode acquiring simultaneously 142Nd on low-2, 143Nd on

low-1, 144Nd on Axial, 145Nd on high-1, 146Nd on high-2, 147Sm on high-3, 148Nd on high-4, and

150Nd on high-5 Faraday detectors. The measured 144Nd, 148Nd, and 150Nd beams were corrected

for isobaric interference from Sm using 147Sm/144Sm = 4.88, 147Sm/148Sm = 1.33, and

147Sm/10Sm = 2.03. All measured ratios were normalized to 146Nd/144Nd = 0.7219 using an

exponential law for mass-bias correction. The data are reported relative to a JNdi-1 value of

143Nd/144Nd=0.512099 (+/-0.000018, 20), which is applicable to all samples. Pb isotopic

analyses were also conducted on the Nu-Plasma MC-ICP-MS using the Tl normalization

technique (Kamenov et al., 2004). The Pb isotopic compositions are reported relative to the

following NBS 981 values: 206Pb/204Pb=16.937 (+/-0.004, 20), 207Pb/204Pb=15.491 (+/-0.004,

20), 208Pb/204Pb=36.695 (+/-0.009, 20), and are applicable to all samples.

Mineral Separation

Samples were pulverized in a jaw crusher and ground in a disc mill to ensure the

disaggregation of rock fragments. The pulverized material was then sieved to separate the

fraction greater than 250 rm. The <250rm material was then passed across the Gemini water

table to generate a heavy mineral separate. Heavy mineral separates were then processed using

tetrabromoethane (TBE) and methylene iodine (MI). The density separates received further

treatment via magnetic separation on a Frantz isodynamic mineral separator at 1 A electrical









current with progressive reduction of inclination from +6 degrees down to +1 degree, depending

on the individual sample. The separates were then hand picked to isolate representative zircon

grains (Figure 2-1). The zircon grains were mounted in epoxy plugs to facilitate LA-ICP-MS

analysis. A zircon standard, FC-1 separated from the Duluth gabbro was also mounted together

with the sample zircons (Mueller et al., 2007).

Zircon Analysis

Zircon grains mounted in epoxy plugs were analyzed via laser ablation (LA) (Merchantek

UP-213 with Supercell) connected to the "Nu-Plasma" MC-ICP-MS. Prior to ablation, the

grains were subjected to cathode luminescence imaging by D. Henry at Louisiana State

University to identify any zonation or other heterogeneities. The plugs were then inserted into

the laser ablation chamber and viewed using an internal video camera system. Ablation

proceeded in a pattern, ablating the standard FC-1, several sample grains, then the standard

again. For both standards and samples, ion beams were simultaneously collected for Lu, Hf, and

Yb following methods in Mueller et al. (2007). The reported Hf isotope data are relative to the

following values of the FC-1 standard: 176Hf/177Hf=0.282168 (+/-0.000026, 2C n=155), and is

applicable to all samples. In order to verify the LA protocol one of the zircon samples were

dissolved in HF-HNO3 using Teflon-lined bombs under high-pressure and temperature and Hf

was separated from the REE elements following a method described in Coyner et al. (2004). Hf

isotopes were also measured on the "Nu-Plasma" MC-ICP-MS via wet plasma to confirm results

from the LA method (Table 2-1).










Table 2-1. Individual zircon analyses


Sample


CZ03-01
CZ03-04
CZ03-08
CZ03-05
CZ03-14
CZ03-16
CZ03-18
CZ03-23
CZ03-25
CZ03-27
CZ03-37
CZ03-70
Mean
Min
Max


176Lu/177Hf 176Hf/177Hf cor.
Crazy Mtns.


0.00111507
0.00121782
0.00094786
0.00114934
0.00095221
0.00059549
0.00099166
0.00103352
0.00093085
0.00071784
0.00126385
0.00111009
0.00100213
0.00059549
0.00126385


CZ04-74
CZ04-71
CZ04-69
CZ04-60
CZ04-61
CZ04-59
CZ04-56
CZ04-57
CZ04-57
CZ04-54
CZ04-54
CZ04-50
CZ04-45
CZ04-41
CZ04-38
CZ04-31
CZ04-12
CZ04-02
CZ04-01
Mean
Min
Max
Multiple Zircons
Dissolved
CZ04 (Disolved grains)
CZ04 (Disolved
grains)
CZ04 (Disolved
grains)
Mean


0.00307948
0.00228082
0.00261500
0.00347784
0.00161267
0.00277820
0.00116242
0.00184098
0.00184098
0.00170567
0.00321592
0.00267167
0.00303747
0.00308721
0.00212818
0.00069923
0.00188463
0.00235211
0.00151271
0.00226610
0.00069923
0.00347784


0.282314
0.282366
0.282312
0.282290
0.282314
0.282332
0.282313
0.282295
0.282311
0.282279
0.282335
0.282388
0.282321
0.282279
0.282388
Crazy Mtns.
0.282328
0.282383
0.282362
0.282215
0.282379
0.282316
0.282296
0.282335
0.282335
0.282327
0.282374
0.282351
0.282304
0.282270
0.282285
0.282307
0.282305
0.282328
0.282347
0.282320
0.282215
0.282383


0.00000218


0.00000354


0.282345


-16.20
-14.36
-16.27
-17.05
-16.20
-15.56
-16.23
-16.87
-16.30
-17.43
-15.45
-13.58
-15.96
-17.43
-13.58


-15.70
-13.76
-14.50
-19.70
-13.90
-16.13
-16.83
-15.45
-15.45
-15.74
-14.07
-14.89
-16.55
-17.75
-17.22
-16.44
-16.52
-15.70
-15.03
-15.98
-19.70
-13.76


0.282332

-15.10


eHfinitial


-15.14
-13.31
-15.21
-15.99
-15.14
-14.49
-15.17
-15.81
-15.24
-16.36
-14.40
-12.52
-14.90
-16.36
-12.52


-14.71
-12.74
-13.49
-18.72
-12.86
-15.12
-15.78
-14.42
-14.42
-14.70
-13.09
-13.88
-15.56
-16.76
-16.20
-15.37
-15.48
-14.68
-13.98
-14.96
-18.72
-12.74


-15.56

-14.47


T(DM)


1.30
1.23
1.30
1.33
1.29
1.26
1.30
1.32
1.30
1.33
1.28
1.20
1.29
1.20
1.33


1.35
1.24
1.28
1.53
1.22
1.36
1.33
1.30
1.30
1.30
1.29
1.30
1.38
1.44
1.38
1.30
1.34
1.32
1.27
1.33
1.22
1.53


-14.01

1.22


0.00000376 0.282345 -15.10 -14.01 1.22
0.00000365 0.282345 -15.10 -14.16 1.22










Table 2-1. Continued.


Sample


CZ05-01
CZ05-02
CZ05-07
CZ05-10
CZ05-11
CZ05-18
CZ05-22
CZ05-21
CZ05-26
CZ05-28
CZ05-30
CZ05-31
CZ05-35
CZ05-36
CZ05-37
CZ05-42
CZ05-44
CZ05-45
CZ05-51
CZ05-57
Mean
Min
Max
Sample


HM02-01A
HM02-01B
HM02-04
HM02-09
HM02-12
HM02-12B
HM02-17
HM02-21
HM02-22
HM02-23
HM02-28
HM02-28
HM02-29
HM02-30
HM02-60
HM02-36
HM02-39


176Lu/177Hf 176Hf/177Hfcor.
Crazy Mtns.
0.00049381 0.282298
0.00031701 0.282286
0.00265842 0.282371


0.00043758
0.00106780
0.00037842
0.00148518
0.00174578
0.00042284
0.00107653
0.00046464
0.00124491
0.00059057
0.00097469
0.00095135
0.00051158
0.00120777
0.00042337
0.00058866
0.00123275
0.00091368
0.00031701
0.00265842
176Lu/177Hf


0.00247796
0.00087344
0.00052546
0.00061265
0.00061081
0.00057584
0.00065839
0.00078408
0.00064186
0.00103095
0.00203401
0.00203401
0.00030520
0.00080678
0.00136552
0.00112133
0.00067533


0.282315
0.282287
0.282234
0.282254
0.282255
0.282296
0.282293
0.282287
0.282249
0.282293
0.282284
0.282290
0.282365
0.282285
0.282303
0.282309
0.282334
0.282294
0.282234
0.282371
176Hf/177Hf cor.
Highland Mtns.
0.281815
0.281141
0.281223
0.281203
0.281932
0.281996
0.281788
0.281163
0.281878
0.281148
0.281835
0.281835
0.281145
0.281899
0.281863
0.281799
0.281994


eHf


-16.76
-17.19
-14.18
-16.16
-17.15
-19.03
-18.32
-18.28
-16.83
-16.94
-17.15
-18.50
-16.94
-17.26
-17.05
-14.39
-17.22
-16.59
-16.37
-15.49
-16.89
-19.03
-14.18
eHf


-33.84
-57.68
-54.78
-55.49
-29.71
-27.44
-34.80
-56.90
-31.62
-57.43
-33.14
-33.14
-57.54
-30.87
-32.15
-34.41
-27.51


TmDMi


-15.68
-16.10
-13.17
-15.08
-16.09
-17.94
-17.27
-17.25
-15.75
-15.88
-16.07
-17.44
-15.86
-16.20
-15.98
-13.32
-16.17
-15.50
-15.30
-14.01
-15.80
-17.94
-13.17
eHfinitial


1.30
1.31
1.27
1.28
1.34
1.39
1.40
1.41
1.30
1.33
1.32
1.40
1.31
1.34
1.33
1.21
1.34
1.29
1.29
1.28
1.32
1.21
1.41
TIDMm


-32.43
-56.19
-53.28
-53.99
-28.20
-25.94
-33.30
-55.41
-30.11
-55.95
-31.70
-31.70
-56.02
-29.38
-30.68
-32.93
-26.01


2.07
2.90
2.77
2.80
1.81
1.72
2.01
2.87
1.88
2.90
2.02
2.02
2.85
1.86
1.94
2.02
1.73


__ _


"""~


I










Table 2-1. Continued.


Sample
HM02-44
HM02-54
HM02-40
HM02-42
HM02-48
HM02-53
HM02-05
HM02-08
HM02-13
HM02-14
HM02-16
HM02-24
HM02-03
HM02-34
Mean
min
Max


BT03-01
BT03-08
BT03-13
BT03-17
BT03-19
BT03-21
BT03-26
BT03-29
BT03-30
BT03-32
BT03-30
BT03-34
BT03-42
BT03-52A
BT03-53
Mean
Min
Max


176Lu/177Hf
0.00082564
0.00081770
0.00124004
0.00080258
0.00122224
0.00088252
0.00106174
0.00103851
0.00074850
0.00071329
0.00115552
0.00074165
0.00073105
0.00079599
0.00096486
0.00030520
0.00247796

0.00101299
0.00025065
0.00146777
0.00049562
0.00075066
0.00099006
0.00031389
0.00024486
0.00070911
0.00045113
0.00053484
0.00083451
0.00040308
0.00143219
0.00116798
0.00073729
0.00024486
0.00146777


176Hf/177Hf cor.
0.281857
0.282328
0.281913
0.281956
0.281925
0.281837
0.281951
0.281987
0.281998
0.281942
0.281252
0.281918
0.281952
0.281897
0.281754
0.281141
0.282328
Beartooth Mtns.
0.280953
0.280888
0.280916
0.280934
0.280912
0.280968
0.280920
0.280919
0.280902
0.280948
0.280942
0.280906
0.280912
0.280957
0.280926
0.280927
0.280888
0.280968


eHf
-32.36
-15.70
-30.38
-28.86
-29.95
-33.07
-29.03
-27.76
-27.37
-29.35
-53.75
-30.20
-29.00
-30.94
-36.01
-57.68
-15.70

-64.33
-66.63
-65.64
-65.00
-65.78
-63.80
-65.49
-65.53
-66.13
-64.50
-64.72
-65.99
-65.78
-64.19
-65.28
-65.25
-66.63
-63.80


eHfinitial
-30.87
-14.21
-28.90
-27.36
-28.48
-31.58
-27.55
-26.28
-25.88
-27.85
-52.28
-28.70
-27.50
-29.45
-34.52
-56.19
-14.21


T(DM)
1.92
1.27
1.87
1.78
1.85
1.95
1.80
1.75
1.72
1.80
2.77
1.83
1.79
1.87
2.07
1.27
2.90

3.17
3.19
3.26
3.15
3.20
3.14
3.15
3.15
3.21
3.13
3.14
3.22
3.17
3.20
3.22
3.18
3.13
3.26


-63.06
-65.33
-64.39
-63.71
-64.50
-62.32
-63.98
-64.02
-64.64
-63.00
-63.22
-64.50
-64.27
-62.73
-63.81
-63.83
-65.33
-62.32
















































Figure 2-1. CL image of "typical" zircon grains from the Highland Mountains (HM 02) showing
igneous zoning.














21









CHAPTER 3
RESULTS

Major Elements

Major element data (Table 3-1) show that samples have SiO2 weight percent contents

between 55 and 73. Based on normative mineralogy this sample set includes monzogabbro to

syenite (Figures 3-1, 3-2). Estimated modal mineralogy and petrographic analysis, however,

suggest the samples are more accurately described as granite to monzogranite. The modes were

not determined quantitatively through point count analysis. The samples are best classified as

granitoids, with the exception of sample CZ 05 from the Crazy Mountains. This sample contains

no quartz and is best described as an amphibole-plagioclase cumulate (Table 3-2). Due to its

anomalous major elemental chemistry, it will be excluded from any further discussion of major

and trace elements. It is also important to note that sample BT03, from the Beartooth Mountains,

is an Archean basement sample, not a Mesozoic plutonic sample. The Flint Creek pluton,

(samples FC 01 and FC 02), is more specifically described and mapped as granodiorite by Lewis,

(1998). The samples collected from the Highland Mountains are from units described and

mapped by Ruppel et al., (1993). Highland Mountain sample HM01 is described as a

monzogranite and HM02 is described as a granodiorite. The extent of alteration (Table 3-2) is

determined based on a qualitative assessment, primarily on the extent of seritization of

plagioclase.

With the exception of BT 03, and two samples from the Crazy Mountains (CZ 03 and CZ

05), the eastern locations are more enriched in total alkalis (Na20+K20), ranging from 8 to 10%,

than their western, more calc-alkaline counterparts, that range from 6 to 8% (Figure 3-2). This

overall trend correlates well with published data, (i.e., the eastern group lies largely within the

Montana alkali province (MAP) and the western group lies within the slightly older, calc-









alkaline magmatic province of the Cordilleran orogenic belt. It is worth noting that the A1203

contents are low enough that muscovite is not present in any of the sample set. This implies that

the samples are likely to be classified as I-type granitoids (Chappell and White, 1974).

Trace Elements

Trace element data are presented in Table 1 and plotted normalized to the composition of

N-MORB using values of Sun and McDonough (1989) (Figure 3-3). The normalized data show

clear depletion in high field strength elements (HFSE) such as Nb, Zr, and Hf, a positive

anomaly in Pb concentrations, and no obvious Eu anomalies. All samples have LREE-enriched

rare earth patterns exceeding 100x chondrites (Figure 3-4). None of the samples show strong

depletions in HREE (<10x chondrites) that would be expected for melts equilibrated with garnet.

(La/Yb)N ratios are enriched in the east, with samples ranging from 13.45 to 66.68 with an

average of 32.45 whereas the western samples have a much more restricted range of 7.75 to

14.71 with a mean of 12.25, suggesting a more homogeneous source and/or set of petrogenetic

processes. Overall, the eastern samples are more enriched in the highly incompatible elements

such as Ce, Pb, Y, and Nb. For example, there is a geographic contrast in Y+Nb contents, with

the easternmost samples ranging from 18 to 100, with an average of 57 and the western samples

have much lower, more limited range of concentrations ranging from 29 to 39 with an average of

35, which reflects the general compositional contrasts between the more alkaline MAP suites and

the more calc-alkaline rocks of the western group.

Isotopes

The Sr, Nd, and Pb isotopic data are presented in Table 3-3. The amphibole-plagioclase

cumulate (CZ 05) is included in the isotopic discussion due to its isotopic similarity to the

granitoids, i.e., its cumulate nature only affects its elemental composition. The initial values

were calculated using an average age estimate of 70 Ma for the western samples and 50 Ma for









the eastern, MAP samples (Dudas et al., 1987; Harlan et al., 1988). The range of calculated

initial 87Sr/86Sr is 0.7053 to 0.7101, with an average of 0.7068. The range of initial strontium

isotopic compositions is greater in the western portion of the study area (0.7056 to 0.7101)

compared to the eastern study area (0.7053 to 0.7077). The difference is likely due to, the

presence of Archean crust in the western area.

Present day 144Nd/143Nd ratios range from 0.511381 to 0.5121219, and correspond to ENd

values of-24.52 to -8.17 and TDM (depleted mantle model age) of 1.97 to 1.1 Ga respectively.

The western portion of the study area typically has more restricted ENd values ranging from -

18.2 to -15.0 and TDM of 1.94 to 1.5 Ga compared to the wide range of -24.5 to -8.2 and TDM

ages of 1.97 to 1.1 Ga observed in the eastern group. On the 87Sr/86Sr and ENd correlation

diagram shown in Figure 3-5, the data plot in the lower right quadrant. The Archean basement

sample from the Beartooth Mountains, calculated for 50 Ma, is provided for reference.

Whole rock Pb isotopic compositions show a range of values, i.e., 206Pb/204Pb varies from

15.68 to 18.82, 207Pb/204Pb from 15.22 to 15.63, and 208Pb/204Pb from 36.44 to 38.86. These data

form a well correlated linear array on a 207Pb/204Pb vs. 206Pb/204Pb diagram that corresponds to an

age of 2082 160 Ma calculated with Isoplot (Ludwig, 2003) (Figure 3-6). This array includes

samples from both geographic and geochemical groups and, in particular, samples that contain

Pb elemental abundances ranging from 11.9 to 111.9 ppm (Table 2-1).

Zircons

Hafnium isotopic compositions of individual zircon grains are presented in Table 3-3. At

least twenty grains from selected samples were analyzed and their model ages (TDM) are

summarized in Figure 9. The mean 176Hf/177Hf ratio of 20 grains from CZ 04 is 0.282320 (+/-

0.000080, 2c), which corresponds to an epsilon Hf value of -16.0 and a TDM of 1.3 Ga. The

mean 176/177Hf ratio for three analyses of the dissolved grains from this sample is 0.282345 (+/-









0.000015, 20), which corresponds to an epsilon Hf value of -15.3 and a TDM of 1.2 Ga (Table 2-

1). The similarity of the Hf and TDM values suggests that both methods produced consistent

results. The advantage of using the in-situ laser ablation technique is that it allows for numerous

grains to be assessed individually, providing multiple model ages for a single whole rock sample,

thereby yielding better resolution of magmatic and source heterogeneity compared to a single

whole-rock measurement. Laser ablation analyses of zircon were conducted on five samples:

HM 02 from the Highland Mountains in the western portion of the study area, CZ 03, 04, 05

from the Crazy Mountains in the eastern portion of the study area, and BT03 from the Beartooth

Mountains, the known Archean basement sample. The following summarizes the average EHf

for the Crazy Mountains sites analyzed: -16.0 (CZ03), -16.0 (CZ04), and -16.9 (CZ05) with

ranges from -17.4 to -13.6 (CZ03), -19.7 to -13.8 (CZ04), and -19.0 to -14.2 (CZ05). The

Highland Mountains reveal more variability, with an average EHf of -36.0 and a range from -57.7

to -15.7. This wide range includes two distinct model age populations: -1.9 Ga and -2.8 Ga,

suggestive of a degree of Archean magmatic inheritance in this sample (Figure 3-7). The

Archean basement sample (BT 03) yielded an average EHf of -65.3, with values falling between -

66.6 to -63.8. These values are clearly far more negative than the values observe in the plutonic

zircons












Table 3-1. Whole-rock elemental data
Major Elements weight percent
(XRF)
BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 CA03 BT03 HM01 HM02 PM01 FC01 FC02
SiO2 68.09 69.16 62.44 56.14 58.94 47.02 73.75 67.54 66.56 58.86 67.11 70.02 63.81 62.29 55.26
A1203 17.10 14.68 16.25 15.00 17.27 17.02 13.58 15.21 15.12 16.18 15.98 15.18 16.75 16.45 15.74
Fe203 T 2.26 2.39 4.98 7.74 7.03 12.03 1.67 2.56 3.47 6.46 4.08 2.74 4.85 6.32 8.42
MgO 0.46 0.82 1.88 6.42 2.46 6.67 0.35 1.28 1.96 4.22 1.65 1.08 2.18 2.56 3.98
CaO 2.17 1.43 3.34 6.78 4.24 9.57 0.80 1.89 2.84 6.40 3.60 2.94 4.36 4.82 5.84
Na20 5.85 4.25 4.49 3.46 4.92 3.19 3.78 5.14 4.42 3.62 3.22 3.49 3.47 3.26 3.42
K20 3.59 4.38 4.96 2.18 3.31 1.14 4.79 3.42 3.78 2.28 4.42 4.04 3.11 3.04 3.20
TiO2 -- 0.05 0.56 1.02 0.99 2.48 0.20 0.04 0.26 0.36 0.33 0.12 0.40 0.48 0.87
MnO 0.06 0.06 0.10 0.11 0.10 0.10 0.03 0.02 0.04 0.11 0.08 0.06 0.08 0.09 0.13
P205 0.08 0.19 0.51 0.29 0.44 1.02 0.06 0.16 0.24 0.27 0.20 0.12 0.17 0.24 0.62
LOI 0.29 1.64 0.54 0.64 0.27 0.52 1.43 2.61 1.18 0.91 0.44 0.50 0.67 0.72 1.95
TOTAL 99.92 99.05 100.04 99.80 99.98 100.75 100.43 99.88 99.89 99.68 101.10 100.32 99.85 100.27 99.44

Trace Elements ppm (Element 2- ICP-MS)
BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 CA03 BT03 HM01 HM02 PM01 FC01 FC02
P 881.40 1755.39 4161.43 2613.96 3722.66 8848.78 816.36 1357.63 2121.94 2418.86 1817.13 1256.15 1587.27 2042.50 6319.86
SC 3.34 3.44 7.58 18.89 9.10 30.78 5.14 5.18 7.29 15.74 9.11 5.90 10.27 12.45 21.20
V 51.71 31.70 79.79 139.33 93.93 322.26 15.13 34.01 56.91 97.92 75.22 38.88 79.97 107.91 297.94
Cr 5.10 10.51 17.57 316.90 12.65 117.26 4.45 31.85 59.63 138.57 10.58 17.20 25.86 13.62 74.21
Mn 598.84 547.99 982.47 1074.24 979.98 981.06 380.70 180.91 434.73 1116.56 702.04 618.83 757.15 904.61 1481.08
Co 22.57 25.86 27.15 35.99 24.10 37.32 96.35 18.90 24.24 32.15 21.03 31.66 23.74 24.46 24.99
Ni 3.83 6.37 10.87 105.09 11.14 96.51 6.71 19.68 28.93 60.93 7.44 10.02 9.54 6.20 46.12
Cu 6.32 4.57 16.88 16.23 17.52 50.17 5.64 14.99 25.36 23.00 7.51 26.70 8.58 6.42 148.92
Zn 38.24 106.24 99.34 76.58 73.50 77.09 79.74 106.10 118.82 72.70 38.68 61.90 70.01 46.80 99.91
Ga 21.37 17.93 20.04 17.83 20.22 22.96 22.60 17.18 19.21 17.07 15.77 14.42 19.07 18.44 22.52
Rb 137.70 154.98 181.02 53.47 66.73 20.02 732.45 53.01 95.66 63.85 116.95 174.52 99.97 91.25 92.43
Sr 1278.26 838.51 901.50 867.21 895.30 1549.85 189.38 579.96 668.98 513.41 531.85 595.48 457.12 576.12 872.96














Table 3-1. Continued.
BB01 LB01 LB02 CZ03
Y 15.29 14.32 20.78 21.95
Zr 84.12 144.86 106.47 97.67
Nb 22.80 61.26 79.90 22.27
Ba 1692.40 1952.73 2273.60 1116.41
La 34.15 77.97 90.53 44.57
Ce 51.60 134.25 161.62 83.18
Pr 5.07 11.62 15.32 8.66
Nd 18.99 39.26 54.13 33.13
Sm 3.34 5.21 7.72 5.72
Eu 1.05 1.33 1.98 1.60
Gd 3.08 4.40 7.09 5.10
Tb 0.43 0.51 0.78 0.70
Dy 2.36 2.36 3.47 3.61
HO 0.47 0.42 0.64 0.69
Er 1.19 0.99 1.83 1.87
Tm 0.23 0.21 0.29 0.31
Yb 1.32 0.96 1.54 1.72
Lu 0.21 0.15 0.23 0.27
Hf 2.34 3.82 3.09 2.91
Ta 3.61 4.93 6.26 2.19
Pb 22.24 119.02 48.44 17.23
Th 9.24 51.17 32.20 9.52
U 2.99 6.88 4.65 2.08
La/Lu 164.46 524.81 388.51 167.75
La/Yb 1.10 2.52 2.92 1.44


CZ04
21.79
148.35
38.55
1761.62
53.78
96.21
9.59
35.86
6.00
1.76
5.41
0.73
3.56
0.64
1.57
0.31
1.41
0.23
3.99
3.84
17.25
11.09
2.31
237.61
1.73


CZ05
24.43
70.87
17.51
783.55
37.47
77.63
9.55
43.01
8.21
2.41
7.02
0.96
4.84
0.91
2.19
0.32
1.72
0.24
2.15
1.60
11.92
4.41
0.98
156.13
1.21


CA01
34.50
137.17
62.89
597.88
107.87
129.04
14.15
45.42
7.15
1.07
6.24
0.92
5.04
1.04
2.99
0.48
3.35
0.51
4.99
18.42
45.23
49.31
3.93
210.65
3.48


CA02 CA03
10.89 14.51
109.45 181.89
7.53 20.46
2005.46 2363.99
32.46 67.93
44.99 107.62
5.66 10.12
21.04 34.96
3.31 4.89
0.99 1.42
2.72 4.76
0.36 0.53
1.59 2.22
0.26 0.36
0.61 0.93
0.17 0.21
0.58 0.73
0.10 0.13
3.17 4.78
2.68 2.66
22.93 25.91
7.55 17.97
2.29 2.74
309.73 521.20
1.05 2.19


BT03 HM01 HM02 PMO1 FC01
21.39 23.85 20.99 21.47 21.41
126.38 72.75 83.65 64.30 51.47
7.64 15.09 16.97 11.98 10.95
1279.19 1036.84 1214.83 1297.30 1258.18
35.40 35.96 36.28 33.36 32.87
74.21 67.81 64.33 61.43 63.89
8.91 7.31 6.78 6.55 7.07
35.96 27.61 25.48 25.25 28.12
6.21 4.97 4.51 4.64 5.07
1.65 1.17 1.12 1.22 1.37
5.22 4.51 4.15 4.27 4.61
0.67 0.65 0.60 0.61 0.62
3.43 3.56 3.36 3.29 3.29
0.66 0.72 0.69 0.65 0.64
1.84 2.03 1.84 1.74 1.74
0.30 0.36 0.34 0.31 0.30
1.73 2.21 2.10 1.78 1.75
0.27 0.33 0.34 0.26 0.27
3.48 2.28 2.63 1.79 1.60
1.72 2.99 4.18 2.66 2.08
17.60 16.88 18.76 15.43 8.94
14.95 17.94 19.96 10.14 8.83
1.94 2.57 2.22 2.29 2.63
133.33 108.75 107.84 126.99 120.78
1.14 1.16 1.17 1.08 1.06


FC02
29.09
129.10
8.27
1033.94
29.12
56.80
6.49
27.15
5.48
1.65
5.30
0.78
4.55
0.96
2.65
0.42
2.70
0.41
3.46
0.85
14.66
6.38
1.30
71.67
0.94














Table 3-2. Sample descriptions


Sample
BB01
LB01
LB02
CZ03
CZ04
CZ05
CA01
CA02
CA03
BT03
HM01
HM02
PM01
FC01
k) FC02
00 Sample
BB01
LB01
LB02
CZ03
CZ04
CZ05
CA01
CA02
CA03
BT03
HM01
HM02
PM01
FC01
FC02


Mountain Range
Big Belt Mts
Little Belt Mts.
Little Belt Mts.
Crazy Mts.
Crazy Mts.
Crazy Mts.
Castle Mts.
Castle Mts.
Castle Mts.
Beartooth Mts
Highland Mts.
Highland Mts.
Pioneer Mts.
Flint Creek Mts.
Flint Creek Mts.
Mountain Range
Big Belt Mts
Little Belt Mts.
Little Belt Mts.
Crazy Mts.
Crazy Mts.
Crazy Mts.
Castle Mts.
Castle Mts.
Castle Mts.
Beartooth Mts
Highland Mts.
Highland Mts.
Pioneer Mts.
Flint Creek Mts.
Flint Creek Mts.


Rock Type based on Estimated Modal
Granitoid
Granitoid
Granitoid
Granitoid
Granitoid
Amphibole-Plagioclase Cumulate
Granitoid
Granitoid
Granitoid
Granitoid (Archean Basement)
Granitoid (Monzogranite, Ruppel et al., 1993)
Granitoid (Granodiorite, Ruppel et al., 1993)
Granitoid
Granitoid (Granodiorite/granite, Lewis, 1998)
Granitoid (Quartz monzonite, Lewis, 1998)
Rock Type based on CIPW Normative


Syenite
Granite/syenogranite
Alkali-feldspar syenite
Monzogabbro
Monzonite
Alkali-feldspar syenite
Alkali-feldspar granite
Quartz syenite
Quartz monzonite
Monzogabbro
Alkali-feldspar granite
Alkali-feldspar granite
Quartz monzodiorite
Alkali-feldspar quartz syenite
Alkali-feldspar syenite


Mineral Assemblages
Plag, qtz, k-spar, amph
K-spar, plag, qtz
Plag, k-spar, qtz, amph, bt
Plag, amph, qtz
Plag, qtz, bt
Plag, amph, bt
Plag, k-spar, qtz, bt
K-spar, plag, qtz
Plag, qtz, k-spar, amph
Plag, k-spar, qtz, amph, bt
Plag, k-spar, qtz, bt, amph
Qtz, plag, k-spar, bt
Plag, qtz, k-par, bt, amph
Plag, qtz, k-spar, bt, amph
Plag, k-spar, qtz, amph, bt, pyr
Mineral Assemblaces A-P-Q


K-spar, qtz, plag
K-spar, qtz, plag
Qtz., k-spar, plag
Plag, k-spar, qtz
Plag, k-spar, qtz
Plag, K-spar, ol
K-spar, Qtz, Plag
K-spar, Qtz, Plag
Plag, k-spar, qtz
Plag, k-spar, qtz
Plag, qtz, k-spar
Plag, qtz, k-spar
Plag, k-spar, qtz
K-spar, qtz, plag
Plag, k-spar, qtz


Latitude
46.460
46.964
47.076
46.042
46.042
46.040
46.456
46.447
46.424
45.008
45.870
45.833
45.820
46.315


Longitude
111.248 W
110.756 W
110.637 W
110.289 W
110.289 W
110.274 W
110.685 W
110.682 W
110.589 W
109.521 W
112.449 W
112.361W
113.273 W
113.251W


Mineral Assemblages
Ab, Or, Qz, An, Hy, Mt, Di, Ap
Ab, Or, Qz, An, Hy, Co, Mt, Ap, II
Ab, Or, An, Hy, Qz, Di, II, Mt, Ap
Ab, Hy, An, Or, Di, Qz, II, Mt, Ap
Ab, Or, An, Hy, Qz, Di, II, Mt, Ap
An, Ab, 01, Di, Or, II, Mt, Ap
Ab, Qz, Or, An, Hy, Co
Ab, Or, Qz, An, Hy, Mt, Ap, II
Ab, Or, Qz, An, Hy, Di, Mt, Ap, II
Ab, An, Hy, Or, Qz, Di, Mt, II, Ap
Ab, O, Qz, An, Hy, Mt, II
Ab, Qz, Or, An, Hy, Mt
Ab, An, Or, Qz, Hy, Mt, II, Ap, Co
Ab, An, Or, Qz, Hy, Di, Mt, II, Ap
Ab, Or, An, Hy, Di, Qz, Mt, II, Ap


Alteration
little-none
little-none
little-none
little-none
little-none
none
moderate
moderate
litte-moderate
litte-moderate
little-none
little-none
none
little-none
moderate











Table 3-3. Whole rock isotopic data
BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02
8Sr/86Sr 0.706476 0.707633 0.706713 0.706042 0.705567 0.706065 0.708586 0.707956
87Sr/86Srnitial 0.706350 0.706966 0.706106 0.705918 0.705331 0.706024 0.705625 0.707677
8Rb/86Sr 0.129685 0.686737 0.625005 0.127486 0.242982 0.042316 3.051352 0.287715
Sr ppm 1651.88 570.15 794.96 823.49 805.57 1228.19 110.26 507.86
Rb ppm 74.0359 135.318 171.715 36.2823 67.6478 17.9617 116.245 50.4993
143Nd/144Nd 0.511976 0.511719 0.511891 0.511899 0.511949 0.511911 0.512219 0.511381
143Nd/144Nd inital 0.511943 0.511695 0.511864 0.511865 0.511921 0.511873 0.512187 0.511353
147Sm/144Nd 0.101412 0.072506 0.082080 0.104049 0.084673 0.116912 0.098750 0.084862
ENd -12.91 -17.93 -14.57 -14.42 -13.44 -14.18 -8.17 -24.52
ENd initial -12.307 -17.137 -13.842 -13.826 -12.727 -13.675 -7.59 -23.81
T(DM) 1.45 1.43 1.33 1.59 1.29 1.78 1.10 1.97
Nd ppm 15.1589 41.6829 48.263 29.8258 45.363 35.355 28.11 24.829
Sm ppm 2.542 4.997 6.55 5.1312 6.35104 6.835 4.59 3.4839
208Pb/204Pb 37.92 37.80 37.49 36.92 36.71 36.99 37.16 37.03
207Pb/204Pb 15.50 15.45 15.39 15.35 15.28 15.35 15.38 15.32
206pb/204Pb 18.07 17.38 16.85 16.41 16.08 16.43 16.77 16.44
CA03 BT03 HM01 HM02 PMO1 FC01 FC02
8Sr/86Sr 0.706312 0.713812 0.707713 0.707345 0.711666 0.709967 0.705934
87Sr/86Srinitial 0.705846 0.713575 0.707132 0.706788 0.710057 0.709441 0.705606
8Rb/86Sr 0.480585 0.244134 0.598309 0.573704 1.656621 0.541330 0.337581
Sr ppm 467.44 589.10 624.80 513.65 133.10 505.02 515.70
Rb ppm 77.6379 49.7044 129.194 101.843 76.2067 94.4811 60.1665
143Nd/144Nd 0.511579 0.510671 0.511826 0.511708 0.511826 0.511854 0.511869
143Nd/144Nd nital 0.511554 0.511785 0.511657 0.511784 0.511808 0.511813
147Sm/144Nd 0.076819 0.099056 0.090201 0.10218 0.091726 0.101200 0.121629
ENd -20.66 -38.37 -15.84 -18.219 -15.84 -15.29 -15.00
ENd initial -19.896 -14.89 -17.38 -14.91 -14.44 -14.33
T(DM) 1.63 3.20 1.50 1.83 1.52 1.61 1.94
Nd ppm 26.594 38.624 33.813 18.9877 28.821 26.092 19.137
Sm ppm 3.3779 6.326 5.043 3.2079 4.371 4.366 3.849
208Pb/204Pb 36.44 43.18 38.29 37.89 38.86 38.43 38.03
207Pb/204Pb 15.22 16.04 15.55 15.41 15.63 15.59 15.50
206Pb/204Pb 15.68 19.80 17.98 17.02 18.82 18.34 17.70













O Beartooth Mtns.
O Eastern Samples
* Western Samples


100

90


Granite


Ab 0 10 20 30 40 50 60 70 80 90 100 Or

Figure 3-1. The classification of granitoids based on their molecular normative An-Ab-Or
composition after Barker (1979) (heavy lines) and O'Connor (1965) (dotted lines)
from Rollinson (1991).

















O Eastern Samples
* Western Samples




0

4



0*


0


65



5 -
5


SiO2

Figure 3-2. Total alkali vs. SiO2, shows the chemical variation within the dataset. Note that the
eastern samples are alkaline and the western samples are calc-alkaline. The
plagioclase-amphibole cumulate from the Crazy Mountains (CZ 05) has been
excluded.


-











10000


1000





100


0












0
Rb Ba Th U Nb Ta K La Ce Pb Pr Sr P Nd Zr Hf Sm Eu Ti Dy Y Ho Yb Lu

Figure 3-3. Trace element abundance diagrams, normalized to N-MORB (Sun and McDonough,
1989). The plagioclase-amphibole cumulate from the Crazy Mountains (CZ 05) has
been excluded. The depletion in HFSE such as Nb indicate that the magmas were
likely generated in a convergent margin setting and/or were derived from an ancient
subduction environment.








































La Ce Pr Nd Sm Eu Tb Dy Ho Er Yb Lu
REE


SRare earth element (REE) abundances normalized to chondritic meteorite values
(Sun and McDonough, 1989). The plagioclase-amphibole cumulate from the Crazy
Mountains (CZ 05) has been excluded. The enrichment in HREE is less than 10x
chondrites and suggests a lower crustal source containing garnet, amphibole, and
possibly pyroxene. The lack of Eu anomalies also indicates that the source material
was not in equilibrium with plagioclase.


10








1--




Figure 3-4


-














O Eastern Samples
Western Samples
o Archean Basement




o


0
ot'





O[


0.704 0.706 0.708 0.710 0.712 0.714
0.704 0.706 0.708 0.710 0.712 0.714


0.716


87 Sr86Sr
S r Initial


Initial 87Sr/86Sr and ENd variation diagram calculated at 50 Ma. for the eastern
samples and at 70 Ma. for the western samples; the value for the Beartooth gneiss
sample is calculated at 50 Ma.


-10



-20-


-30 -



-40
0.7'


02


Figure 3-5.

















15.6 A-"

A 1 -

15.5 A
0. -

a



..'
15.3


-'A
15.2
.' Age = 2082160 Ma

15.1
15 16 17 18 19
206p b204Pb


Figure 3-6. Whole rock Pb isotopic plot showing linear array of sample data from eastern and
western sample sets. Linearity of the array can be interpreted in terms of a common
age of -2.0 Ga for the source of all samples. The "age" of the source is essentially
the same as the oldest Proterozoic ages of the exposed basement in the Little Belt
Mountains (Mueller et al., 2002).













12 CZ 03

10

8

6




14











14
,, CZ05






14

12 BT 03

10

B

6

4

2

K1 % 0 vi %
8? ^ ^*s ? T"^ ^ >n ^ ,* <


CZ 04











1!, .. .. . .. .. .. .
'v NI^ iL$ iv i v y ^ A



HM 02








I ..II . %
~i Nhih;


Figure 3-7. Individual zircons from the Crazy (CZ 03-05), the Highland (HM 02) and the
Beartooth Mountains (BT 03) were analyzed via La-ICP-MS. The Hf model age
(TDM) is compared to the whole rock Nd model age (TDM) shown as a diamond
symbol. The bin size is 0.1 Ga and spans from 1.0 Ga to 3.4 Ga.









CHAPTER 4
DISCUSSION

Major Elements

Major element abundances and petrographic analysis are essential for rock classification,

as well as for providing insight into petrogenesis and source. These rocks exhibit many of the

mineralogical and chemical characteristics of I-Type granites as defined by Chappell and White

(1974). Mineralogically, the relative abundance of amphibole compared to biotite and the

observed lack of muscovite, support the I-type classification of these samples. S-type granites

are characterized by higher mica abundance, especially muscovite. I-Type granites also yield

abundant magnetite (instead of ilmenite) and pink and white alkali feldspars, both of which are

present in the sample set. Additionally, the presence of mafic enclaves in outcrops in the Big

Belt Range, Highland Mountains, and the Pioneer Mountains indicate a non S-type source.

Chemically, these samples also correspond to I-type granites in CaO, Na20, and Sr

concentrations (Table 3-1). The average values of 3.68 weight percent, 4.06 weight percent, and

711 ppm respectively are too high to correspond to S-type granites (Bowden, 1984). In addition,

the CIPW normative mineralogy demonstrates that the average amount of quartz is below the

amounts typically found in S-type rocks, and that the amount of corundum is within the limits

(below 1.0) of an I-type granite (Table 3-1). This evidence is compatible with petrogenesis

involving a mafic, metaigneous source.

Trace Elements

Trace element concentrations help provide estimates of the source material composition,

the residual minerals left behind by melt extraction, and the extent of melt mixing and source

variability. The REE patterns in all rocks show enrichment in LREE and a corresponding less

enriched distribution of HREE, characteristic of continental granitoids (Pearce, et al., 1984;









Winter, 2001). The enrichments in HREEs are less than 10x chondrites, suggesting a lower

crustal source potentially containing one or more of the following: garnet, amphibole, and/or

pyroxene. Y and Yb, however, are concentrated in garnet, and the lack of any negative Y or Yb

anomaly again suggests that the magma sources) was not garnet-bearing (Figures 3-3 and 3-4).

The lack of Eu anomalies indicate that plagioclase was absent from the source, that the source

had not previously undergone a significant feldspar fractionation cycle (Halliday and Stephens,

1984), and that plagioclase fractionation had very limited impact on magmatic evolution in these

samples. This provides further evidence of a mantle and/or lower crust source that lacked an

upper crustal history. LILEs (large ion lithophile elements) are also incompatible and behave

similarly to the HFSE in solid-melt exchange, but behave differently in the presence of an

aqueous fluid. Given that this dataset shows enrichment in Rb, Ba, and Pb, but lesser

enrichments in the HFSE, a high LILE/HFSE ratio results (Figure 3-3). The decoupling of these

two chemical groups is best explained by the participation of water-rich fluids in the genesis of

subduction zone magmas (e.g., Hanson, 1978; Winter, 2001). Depletion in HFSEs and Nb in

particular indicate that the magmas were likely generated in a convergent margin setting, were

derived from rocks produced in an ancient subduction environment (Morris and Hart, 1983;

Saunders et al., 1991), or some combination of the ancient subducted material and the younger

Cretaceous/Tertiary subduction.

Major and trace element abundances for these intermediate granitoids, therefore, strongly

suggest that the samples were derived primarily, if not exclusively, from a mafic, meta-igneous,

lower crustal source. The stimulus for melting in both the eastern and western regions is likely

related to Farallon plate subduction, despite the alkalic vs. calc-alkalic nature of the rocks from

the eastern and western groups respectively (Coney & Reynolds, 1977; Humphreys et al., 2003).









An alternate option is that the lower crustal source formed in a subduction environment related to

the collision between the Wyoming Province and the Medicine Hat Block. This ambiguity of the

age of the source and potential mixing of Farallon-derived fluids or magmas derived from an

ancient subduction generated mafic lower crust cannot be resolved with trace element data alone.

Age of the Lower Crust

Regardless of their petrochemical composition, contemporaneous intrusions emplaced in

similar country-rocks and derived from similar sources can be expected to show very similar Sr-

Nd-Pb-Hf isotopic systematics. Measurements of present day isotopic values, particularly for Sr,

Nd, and Pb, can be used to calculate the initial isotopic ratios for the source material. These

calculated initial values are useful for determining both petrogenetic and model age information

about the source. Initial Sr isotopic values range from 0.705-0.710, generally compatible with an

ancient crustal origin (e.g., Arth et al., 1986, Mueller, et al., 1997). Figure 3-5 shows initial

87Sr/86Sr and ENd ratios are generally correlative and the negative ENd values strongly indicate

that there was involvement of an older, enriched source.

Sm and Nd are far less susceptible to fractionation during melting and subsequent

alteration than are Rb and Sr and, as a result, the 143Nd/144Nd ratio can be used to provide a more

reliable indicator of the age of the material in the source regionss. The range of Sm/Nd model

ages generated by these rocks suggests that the sources) are likely to be both compositionally

and chronologically heterogeneous. Although the actual TDM are scattered from 1.1-1.9 Ga, this

range is well within the temporal boundaries of the Proterozoic, indicating that there is not likely

to be significant involvement of Archean crust. It is important to note that the upper limit of this

range corresponds with the oldest basement rock U/Pb zircon age date determined for the Little

Belt Mountains at -1.9 Ga (Mueller et al., 2002) and is therefore unlikely to be a fortuitous

mixture of Archean and younger crust.









The heterogeneity seen in the Rb-Sr and Sm-Nd systematics is not evident in the Pb-Pb

system. A whole rock Pb isotopic plot (Figure 8) produces a linear array that suggests a

Paleoproterozoic source. Extensive recent mixing to produce a homogenous array for individual

plutons over this large of an area seems unlikely; therefore, mixing and establishment of the

diverse U/Pb ratios needed to form the array was more likely to have been in the Proterozoic.

These whole rock Pb isotopic data, therefore, suggest that this lower crustal source is likely

Proterozoic and that -2.0 Ga is a reasonable approximation of its age (Figure 3-6). An "age" of

-2.1 Ga compares favorably with the age of the oldest Proterozoic rocks in the area (-1.9 Ga;

Mueller et al., 2002) and the oldest Sm-Nd model ages.

As noted above, the Sm-Nd model ages are not consistently Paleoproterozoic. Some of

this variability is likely due to heterogeneities in the source region, variable fractionation of Sm

and Nd, and/or mixing between sources (Mueller et al., 1995, 1996). Sm-Nd model ages suggest

some mixing of the Proterozoic sources) characteristic of the Pb array with a younger

asthenospheric Nd component. The older component may approximate the -1.9 Ga basement

age from the Little Belt Mountains and the other may be derived from fluids liberated by

Farallon subduction. The primary reason for the difference in response of the Sm-Nd and Pb-Pb

systems during petrogenesis of individual rocks is directly related to the smaller differences in

the elemental abundances of Sm and Nd compared to Pb elemental abundances between the

mantle and crust. This differential makes for a more homogeneous, more crust-dominated

response of the Pb system than the Sm-Nd system in crustal environments.

Further constraints on the age of the source are provided by Lu/Hf isotopic ratios preserved

in zircon crystals formed during the crystallization of the granitoid melts or directly inherited

from the source. The Lu/Hf system is similar to the Sm/Nd system in providing insight into









petrogenetic and crustal processes, with the advantage of yielding numerous analyses from

zircon crystals rather than the averaging represented by whole-rock Sm-Nd data. These Hf

values provide a "snapshot" of the isotopic composition of the melt (and hence source region)

itself and, in some cases, zircons inherited from that source or sources are likely to remain

largely undisturbed by incorporation in the melt or subsequent weathering, hydrothermal, or

other alteration processes. This effect is observed in the Highland Mountains (sample HM02),

where the Nd model age (TDM) is -1.8 Ga and correlates well with the primary Hf model age

(TDM) data, but fails to identify two additional Hf model age populations detected at -1.4 Ga and

-2.8 Ga (Figure 3-7).

Tectonics

The geochemical data presented above suggests that the primary components) of the lower

crust within the GFTZ is Proterozoic, generated as juvenile crust in a convergent setting (e.g.,

Mueller et al., 2002). The addition of individual zircon analyses reveal that the Highland

Mountains in the western portion of the study area contain an additional zircon population

characterized by an Archean Hf model age. Samples in the eastern region do not possess zircons

with an Archean signature. The zircon Hf data from the Highland Mountains seems to indicate

the presence of Archean crust at depth mixed with a Paleoproterozoic component. This would

suggest that the collision between the Medicine Hat Block and the Wyoming province was not

between parallel margins. Instead, these data support the idea of an oblique convergence along

the Medicine Hat and Wyoming Province that produced relatively more juvenile crust in the

central GFTZ and more reworked Archean crust in the western GFTZ, as suggested by Mueller

et al. (2005). This pattern of reworked Archean crust in the Highland Mountains suggests a point

of collision between the Wyoming Province and Medicine Hat block in this region, reworking

slivers of Archean crust into the juvenile crust of the Paleoproterozoic. The absence of this









direct collision in the east is inferred by the presence of only Paleoproterozoic Hf model ages

seen in samples from this region. Later convergence in the GFTZ was then accommodated by

increasing strike-slip translation (Mueller et al, 2005).

The argument that the GFTZ is not a collisional boundary, but instead an intracratonic

shear zone reactivated during the Trans-Hudson Orogeny (Boerner, 1998), becomes less tenable

given the results of this study because shear zones are not typically characterized by magmatism,

particularly the formation of juvenile crust. The geochemical data presented above indicate that

active magmatism was occurring during the formation of the GFTZ in the Paleoproterozoic. The

trace elemental data, particularly HFSE depletion, strongly suggest a convergent margin setting

for generation of the present lower crust. The age constraints provided by isotopic model ages

strongly suggest that the trace element signal largely developed in the Paleoproterozoic.

Understanding the tectonic evolution of the GFTZ provides insight into the identity of the

conjugate margins of Laurentia in Rodinia paleoreconstructions. SWEAT and AUSWUS

reconstructions (Jefferson, 1978; Moores, 1991; Hoffman, 1991; Ross et al., 1992; Burrett and

Berry, 2000; Karlstrom et al., 2001) primarily rely on matching the Proterozoic Yavapai,

Mazatzal, and Grenville belts on the southwestern Laurentian margin with similar-age orogenic

provinces in Australia or Antarctica. Borg and DePaolo (1994) observed that these

reconstructions are dependent on the geochronology and isotopic mapping that defines each of

these provinces and suggested a possible role for an Antarctica-Idaho connection. The SWEAT

and AUSWUS models are difficult to uniquely test on the basis of these correlations due to the

widespread distribution of 1.7-1.0 Ga accretionary and collisional belts. These widespread,

similarly aged belts, therefore, are limited in utility as piercing points for reconstructions. Sears

and Price (1978; 2000; 2003) argue for a Siberia-Laurentia connection. Dikes and sills in the









Wyoming Province and Anabar shield of Siberia appear to share similar ages of emplacement at

-1500 Ma (Sears and Price, 2003). The Belt-Purcell basin shows many similarities with the

Udzha basin of Siberia, as Sears and Price (2003) note the seemingly continuous pattern of

sediment transport and provenance. Sears et al. (2004) also note an intriguing correlation

between the GFTZ and the Aekit terrane of Siberia, which they argue separated during the

opening of the Belt-Purcell/Udzha basin. This may provide the first robust target for detailed

isotopic mapping on a possible conjugate margin. An isotopic study of the Siberian Aekit

terrane would test the validity of this Siberian-Laurentia model. An additional target for detailed

isotopic studies is provided by Burrett and Berry (2000) who connect the GFTZ with the

Diamantina Lineament located in Australia (i.e. AUSWUS reconstruction). Without such data,

however, refined isotopic data from the GFTZ can be used to identify a unique piercing point to

better evaluate the conjugates proposed by these models. Isotopic studies conducted on the

potential conjugate margins) will help evaluate each, as the mix of Archean and

Paleoproterozoic crust forming the GFTZ should serve as an excellent diagnostic marker.









CHAPTER 5
CONCLUSIONS

Detailed geochemical analyses conducted on Cretaceous-Tertiary granitic plutons within

the GFTZ provide valuable insight into the composition of the lower crust in the GFTZ and its

tectonic origin. These plutons are all I-type granites, derived from the melting of a

predominantly mafic, ancient, lower crustal sources) that originally formed as the result of

subduction. Isotopic data (Sr, Nd, Pb, and Hf) suggest that the lower crust is Paleoproterozoic in

age, indicating that new lower crust was being generated during this time interval, which is

conducive to viewing the GFTZ as a collisional suture zone. These characteristics of the GFTZ

make it a more important piercing point for, assessing Rodinia reconstruction models.









LIST OF REFERENCES


Arth, J.G., Zen, E-an, Sellers, F. and Hammarstrom, J., 1986, High initial Sr isotopic ratios and evidence
for magma mixing in the Pioneer batholith of southwest Montana: Journal of Geology, v. 94, p.
419-430.

Barker, F., 1979, Trondhjemite: Definition, environment and hypotheses of origin, in, Trondhjemites,
dacites, and related rocks: edited by Barker, F., Elsevier, Amsterdam, p.1-12

Bennet, V., and DePaolo, D.J., 1987, Proterozoic crustal history of the western United States as
determined by neodymium isotopic mapping: Geological Society of America Bulletin, v. 99, p.
674-685.

Boerner, D.; Craven, J.; Kurtz, R.; Ross, G.; and Jones, F. 1998, The Great Falls tectonic zone: Suture or
intracontinental shear zone?: Canadian Journal of Earth Science, v. 35, p. 175-183.

Borg, S.G., and DePaolo, D.J., 1994, Laurentia, Australia, and Antarctica as a late Proterozoic
supercontinent: constraints from isotopic mapping: Geology, v. 22, p. 307-310.

Bowden, P, Batchelor, R.A., Chappell, B.W., Didier, J., and Lameyre, J., 1984, Petrological,
geochemical, and soure criteria for the classification of granitic rocks: A discussion: Physics of
the Earth and Planetary Interiors, no. 35, p 1-11.

Burrett, C., and Berry, R., 2000, Proterozoic Australia-Western United States (AUSWUS) fit between
Laurentia and Australia: Geology, v. 28, p. 103-106.

Chappell, B.W., White, A.J.R., 1974, Two contrasting granite types: Pacific Geology, v. 8, p. 173-174.

Coney, P.J., and Reynolds, S.J., 1977, Flattening of the Farallon slab: Nature, v. 270, p. 403-406.

Coyner, S.J., Kamenov, G.D., Mueller, P.A., Rao, V., Foster, D.A., 2004, FC-1: A zircon reference
standard for the determination of Hf isotopic compositions via laser ablation ICP-MS: Eos
Trans., AGU, 85 (47), Fall Meet. Suppl., V51C-0584.

Dahl, P. S., Holm, D. K.; Gardner, E. T., Hubacher, F. A., and Foland, K. A., 1999, New constraints on
the timing of Early Proterozoic tectonism in the Black Hills (South Dakota), with implications
for docking of the Wyoming province with Laurentia: Geological Society of America Bulletin, v.
ll, p. 1335-1349.

DePaolo, D.J., 1988, Age dependence of the composition of continental crust: Evidence from Nd
isotopic variations in granitic rocks: Earth and Planetary Science Letters, v. 90, p. 263-271.

Dickinson, W.R., 1981, Plate tectonics of the continental margin of California, in The Geotectonic
Development of California: edited by W.G. Ernst, Prentice-Hall, Englewood Cliffs, N.J., 706 pp.

Dudas, F. 0.; Carlson, R. W.; and Eggler, D. H. 1987, Regional middle Proterozoic enrichment of the
subcontinental mantle source of igneous rocks from central Montana: Geology, v. 15, p. 22-25.










Farmer, G.L. and DePaolo, D.J., 1983, Origin of Mesozoic and Tertiary granite in the western United
States and implications for pre-Mesozoic crustal structure 1. Nd and Sr isotopic studies in the
geocline of the northern Great Basin: Journal of Geophysical Research, v. 88, no. B4, p. 3379-
3401.

Foster, D.A., P.A. Mueller, D.W. Mogk, J.L. Wooden, and J.J. Vogl, 2006, Proterozoic evolution of the
western margin of the Wyoming Craton: Implications for the tectonic and magmatic evolution of
the northern Rocky Mountains: Canadian Journal of Earth Sciences, v. 43, p. 1601-1619.

Gallet, Y. and Pavlov, V.E., Semikhatov, M.A., and Ptrov, P.Y., 2000, Late Mesoproterozoic
magnetostratigraphic results from Siberia: Paleogeographic Implications and magnetic field
behaviour: Journal of Geophysical Research, v. 105, p. 16481-16499.

Gunn, S.H., 1991, Isotopic Constraints on the crustal evolution of southwestern Montana. Ph.D.
Dissertation, University of California at Santa Cruz, 204pp.

Halliday, A.N., and Stephens, W.E., 1984, Crustal controls on the genesis of the 400 Ma old Caledonian
granites: Physics of Earth and Planetary Interiors, v. 35, p. 89-104.

Hanson, G.N., 1978, The application of trace elements to the petrogenesis of igneous rocks of granitic
composition: Earth and Planetary Science Letters, v. 38, p. 26-43.

Harlan, S.S., Geissman, J.W., Lageson, D.R., and Snee, L.W., 1988, Paleomagnetic and isotopic dating
of thrust belt deformation along the eastern edge of the Helena salient, northern Crazy
Mountains, Montana: Geological Society of America Bulletin, v. 100, p. 492-499.

Heatherington, A., Mueller, P.A., 1991, Geochemical evidence for Triassic rifting in southwestern
Florida: Tectonophysics, v. 188, p. 291-302.

Hoffman, P., 1988, United Plates of America, the birth of a craton: Annual Review of Earth and
Planetary Science, p. 16543-16603.

Hoffman, P.J., 1991, Did the breakout of Laurentia turn Gondwanaland inside-out?: Science, v. 252, p.
1409-1412.

Humphreys, E., Hessler, E., Dueker, K., Farmer, G.L., Erslev, E. and Atwater, T. 2003, How Laramide-
age hydration of North American lithosphere by the Farallon slab controlled subsequent activity
in the western United States: International Geology Review, v. 45, p. 575-595.

Jefferson, C.W., 1978, Correlation of middle and upper Proterozoic strata between northwestern Canada
and south and central Australia [abs.]: Geological Association of Canada Program with
Abstracts, v. 13, p. 429.









Kamenov, G.D., Mueller, P., and Perfit, M., 2004, Optimization of mixed Pb-Tl solutions for high
precision isotopic analyses by MC-ICP-MS: Journal of Analytical Atomic Spectrometry, v.19,
no. 9, p. 1262-1267.

Karlstrom, K.E., Ahall, K.L., Harlan, S.S., Williams, M.L., McLelland, J., and Geissman, J.W., 2001,
Long-lived (1.8-1.0 Ga) convergent orogen in southern Laurentia, its extensions to Australia and
Baltica, and implications for refining Rodinia: Precambrian Research, v. 111, p. 5-30.

Kistler, R.W., and Peterman, Z.E., 1973, Variations in Sr, Rb, K, Na, and initial 87Sr/86Sr in Mesozoic
granitic rocks and intruded wall rocks in central California: Geological Society of America
Bulletin: v.84, p. 3489-3512.

Lewis, R.S., 1998, Geologic map of the Butte 1 x 2 quadrangle, Montana: Montana Bureau of Mines
and Geology Open File MBMG 363.

Ludwig, K. R. 2003. User's manual for Isoplot 3.00 (Berkeley Geochronology Center Special
Publication 4. Berkeley Geochronology Center.

Meert, J.G. and Torsvik, T.H., 2003. The making and unmaking of a supercontinent: Rodinia Revisited:
Tectonophysics, v. 375, p. 261-288.

Mogk, D.W., Mueller, P.A., and Wooden, J.L., 1992, The nature of Archean terrane boundaries: An
example from the northern Wyoming Province: Precambrian Research, v. 55, p. 155-168.

Moores, E.M., 1991, Southwest U.S.East Antarctic (SWEAT) connection: A hypothesis: Geology, v. 19,
p. 425-428.

Morris, J.D., and Hart, S.R., 1983, Isotopic and incompatible trace element constraints on the genesis
of island arc volcanics from Cold Bay and Amak Island, Aleutians, and implications for mantle
structure: Geochimica et Cosmochimica Acta, v. 47, p. 2051-2030.

Mueller, P.A., Shuster, R.D., D'Arcy, K.A., Heatherington, A.L., Nutman, A.P., Williams, I.S., 1995,
Source of the northeastern Idaho Batholith: Isotopic evidence for a Paleoproterozoic terrane in
the northwestern U.S.: Journal of Geology, v. 103, p. 63-72.

Mueller, P.A., Heatherington, A.L., D'Arcy, K.A., Wooden, J.L., and Nutman, A.P., 1996, Contrasts
between Sm-Nd whole rock and U-Pb zircon systematics in the Tobacco Root batholith,
Montana: Implications for the determination of crustal age provinces: Tectonophysics, v. 265, p.
169-179.

Mueller, P., Wooden, J. Heatherington, A., and Nutman, A., 1997, Distribution of Proterozoic crust
along the NW margin of cratonic North America: evidence from U-Pb zircon ages and isotopic
systematics in young granitoids: Geological Society of America Abstracts with Programs, v. 29,
p. A-70.









Mueller, P., Heatheringtons, A., Kelley, D., Wooden, J., Mogk, D., 2002, Paleoproterozoic crust within
the Great Falls Tectonic Zone: Implications for the assembly of southern Laurentia: Geology, v.
30, p. 127-130.

Mueller, P.A., Burger, H.R., Wooden, J.L., Brady, J.B., Cheney, J.T., Harms, T.A., Heatherington, A.L.,
Mogk, D.W., 2005, Paleoproterozoic metamorphism in the northern Wyoming Province:
Implications for the assembly of Laurentia: Journal of Geology, v. 113, p. 169-179.

Mueller, P., Foster, D., Mogk, D., Wooden, J., and Vogl, J., 2007, Provenance of the Uinta Mountain
Group from Pb and Hf isotopic compositions of detrital zircons: Geology, v. 35, n. 5, p.431-434.

O'Connor, J.T., 1965, A classification for quartz-rich igneous rock based on feldspar ratios: USGS
Professional paper 525B, p. B79-B84.

O'Neill, J. and Lopez, D., 1985, Character and regional significance of Great Falls tectonic zone, East-
Central Idaho and West-Central Montana: American Association of Petroleum Geologists
Bulletin, v. 69, p. 437-447.

Pearce, J.A., N.B.W., Harris, and Tindle, A.G., 1984, Trace element discrimination diagrams for the
tectonic implications of granitic rocks: Journal of Petrology, v. 25, p. 956-983.

Pesonen, L.J., Elming, S.A., Mertanen, S., Pisarevski, S., D'Agrella-Filho, M.S., Meert, J., Schmidt,
P.W., Abrahmsen, N., Bylund, G., 2003, Assemblies of continents during the Proterozoic:
Rodinia and beyond: Tectonophysics, v. 375, p. 289-324.

Ross, G.M., Parrish, R.R., and Winston, D., 1992, Provenance and U-Pb geochronology of the
Mesoproterozoic Belt Supergroup (northwestern United States): Implications for age deposition
and pre-Panthalassa plate reconstructions: Earth and Planetary Science Letters, v. 113, p. 57-76.

Ruppel, E.T., O'Neill J.M., and Lopez, D.A., 1993, Geologic Map of the Dillon lx20 quadrangle, Idaho
and Montana: U.S. Geological Survey Map I-1803-H.

Saunders, A.D., Norry, M.J., and Tarney, J., 1991, Fluid influence on the trace element composition of
subduction zone magmas: Philosophical Transactions of the Royal Society of London, v. 335, p.
377-392.

Sears, J.W., and Price, R.A., 1978, The Siberian connection: A case for the Precambrian separation of
the North American and Siberian cratons: Geology, v. 6, p. 267-270.

Sears, J.W., and Price, R.A., 2000, New look at the Siberian connection: No SWEAT: Geology, v 28, p.
423-426.

Sears, J.W., and Price, R.A., 2003, Tightening the Siberian connection to western Laurentia: Geological
Society of America Bulletin, v. 115, no. 8, p. 943-953.









Sun, S.S. and McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts:
implications for mantle composition and processes, In Saunders, A.D. and Norry, M.J. (eds.),
Magmatism in ocean basins: Geological Society of London Special Publication, no.42, p. 313-
345.

Wingate, M.T.D., Pisarevsky, S.A. and Evans, D.A.D., 2002, Rodinia connections between Australia
and Laurentia: No SWEAT, no AUSWUS?: Terra Nova, v. 14, p. 121-128.

Winter, J.D., 2001, An introduction to igneous and metamorphic petrology: Prentice Hall, Upper Saddle
River, N.J., 697pp.

Wooden, J.L., and Mueller, P.A., 1988, Pb, Sr, and Nd isotopic compositions of a suite of late Archean,
igneous rocks, eastern Beartooth Mountains: Implications for crust-mantle evolution: Earth and
Planetary Science Letters, v. 87, p. 59-72.

Wooden, J.L., and Miller, D.M., 1990, Chronologic and isotopic framework for early Proterozoic crustal
evolution in the eastern Mojave Desert region, SE California: Journal of Geophysical Research,
v. 95, no., B12, p. 20133-20146.

Zartman, R.E., 1974, Lead isotopic provinces in the Cordillera of the western United States and their
geologic significance: Economic Geology, v. 69, p. 792-805.

Zartman, R.E., 1988, Proceedings of the international Conference on Basement Tectonics, v.8, p. 699-
710.









BIOGRAPHICAL SKETCH

Kelly R. Probst was born in Indianapolis, Indiana, in 1979. She graduated from the

Business & Finance Magnet Program at Northwest High School in 1997 with National Honors.

While attending Indiana University-Purdue University at Indianapolis, she engaged in

undergraduate research in the geologic sciences and received her B.S. in geology in 2004. While

attending the University of Florida, she served as a graduate teaching assistant in the Department

of Geological Sciences and also acted as department representative for the Graduate Student

Council 2006-2007. After completing her first year of graduate work, she accepted an internship

in the mining industry, where she discovered her interest upon graduating. She intends to pursue

a professional career in economic/industrial geology after receiving her Master of Science.





PAGE 1

1 GEOCHEMISTRY OF CRETACEOUS AND TERTIARY PLUTONS OF THE GREAT FALLS TECTONIC ZONE: IMPLICAT IONS FOR CRUSTAL EVOLUTION By KELLY R. PROBST A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2007

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2 2007 Kelly R. Probst

PAGE 3

3 Dedicated to Norton and Higgins

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4 ACKNOWLEDGMENTS This research was funded by the Tobacco Root Geologic Society, the Colorado Scientific Society, National Science Foundation (EAR 010 6592), and the USGS (05HQGR0156). We thank Jim Vogl, David Foster, David Mogk, and Jo sh Richards for their assistance in sample collection, Sam Coyner for his guidance in samp le preparation, Darryl Henry for CL and SEM images of the zircon crystals, and to David Foster, Joe Meert, and Shawn Malone for their insightful reviews.

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5 TABLE OF CONTENTS page ACKNOWLEDGMENTS...............................................................................................................4 LIST OF TABLES................................................................................................................. ..........6 LIST OF FIGURES................................................................................................................ .........7 ABSTRACT....................................................................................................................... ..............8 CHAPTER 1 INTRODUCTION..................................................................................................................10 Background..................................................................................................................... ........10 Regional Setting............................................................................................................... .......12 2 METHODS........................................................................................................................ .....15 Sampling Strategy.............................................................................................................. .....15 Geochemical Preparation........................................................................................................15 Mineral Separation............................................................................................................. .....16 Zircon Analysis................................................................................................................ .......17 3 RESULTS........................................................................................................................ .......22 Major Elements................................................................................................................. ......22 Trace Elements................................................................................................................. ......23 Isotopes....................................................................................................................... ............23 Zircons........................................................................................................................ ............24 4 DISCUSSION..................................................................................................................... ....37 Major Elements................................................................................................................. ......37 Trace Elements................................................................................................................. ......37 Age of the Lower Crust......................................................................................................... .39 Tectonics...................................................................................................................... ...........41 5 CONCLUSIONS....................................................................................................................44 LIST OF REFERENCES............................................................................................................. ..45 BIOGRAPHICAL SKETCH.........................................................................................................50

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6 LIST OF TABLES Table page 2-1 Individual zi rcon analyses................................................................................................. .18 3-1 Whole-rock elemental data................................................................................................26 3-2 Sample descriptions........................................................................................................ ...28 3-3 Whole rock isotopic data...................................................................................................29

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7 LIST OF FIGURES Figure page 1-1. Simplified geologic mapof the study area.........................................................................14 2-1. CL image of typical zircon grains from the Highland Mountains (HM 02)..................21 3-1. The classification of granitoids base d on their molecular normative An-Ab-Or composition.................................................................................................................... ....30 3-2. Total alkali vs. SiO2, .........................................................................................................31 3-3. Trace element abundance diag rams, normalized to N-MORB .........................................32 3-4. Rare earth element (REE) abundances nor malized to chondritic meteorite values...........33 3-5. Initial 87Sr/86Sr and Nd variation diagram........................................................................34 3-6. Whole rock Pb isotopic plot...............................................................................................35 3-7. Individual zircons from the Crazy (CZ 03-05), the Highland (HM 02) and the Beartooth Mountains (BT 03) we re analyzed via La-ICP-MS..........................................36

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8 Abstract of Thesis Presen ted to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science GEOCHEMISTRY OF CRETACEOUS AND TERTIARY PLUTONS OF THE GREAT FALLS TECTONIC ZONE: IMPLICAT IONS FOR CRUSTAL EVOLUTION By Kelly R. Probst August 2007 Chair: Paul Mueller Major: Geology Constraining the age of the crust and tecton ic origin of the Great Falls tectonic zone (GFTZ) are important to understanding the accre tionary history of Laurentia. Because the basement of the GFTZ is not well exposed, isotopic and elemental studies of the Cretaceous and Tertiary plutons intruded into this zone provide cons traints on the age and composition of this crust. Trace element, Sr, Nd, and Pb isotopi c compositions of these magmatic rocks show several important characteristics: 1) LREE en richment with minimal Eu anomalies and HREE contents < 10x chondrites indicate a mafic lower crustal source containing garnet, amphibole, and/or pyroxene with little or no plagioclase, 2) Depletion in HFSE (e.g., Nb) suggests this source was originally formed in a conve rgent margin, 3) Sm-Nd model ages (TDM) range from 1.1-1.9 Ga and whole rock Pb isotop es provide a nearly linear arra y at ~2.1 Ga, indicating that Archean crust is unlikely to be involved. Lu/Hf isotopic systematics preserved in zircon grains from individual plutons reveal Paleoproterozoic model ages in all cases. The western Highland Mountains contain an additional zircon populatio n characterized by an Archean model age (~3.0 Ga); there is no evidence of Archean grains wi thin the eastern study area. These observations support models that suggest the GFTZ formed as the result of a collisi on between the Medicine Hat Block and the Wyoming province in the Pale oproterozoic, but that the collision was not

PAGE 9

9 along two parallel margins. Instead, these da ta support the idea of an oblique convergence between the Medicine Hat and Wyoming Provin ce that resulted in the formation of new Paleoproterozoic crust, the rewo rking of Archean crust, and th e imbrication of Archean and Paleoproterozoic crust. Documentation of these re lationships and the tect onic evolution of the GFTZ provide important criteria for identifying th e conjugate margin of western Laurentia in Rodinia paleoreconstructions.

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10 CHAPTER 1 INTRODUCTION Background Many aspects of the evolution of Laurentia remain unclear because the locations of boundaries between many basement age provinces are not well constrained. One outstanding example of this problem is exem plified by the number of extant proposals for the identity of the craton(s) that separated from SW Laurentia during the Neoproterozoic breakup of Rodinia. Australia, South China, and Siberi a have been proposed as this c onjugate, but the paucity of high resolution geologic and paleomagnetic data pr event the development of a unique solution (Burrett and Berry, 2000; Karlstro m et al., 2001; Wingate et al., 2002; Gallet et al., 2000; Sears and Price, 2003; Meert and Torsvik, 2003). One key area that is criti cal to reconstructing Laurentia is the Precambrian basement of the Gr eat Falls tectonic zone (GFTZ). This zone remains poorly characterized because of the lack of basement exposure due to the accumulation of a thick sedimentary cover (e.g., Belt-Purce ll), Mesozoic terrane accretion, and plutonism (ONeil and Lopez, 1985; Mueller, et al., 1995; Boerner et al., 1998,). A potential window into this largely buried basement is available via study of the numerous Mesozoic and Cenozoic plutons within the GFTZ. Extensive plutonism marked the Mesozoic and Cenozoic of the western United States, including the GFTZ, which was probably the result of Farallon Plate subduction beneath the Cordilleran margin (Dic kinson, 1981; Humphreys et al., 2003). The composition of these mostly felsic plutons provides an indirect sample of the Precambrian basement, as suggested by DePaolo, (1988). De Paolo (1988) showed that granitoid rocks can provide a reliable means of sampling the isotopic composition of the deeper parts of the crust. Identifying the petrogenetic processes involved in forming these plutons provides invaluable information about source material and/or in teractions with the intervening crust.

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11 Systematic variations of trace element and is otopic systems provide highly sensitive tools in correlating the chemistry of these young plutonic rocks to th eir petrogenetic processes and sources within mantle and crustal reservoirs (e.g., Farmer and DePaolo, 1983; Zartman, 1988). Early isotopic mapping in the western Unite d States was conducted in the 1970s using 87Sr/86Sr as the primary tool. Kistler and Peterman ( 1973) identified the proposed boundary between cratonic North America and Phanerozoic accreted terranes by mapping Sr isotopic ratios of young plutonic rocks and identified this boundary as the 87Sr/86Sr 0.706 line. They demonstrated that the initial strontium isot opic ratios in young rocks locate d in central California were dependent on geographic location, re flecting the distribution of base ment rocks of differing ages and compositions (Kistler and Peterman, 1973). This approach was expanded by Farmer and DePaolo (1983), who used Sm-Nd systematics to propose that the interac tions of mantle and crust during the genesis of contin ental granitic magmas are influenced by their distance from the continental margin. They conducted a comparativ e Nd and Sr isotopic study across the northern half of the Great Basin of Nevada and Utah to the east of the Great Basin (e.g., spanning from the continental margin to the cratonic interior). It was demonstrated that isotopic signatures of plutons east of the Roberts Mountain Thrust (RMT) are pred ominantly influenced by the Precambrian crystalline basement, whereas plutons west of the RMT are primarily derived from mantle and/or young crustal sources (Farmer and DePaolo 1983). This observation led to their identification of the western edge of the Prec ambrian basement as the RMT, 100-200 km east of the 87Sr/86Sr 0.706 line of Kistler and Peterman (1973). Bennet and DePaolo (1987) extended this ap proach and recognized that identifying the boundary between different crustal age-provinces can provide information about the formation and subsequent modification of the continen ts. Bennet and DePaolo (1987) used Sm-Nd

PAGE 12

12 systematics to compare Nd age provinces to the is otopic Pb provinces of the southwestern United States, previously identified by Zartman (1984). A lthough there are a total of four lead isotopic provinces in the southwestern United States (Zartman, 1974), Nd isotopic mapping delineates only three. In the Wyoming Province, one of the oldest elements of Laurentia, Wooden and Mueller (1988) used a combination of Sr Nd, and Pb systematics and trace element compositions of late Archean igneous rocks of the Beartooth Mount ains to postulate a subduction origin for the voluminous late Arch ean crust of the northern Wyoming Province along with contemporaneous metasomatism of the accompanying mantle wedge. Regional Setting Several workers have proposed that the Wyoming Province collided with the southern edge of the Rae-Hearne craton and/ or the intervening Medicine Hat block as part of a series of orogenic events that led to the assembly of Laurentias main components during the Paleoproterozoic (e.g., ONeil and Lopez, 1985; Hoffman, 1988; Muel ler et al., 2005; Dahl et al., 1999). This collision resulted in the formation of a suture zone, incorporating both juvenile crust formed during convergence as well as reworked Archean crustal elements, and has been labeled the Great Falls tectonic zone (GFTZ; ONeil and Lopez, 1985; Mueller et al., 2002) (Figure 1-1). The proportion of these disparate elements, howev er, is unclear. Juve nile Paleoproterozoic crustal products are documented only in the Little Belt Mounta ins of southwestern Montana (Mueller, et al., 2002). A contrasting interpretation of the GF TZ suggests that the belt of NE-SW trending features of the GFTZ, including magne totelluric patterns, end abruptly at the intersection of the Trans-Hudson orogen in s outhwestern-most Saskatchewan, Canada. These authors (Boerner et al., 1998) c oncluded that the GFTZ is an Ar chean structure that was later reactivated as an intracratonic sh ear zone during the Paleoproterozoic

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13 In this study we use major and trace element, Sr, Nd, and Pb isotopic values of Cretaceous and Tertiary magmatic rocks of intermediate composition (i.e, those lik ely derived from lower crustal sources) and Lu-Hf systematics of zircons to gain insight into th e age and nature of the lower crust within the GFTZ and constrain the tectonic origin of the GFTZ. Although isotopic mapping has been conducted on a large scale th roughout western North America (Kistler and Peterman, 1973; Farmer and DePaolo, 1983; Benne t and DePaolo, 1987), little work has been done to define smaller scale boundaries within this region. The northwestern edge of the Wyoming craton represents one area where detailed spatial resolution is required to assess the role it played during the amalga mation of Laurentia and as a consequence, its importance for testing models for the Rodinia configuration of Laurentia (e.g., Gunn, 1991, Mogk et al., 1992). Using K-T plutons that have been intruded in to the GFTZ as probes of the lower crust will produce a high resolution image of lower crustal composition in this region and provide possibly valuable constraints for both Proterozoic pale ogeographic/paleotectonic reconstructions and for testing proposed conjugate cr atons in Rodinia reconstruc tions (e.g., AUSWUS (Burrett and Berry, 2000; Karlstrom et al., 2001), AUSMEX (W ingate et al., 2002), SI BCOR (Gallet et al., 2000; Sears and Price, 1978, 2000, 2003; Meert and Torsvik, 2003), SWEAT (Jefferson, 1978; Moores, 1991; Hoffman, 1991; Ross et al., 1992)).

PAGE 14

14 Figure 1-1. Simplified geologic map modified from Mueller, et al., (2005) of the study area with generalized sample locations. The inset shows the study area (dot ted box) in relation to the 0.706 Sr line (dashed line) of Kistler and Peterman (1973).

PAGE 15

15 CHAPTER 2 METHODS Sampling Strategy Sampling of Phanerozoic plutons was conduc ted in two areas of known or suspected Proterozoic crust (Figure 1-1) An eastern group was collected from units near the Paleoproterozoic crust in the Little Belt Mounta ins and within the general confines of the Montana alkali province (MAP). This group contai ns three samples from the Castle Mountains, three samples from the Crazy Mountains, two samp les from the Little Belt Mountains, and one sample from the Big Belt Range. The western group comes from an area of suspected mixed Archean and Proterozoic crust in the western GFTZ (e.g., Muelle r et al., 1996; Foster et al., 2006). Samples were collected in the Flint Creek Range, the Highland Mountains, and the Pioneer Mountains. Due to the exposure of well documented Archean lithologies within the Beartooth Mountains, a sample, (B T 03), was collected to provide an Archean reference and to add Hf isotopic data to the Beartooth geochemical database. Geochemical Preparation Rock samples were crushed using a steel jaw crusher and then ground using a tungsten carbide ball mill to generate homogeneous fine powders for geochemical analysis. Whole rock major element data were obtained via XRF analysis (at the Northern Ontari o Division of Mines). All other geochemical analyses were conducted at the University of Florida. Trace element data were collected after the whole rock powders were dissolved using a HF-HNO3 mixture and analyzed using the Element-2 ICP-MS calibrate d using the following standards: ENDV, QLO-1, BCR-2, AGV-1, RGM-1, and G-2. Sm-Nd, Rb-Sr, and Pb were separated from whole rock samples using standard column chemistry met hods (e.g., Heatherington et al., 1991). Rb-Sr and Sm-Nd spikes were added prior to dissolution in order to determine the elemental concentrations.

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16 Rb-Sr, Sm-Nd, and Pb isotopic compositions we re measured on a Nu-Plasma MC-ICP-MS. Isotopic Sr ratios were acquired in sta tic mode using 5 Faraday collectors and 87Sr/86Sr was corrected for mass-bias us ing the exponential law and 86Sr/88Sr=0.1194. All analyses were done using on-peak measured zeros in order to correct for isobaric interferences from the presence of impurities of Kr in the Ar gas. The data are reported relative to a NBS 987 value of 87Sr/86Sr=0.71025 (+/-0.00003, 2 ), which is applicable to all samples. Nd isotopic measurements were conducted in st atic mode acquiring simultaneously 142Nd on low-2, 143Nd on low-1, 144Nd on Axial, 145Nd on high-1, 146Nd on high-2, 147Sm on high-3, 148Nd on high-4, and 150Nd on high-5 Faraday detectors. The measured 144Nd, 148Nd, and 150Nd beams were corrected for isobaric interference from Sm using 147Sm/144Sm = 4.88, 147Sm/148Sm = 1.33, and 147Sm/150Sm = 2.03. All measured ratios were normalized to 146Nd/144Nd = 0.7219 using an exponential law for mass-bias correction. The data are reported relative to a JNdi-1 value of 143Nd/144Nd=0.512099 (+/-0.000018, 2 ), which is applicable to all samples. Pb isotopic analyses were also conducted on the Nu-P lasma MC-ICP-MS using the Tl normalization technique (Kamenov et al., 2004). The Pb isotop ic compositions are reported relative to the following NBS 981 values: 206Pb/204Pb=16.937 (+/-0.004, 2 ), 207Pb/204Pb=15.491 (+/-0.004, 2 ), 208Pb/204Pb=36.695 (+/-0.009, 2 ), and are applicable to all samples. Mineral Separation Samples were pulverized in a jaw crusher and ground in a disc mill to ensure the disaggregation of rock fragments. The pulverize d material was then sieved to separate the fraction greater than 250 m. The <250m materi al was then passed across the Gemini water table to generate a heavy mineral separate. H eavy mineral separates were then processed using tetrabromoethane (TBE) and met hylene iodine (MI). The density separates received further treatment via magnetic separation on a Frantz isodynamic mineral separator at 1 A electrical

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17 current with progressive reducti on of inclination from +6 degr ees down to +1 degree, depending on the individual sample. The separates were then hand picked to isolate representative zircon grains (Figure 2-1). The zircon grains were mounted in epoxy plugs to facilitate LA-ICP-MS analysis. A zircon standard, FC-1 separated from the Duluth gabbro was also mounted together with the sample zircons (Mueller et al., 2007). Zircon Analysis Zircon grains mounted in epoxy plugs were an alyzed via laser ablation (LA) (Merchantek UP-213 with Supercell) connect ed to the Nu-Plasma MC-ICPMS. Prior to ablation, the grains were subjected to cat hode luminescence imaging by D. Henry at Louisiana State University to identify any zonation or other heter ogeneities. The plugs we re then inserted into the laser ablation chamber and viewed using an internal video camera system. Ablation proceeded in a pattern, ablating the standard FC -1, several sample grains, then the standard again. For both standards and samples, ion beam s were simultaneously collected for Lu, Hf, and Yb following methods in Mueller et al. (2007). Th e reported Hf isotope da ta are relative to the following values of the FC-1 standard: 176Hf/177Hf=0.282168 (+/-0.000026, 2 n=155), and is applicable to all samples. In order to verify the LA protocol one of the zircon samples were dissolved in HF-HNO3 using Teflon-lined bombs under highpressure and temperature and Hf was separated from the REE elements following a method described in Coyne r et al. (2004). Hf isotopes were also measured on the Nu-Plasma MC-ICP-MS via wet plasma to confirm results from the LA method (Table 2-1).

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18 Table 2-1. Individua l zircon analyses Sample 176Lu/177Hf 176Hf/177Hf cor. eHf eHfinitial T(DM) Crazy Mtns. CZ03-01 0.00111507 0.282314 -16.20 -15.14 1.30 CZ03-04 0.00121782 0.282366 -14.36 -13.31 1.23 CZ03-08 0.00094786 0.282312 -16.27 -15.21 1.30 CZ03-05 0.00114934 0.282290 -17.05 -15.99 1.33 CZ03-14 0.00095221 0.282314 -16.20 -15.14 1.29 CZ03-16 0.00059549 0.282332 -15.56 -14.49 1.26 CZ03-18 0.00099166 0.282313 -16.23 -15.17 1.30 CZ03-23 0.00103352 0.282295 -16.87 -15.81 1.32 CZ03-25 0.00093085 0.282311 -16.30 -15.24 1.30 CZ03-27 0.00071784 0.282279 -17.43 -16.36 1.33 CZ03-37 0.00126385 0.282335 -15.45 -14.40 1.28 CZ03-70 0.00111009 0.282388 -13.58 -12.52 1.20 Mean 0.00100213 0.282321 -15.96 -14.90 1.29 Min 0.00059549 0.282279 -17.43 -16.36 1.20 Max 0.00126385 0.282388 -13.58 -12.52 1.33 Crazy Mtns. CZ04-74 0.00307948 0.282328 -15.70 -14.71 1.35 CZ04-71 0.00228082 0.282383 -13.76 -12.74 1.24 CZ04-69 0.00261500 0.282362 -14.50 -13.49 1.28 CZ04-60 0.00347784 0.282215 -19.70 -18.72 1.53 CZ04-61 0.00161267 0.282379 -13.90 -12.86 1.22 CZ04-59 0.00277820 0.282316 -16.13 -15.12 1.36 CZ04-56 0.00116242 0.282296 -16.83 -15.78 1.33 CZ04-57 0.00184098 0.282335 -15.45 -14.42 1.30 CZ04-57 0.00184098 0.282335 -15.45 -14.42 1.30 CZ04-54 0.00170567 0.282327 -15.74 -14.70 1.30 CZ04-54 0.00321592 0.282374 -14.07 -13.09 1.29 CZ04-50 0.00267167 0.282351 -14.89 -13.88 1.30 CZ04-45 0.00303747 0.282304 -16.55 -15.56 1.38 CZ04-41 0.00308721 0.282270 -17.75 -16.76 1.44 CZ04-38 0.00212818 0.282285 -17.22 -16.20 1.38 CZ04-31 0.00069923 0.282307 -16.44 -15.37 1.30 CZ04-12 0.00188463 0.282305 -16.52 -15.48 1.34 CZ04-02 0.00235211 0.282328 -15.70 -14.68 1.32 CZ04-01 0.00151271 0.282347 -15.03 -13.98 1.27 Mean 0.00226610 0.282320 -15.98 -14.96 1.33 Min 0.00069923 0.282215 -19.70 -18.72 1.22 Max 0.00347784 0.282383 -13.76 -12.74 1.53 Multiple Zircons Dissolved CZ04 (Disolved grains) 0.00000218 0.282332 -15.56 -14.01 CZ04 (Disolved grains) 0.00000354 0.282345 -15.10 -14.47 1.22 CZ04 (Disolved grains) 0.00000376 0.282345 -15.10 -14.01 1.22 Mean 0.00000365 0.282345 -15.10 -14.16 1.22

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19 Table 2-1. Continued. Sample 176Lu/177Hf 176Hf/177Hf cor. eHf eHfinitial T(DM) Crazy Mtns. CZ05-01 0.00049381 0.282298 -16.76 -15.68 1.30 CZ05-02 0.00031701 0.282286 -17.19 -16.10 1.31 CZ05-07 0.00265842 0.282371 -14.18 -13.17 1.27 CZ05-10 0.00043758 0.282315 -16.16 -15.08 1.28 CZ05-11 0.00106780 0.282287 -17.15 -16.09 1.34 CZ05-18 0.00037842 0.282234 -19.03 -17.94 1.39 CZ05-22 0.00148518 0.282254 -18.32 -17.27 1.40 CZ05-21 0.00174578 0.282255 -18.28 -17.25 1.41 CZ05-26 0.00042284 0.282296 -16.83 -15.75 1.30 CZ05-28 0.00107653 0.282293 -16.94 -15.88 1.33 CZ05-30 0.00046464 0.282287 -17.15 -16.07 1.32 CZ05-31 0.00124491 0.282249 -18.50 -17.44 1.40 CZ05-35 0.00059057 0.282293 -16.94 -15.86 1.31 CZ05-36 0.00097469 0.282284 -17.26 -16.20 1.34 CZ05-37 0.00095135 0.282290 -17.05 -15.98 1.33 CZ05-42 0.00051158 0.282365 -14.39 -13.32 1.21 CZ05-44 0.00120777 0.282285 -17.22 -16.17 1.34 CZ05-45 0.00042337 0.282303 -16.59 -15.50 1.29 CZ05-51 0.00058866 0.282309 -16.37 -15.30 1.29 CZ05-57 0.00123275 0.282334 -15.49 -14.01 1.28 Mean 0.00091368 0.282294 -16.89 -15.80 1.32 Min 0.00031701 0.282234 -19.03 -17.94 1.21 Max 0.00265842 0.282371 -14.18 -13.17 1.41 Sample 176Lu/177Hf 176Hf/177Hf cor. eHf eHfinitial T(DM) Highland Mtns. HM02-01A 0.00247796 0.281815 -33.84 -32.43 2.07 HM02-01B 0.00087344 0.281141 -57.68 -56.19 2.90 HM02-04 0.00052546 0.281223 -54.78 -53.28 2.77 HM02-09 0.00061265 0.281203 -55.49 -53.99 2.80 HM02-12 0.00061081 0.281932 -29.71 -28.20 1.81 HM02-12B 0.00057584 0.281996 -27.44 -25.94 1.72 HM02-17 0.00065839 0.281788 -34.80 -33.30 2.01 HM02-21 0.00078408 0.281163 -56.90 -55.41 2.87 HM02-22 0.00064186 0.281878 -31.62 -30.11 1.88 HM02-23 0.00103095 0.281148 -57.43 -55.95 2.90 HM02-28 0.00203401 0.281835 -33.14 -31.70 2.02 HM02-28 0.00203401 0.281835 -33.14 -31.70 2.02 HM02-29 0.00030520 0.281145 -57.54 -56.02 2.85 HM02-30 0.00080678 0.281899 -30.87 -29.38 1.86 HM02-60 0.00136552 0.281863 -32.15 -30.68 1.94 HM02-36 0.00112133 0.281799 -34.41 -32.93 2.02 HM02-39 0.00067533 0.281994 -27.51 -26.01 1.73

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20 Table 2-1. Continued. Sample 176Lu/177Hf 176Hf/177Hf cor. eHf eHfinitial T(DM) HM02-44 0.00082564 0.281857 -32.36 -30.87 1.92 HM02-54 0.00081770 0.282328 -15.70 -14.21 1.27 HM02-40 0.00124004 0.281913 -30.38 -28.90 1.87 HM02-42 0.00080258 0.281956 -28.86 -27.36 1.78 HM02-48 0.00122224 0.281925 -29.95 -28.48 1.85 HM02-53 0.00088252 0.281837 -33.07 -31.58 1.95 HM02-05 0.00106174 0.281951 -29.03 -27.55 1.80 HM02-08 0.00103851 0.281987 -27.76 -26.28 1.75 HM02-13 0.00074850 0.281998 -27.37 -25.88 1.72 HM02-14 0.00071329 0.281942 -29.35 -27.85 1.80 HM02-16 0.00115552 0.281252 -53.75 -52.28 2.77 HM02-24 0.00074165 0.281918 -30.20 -28.70 1.83 HM02-03 0.00073105 0.281952 -29.00 -27.50 1.79 HM02-34 0.00079599 0.281897 -30.94 -29.45 1.87 Mean 0.00096486 0.281754 -36.01 -34.52 2.07 min 0.00030520 0.281141 -57.68 -56.19 1.27 Max 0.00247796 0.282328 -15.70 -14.21 2.90 Beartooth Mtns. BT03-01 0.00101299 0.280953 -64.33 -63.06 3.17 BT03-08 0.00025065 0.280888 -66.63 -65.33 3.19 BT03-13 0.00146777 0.280916 -65.64 -64.39 3.26 BT03-17 0.00049562 0.280934 -65.00 -63.71 3.15 BT03-19 0.00075066 0.280912 -65.78 -64.50 3.20 BT03-21 0.00099006 0.280968 -63.80 -62.32 3.14 BT03-26 0.00031389 0.280920 -65.49 -63.98 3.15 BT03-29 0.00024486 0.280919 -65.53 -64.02 3.15 BT03-30 0.00070911 0.280902 -66.13 -64.64 3.21 BT03-32 0.00045113 0.280948 -64.50 -63.00 3.13 BT03-30 0.00053484 0.280942 -64.72 -63.22 3.14 BT03-34 0.00083451 0.280906 -65.99 -64.50 3.22 BT03-42 0.00040308 0.280912 -65.78 -64.27 3.17 BT03-52A 0.00143219 0.280957 -64.19 -62.73 3.20 BT03-53 0.00116798 0.280926 -65.28 -63.81 3.22 Mean 0.00073729 0.280927 -65.25 -63.83 3.18 Min 0.00024486 0.280888 -66.63 -65.33 3.13 Max 0.00146777 0.280968 -63.80 -62.32 3.26

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21 Figure 2-1. CL image of typica l zircon grains from the Highl and Mountains (HM 02) showing igneous zoning.

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22 CHAPTER 3 RESULTS Major Elements Major element data (Table 3-1) show that samples have SiO2 weight percent contents between 55 and 73. Based on normative mineralogy this sample set includes monzogabbro to syenite (Figures 3-1, 3-2). Es timated modal mineralogy and pe trographic analysis, however, suggest the samples are more accurately describe d as granite to monzogranite. The modes were not determined quantitatively thr ough point count analys is. The samples are best classified as granitoids, with the exception of sample CZ 05 fr om the Crazy Mountains. This sample contains no quartz and is best described as an amphibole-plagioclase cumula te (Table 3-2). Due to its anomalous major elemental chemistry, it will be excluded from any further discussion of major and trace elements. It is also important to not e that sample BT03, from the Beartooth Mountains, is an Archean basement sample, not a Mesozo ic plutonic sample. The Flint Creek pluton, (samples FC 01 and FC 02), is more specifically described and mapped as granodiorite by Lewis, (1998). The samples collected from the Highl and Mountains are from units described and mapped by Ruppel et al., (1993). Highland Mo untain sample HM01 is described as a monzogranite and HM02 is described as a granodiori te. The extent of alte ration (Table 3-2) is determined based on a qualitative assessment, primarily on the extent of seritization of plagioclase. With the exception of BT 03, and two sample s from the Crazy Mountains (CZ 03 and CZ 05), the eastern locations are more enriched in total alkalis (Na2O+K2O), ranging from 8 to 10%, than their western, more calc-alkaline counterparts, that range from 6 to 8% (Figure 3-2). This overall trend correlates well with published data, (i.e., the eastern group lies largely within the Montana alkali province (MAP) and the western gr oup lies within the slightly older, calc-

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23 alkaline magmatic province of the Cordilleran orogenic belt. It is worth noting that the Al2O3 contents are low enough that muscovite is not present in any of the sample set. This implies that the samples are likely to be classified as I-type granitoids (C happell and White, 1974). Trace Elements Trace element data are presented in Table 1 and plotted normalized to the composition of N-MORB using values of Sun and McDonough (1989) (Figure 3-3). The normalized data show clear depletion in high field strength elemen ts (HFSE) such as Nb, Zr, and Hf, a positive anomaly in Pb concentrations, and no obvious Eu anomalies. All samples have LREE-enriched rare earth patterns exceeding 100x chondrites (Figure 3-4). None of the samples show strong depletions in HREE (<10x chondrites) that would be expected for melts equ ilibrated with garnet. (La/Yb)N ratios are enriched in the east, with samples ranging from 13.45 to 66.68 with an average of 32.45 whereas the western samples ha ve a much more restricted range of 7.75 to 14.71 with a mean of 12.25, suggesting a more hom ogeneous source and/or set of petrogenetic processes. Overall, the eastern samples are more enriched in the highly incompatible elements such as Ce, Pb, Y, and Nb. For example, there is a geographic contrast in Y+Nb contents, with the easternmost samples ranging from 18 to 100, with an average of 57 and the western samples have much lower, more limited range of concentr ations ranging from 29 to 39 with an average of 35, which reflects the general compositional contra sts between the more alkaline MAP suites and the more calc-alkaline rocks of the western group. Isotopes The Sr, Nd, and Pb isotopic data are presen ted in Table 3-3. The amphibole-plagioclase cumulate (CZ 05) is included in the isotopic disc ussion due to its isotop ic similarity to the granitoids, i.e., its cumulate nature only aff ects its elemental composition. The initial values were calculated using an averag e age estimate of 70 Ma for the western samples and 50 Ma for

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24 the eastern, MAP samples (Dudas et al., 1987; Ha rlan et al., 1988). The range of calculated initial 87Sr/86Sr is 0.7053 to 0.7101, with an average of 0.7068. The range of initial strontium isotopic compositions is greater in the western portion of the study area (0.7056 to 0.7101) compared to the eastern study area (0.7053 to 0.7077). The difference is likely due to, the presence of Archean crust in the western area. Present day 144Nd/143Nd ratios range from 0.5113 81 to 0.5121219, and correspond to Nd values of -24.52 to -8.17 and TDM (depleted mantle model age) of 1.97 to 1.1 Ga respectively. The western portion of the study area typically has more restricted Nd values ranging from 18.2 to -15.0 and TDM of 1.94 to 1.5 Ga compared to the wide range of -24.5 to -8.2 and TDM ages of 1.97 to 1.1 Ga observed in the eastern group. On the 87Sr/86Sr and Nd correlation diagram shown in Figure 3-5, the data plot in th e lower right quadrant. The Archean basement sample from the Beartooth Mountains, calcula ted for 50 Ma, is provided for reference. Whole rock Pb isotopic compositions show a range of values, i.e., 206Pb/204Pb varies from 15.68 to 18.82, 207Pb/204Pb from 15.22 to 15.63, and 208Pb/204Pb from 36.44 to 38.86. These data form a well correlated linear array on a 207Pb/204Pb vs. 206Pb/204Pb diagram that corresponds to an age of 2082 160 Ma calculated with Isoplot (L udwig, 2003) (Figure 3-6). This array includes samples from both geographic and geochemical gr oups and, in particular, samples that contain Pb elemental abundances ranging from 11.9 to 111.9 ppm (Table 2-1). Zircons Hafnium isotopic compositions of individual zirc on grains are presented in Table 3-3. At least twenty grains from selected sample s were analyzed and their model ages (TDM) are summarized in Figure 9. The mean 176Hf/177Hf ratio of 20 grains from CZ 04 is 0.282320 (+/0.000080, 2 ), which corresponds to an epsi lon Hf value of -16.0 and a TDM of 1.3 Ga. The mean 176/177Hf ratio for three analyses of the dissol ved grains from this sample is 0.282345 (+/-

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25 0.000015, 2 ), which corresponds to an epsi lon Hf value of -15.3 and a TDM of 1.2 Ga (Table 21). The similarity of the Hf and TDM values suggests that both methods produced consistent results. The advantage of using the in-situ laser ablation technique is that it allows for numerous grains to be assessed individually, providing multip le model ages for a single whole rock sample, thereby yielding better resoluti on of magmatic and source heter ogeneity compared to a single whole-rock measurement. Laser ablation analys es of zircon were conducted on five samples: HM 02 from the Highland Mountains in the western portion of the study area, CZ 03, 04, 05 from the Crazy Mountains in the eastern portion of the study area, and BT03 from the Beartooth Mountains, the known Archean basement sample The following summarizes the average Hf for the Crazy Mountains sites analyzed: 16.0 (CZ03), -16.0 (CZ04), and -16.9 (CZ05) with ranges from -17.4 to -13.6 (CZ03), -19.7 to 13.8 (CZ04), and -19.0 to -14.2 (CZ05). The Highland Mountains reveal more variability, with an average Hf of -36.0 and a range from -57.7 to -15.7. This wide range includes two distin ct model age populations : ~1.9 Ga and ~2.8 Ga, suggestive of a degree of Archean magmatic inhe ritance in this sample (Figure 3-7). The Archean basement sample (BT 03) yielded an average Hf of -65.3, with values falling between 66.6 to -63.8. These values are clearly far more negative than the values observe in the plutonic zircons

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26Table 3-1. Whole-rock elemental data Major Elements weight percent (XRF) BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 CA03 BT03 HM01 HM02 PM01 FC01 FC02 SiO2 68.09 69.16 62.44 56.14 58.94 47.02 73.75 67.54 66.56 58.86 67.11 70.02 63.81 62.29 55.26 Al2O3 17.10 14.68 16.25 15.00 17.27 17.02 13.58 15.21 15.12 16.18 15.98 15.18 16.75 16.45 15.74 Fe2O3 T 2.26 2.39 4.98 7.74 7.03 12.03 1.67 2.56 3.47 6.46 4.08 2.74 4.85 6.32 8.42 MgO 0.46 0.82 1.88 6.42 2.46 6.67 0.35 1.28 1.96 4.22 1.65 1.08 2.18 2.56 3.98 CaO 2.17 1.43 3.34 6.78 4.24 9.57 0.80 1.89 2.84 6.40 3.60 2.94 4.36 4.82 5.84 Na2O 5.85 4.25 4.49 3.46 4.92 3.19 3.78 5.14 4.42 3.62 3.22 3.49 3.47 3.26 3.42 K2O 3.59 4.38 4.96 2.18 3.31 1.14 4.79 3.42 3.78 2.28 4.42 4.04 3.11 3.04 3.20 TiO2 -0.05 0.56 1.02 0.99 2.48 0.20 0.04 0.26 0.36 0.33 0.12 0.40 0.48 0.87 MnO 0.06 0.06 0.10 0.11 0.10 0.10 0.03 0.02 0.04 0.11 0.08 0.06 0.08 0.09 0.13 P2O5 0.08 0.19 0.51 0.29 0.44 1.02 0.06 0.16 0.24 0.27 0.20 0.12 0.17 0.24 0.62 LOI 0.29 1.64 0.54 0.64 0.27 0.52 1.43 2.61 1.18 0.91 0.44 0.50 0.67 0.72 1.95 TOTAL 99.92 99.05 100.04 99.80 99.98 100.75 100.43 99.88 99.89 99.68 101.10 100.32 99.85 100.27 99.44 Trace Elements ppm (Element 2ICP-MS) BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 CA03 BT03 HM01 HM02 PM01 FC01 FC02 P 881.40 1755.39 4161.43 2613.96 3722.66 8848.78 816.36 1357.63 2121.94 2418.86 1817.13 1256.15 1587.27 2042.50 6319.86 Sc 3.34 3.44 7.58 18.89 9.10 30.78 5.14 5.18 7.29 15.74 9.11 5.90 10.27 12.45 21.20 V 51.71 31.70 79.79 139.33 93.93 322.26 15.13 34.01 56.91 97.92 75.22 38.88 79.97 107.91 297.94 Cr 5.10 10.51 17.57 316.90 12.65 117.26 4.45 31.85 59.63 138.57 10.58 17.20 25.86 13.62 74.21 Mn 598.84 547.99 982.47 1074.24 979.98 981.06 380.70 180.91 434.73 1116.56 702.04 618.83 757.15 904.61 1481.08 Co 22.57 25.86 27.15 35.99 24.10 37.32 96.35 18.90 24.24 32.15 21.03 31.66 23.74 24.46 24.99 Ni 3.83 6.37 10.87 105.09 11.14 96.51 6.71 19.68 28.93 60.93 7.44 10.02 9.54 6.20 46.12 Cu 6.32 4.57 16.88 16.23 17.52 50.17 5.64 14.99 25.36 23.00 7.51 26.70 8.58 6.42 148.92 Zn 38.24 106.24 99.34 76.58 73.50 77.09 79.74 106.10 118.82 72.70 38.68 61.90 70.01 46.80 99.91 Ga 21.37 17.93 20.04 17.83 20.22 22.96 22.60 17.18 19.21 17.07 15.77 14.42 19.07 18.44 22.52 Rb 137.70 154.98 181.02 53.47 66.73 20.02 732.45 53.01 95.66 63.85 116.95 174.52 99.97 91.25 92.43 Sr 1278.26 838.51 901.50 867.21 895.30 1549.85 189.38 579.96 668.98 513.41 531.85 595.48 457.12 576.12 872.96

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27Table 3-1. Continued. BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 CA03 BT03 HM01 HM02 PM01 FC01 FC02 Y 15.29 14.32 20.78 21.95 21.79 24.43 34.50 10.89 14.51 21.39 23.85 20.99 21.47 21.41 29.09 Zr 84.12 144.86 106.47 97.67 148.35 70.87 137.17 109.45 181.89 126.38 72.75 83.65 64.30 51.47 129.10 Nb 22.80 61.26 79.90 22.27 38.55 17.51 62.89 7.53 20.46 7.64 15.09 16.97 11.98 10.95 8.27 Ba 1692.40 1952.73 2273.60 1116.41 1761.62 783.55 597.88 2005.46 2363.99 1279.19 1036.84 1214.83 1297.30 1258.18 1033.94 La 34.15 77.97 90.53 44.57 53.78 37.47 107.87 32.46 67.93 35.40 35.96 36.28 33.36 32.87 29.12 Ce 51.60 134.25 161.62 83.18 96.21 77.63 129.04 44.99 107.62 74.21 67.81 64.33 61.43 63.89 56.80 Pr 5.07 11.62 15.32 8.66 9.59 9.55 14.15 5.66 10.12 8.91 7.31 6.78 6.55 7.07 6.49 Nd 18.99 39.26 54.13 33.13 35.86 43.01 45.42 21.04 34.96 35.96 27.61 25.48 25.25 28.12 27.15 Sm 3.34 5.21 7.72 5.72 6.00 8.21 7.15 3.31 4.89 6.21 4.97 4.51 4.64 5.07 5.48 Eu 1.05 1.33 1.98 1.60 1.76 2.41 1.07 0.99 1.42 1.65 1.17 1.12 1.22 1.37 1.65 Gd 3.08 4.40 7.09 5.10 5.41 7.02 6.24 2.72 4.76 5.22 4.51 4.15 4.27 4.61 5.30 Tb 0.43 0.51 0.78 0.70 0.73 0.96 0.92 0.36 0.53 0.67 0.65 0.60 0.61 0.62 0.78 Dy 2.36 2.36 3.47 3.61 3.56 4.84 5.04 1.59 2.22 3.43 3.56 3.36 3.29 3.29 4.55 Ho 0.47 0.42 0.64 0.69 0.64 0.91 1.04 0.26 0.36 0.66 0.72 0.69 0.65 0.64 0.96 Er 1.19 0.99 1.83 1.87 1.57 2.19 2.99 0.61 0.93 1.84 2.03 1.84 1.74 1.74 2.65 Tm 0.23 0.21 0.29 0.31 0.31 0.32 0.48 0.17 0.21 0.30 0.36 0.34 0.31 0.30 0.42 Yb 1.32 0.96 1.54 1.72 1.41 1.72 3.35 0.58 0.73 1.73 2.21 2.10 1.78 1.75 2.70 Lu 0.21 0.15 0.23 0.27 0.23 0.24 0.51 0.10 0.13 0.27 0.33 0.34 0.26 0.27 0.41 Hf 2.34 3.82 3.09 2.91 3.99 2.15 4.99 3.17 4.78 3.48 2.28 2.63 1.79 1.60 3.46 Ta 3.61 4.93 6.26 2.19 3.84 1.60 18.42 2.68 2.66 1.72 2.99 4.18 2.66 2.08 0.85 Pb 22.24 119.02 48.44 17.23 17.25 11.92 45.23 22.93 25.91 17.60 16.88 18.76 15.43 8.94 14.66 Th 9.24 51.17 32.20 9.52 11.09 4.41 49.31 7.55 17.97 14.95 17.94 19.96 10.14 8.83 6.38 U 2.99 6.88 4.65 2.08 2.31 0.98 3.93 2.29 2.74 1.94 2.57 2.22 2.29 2.63 1.30 La/Lu 164.46 524.81 388.51 167.75 237.61 156.13 210.65 309.73 521.20 133.33 108.75 107.84 126.99 120.78 71.67 La/Yb 1.10 2.52 2.92 1.44 1.73 1.21 3.48 1.05 2.19 1.14 1.16 1.17 1.08 1.06 0.94

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28Table 3-2. Sample descriptions Sample Mountain Range Rock Type based on Estimated Modal Mineral Assemblages Latitude Longitude BB01 Big Belt Mts Granitoid Plag, qtz, k-spar, amph 46.460 111.248 W LB01 Little Belt Mts. Granitoid K-spar, plag, qtz 46.964 110.756 W LB02 Little Belt Mts. Granitoid Plag, k-spar, qtz, amph, bt 47.076 110.637 W CZ03 Crazy Mts. Granitoid Plag, amph, qtz 46.042 110.289 W CZ04 Crazy Mts. Granitoid Plag, qtz, bt 46.042 110.289 W CZ05 Crazy Mts. Amphibole-Plagioclase Cumulate Plag, amph, bt 46.040 110.274 W CA01 Castle Mts. Granitoid Plag, k-spar, qtz, bt 46.456 110.685 W CA02 Castle Mts. Granitoid K-spar, plag, qtz 46.447 110.682 W CA03 Castle Mts. Granitoid Plag, qtz, k-spar, amph 46.424 110.589 W BT03 Beartooth Mts Granitoid (Archean Basement) Plag, k-spar, qtz, amph, bt 45.008 109.521 W HM01 Highland Mts. Granitoid (Monzogranite, Ruppel et al., 1993) Plag, k-spar, qtz, bt, amph 45.870 112.449 W HM02 Highland Mts. Granitoid (Granodiorite, Ruppel et al., 1993) Qtz, plag, k-spar, bt 45.833 112.361 W PM01 Pioneer Mts. Granitoid Plag, qtz, k-par, bt, amph 45.820 113.273 W FC01 Flint Creek Mts. Granitoid (Granodiorite/granite, Lewis, 1998) Plag, qtz, k-spar, bt, amph 46.315 113.251 W FC02 Flint Creek Mts. Granitoid (Quartz monzonite, Lewis, 1998) Plag, k-spar, qtz, amph, bt, pyr Sample Mountain Range Rock Type based on CIPW Normative Mineral Assemblages A-P-Q Mineral Assemblages Alteration BB01 Big Belt Mts Syenite K-spar, qtz, plag Ab, Or, Qz, An, Hy, Mt, Di, Ap little-none LB01 Little Belt Mts. Granite/syenogranite K-spar, qtz, plag Ab, Or, Qz, An, Hy, Co, Mt, Ap, Il little-none LB02 Little Belt Mts. Alkali-feldspar sy enite Qtz., k-spar, plag Ab, Or, An Hy, Qz, Di, Il, Mt, Ap little-none CZ03 Crazy Mts. Monzogabbro Plag, k-spar, qtz Ab, Hy, An, Or, Di, Qz, Il, Mt, Ap little-none CZ04 Crazy Mts. Monzonite Plag, k-spar, qtz Ab Or, An, Hy, Qz, Di, Il, Mt, Ap little-none CZ05 Crazy Mts. Alkali-feldspar syenite Plag, Kspar, ol An, Ab, Ol, Di, Or, Il, Mt, Ap none CA01 Castle Mts. Alkali-feldspar granite K-spar, Qtz, Plag Ab, Qz, Or, An, Hy, Co moderate CA02 Castle Mts. Quartz syenite K-spar, Qtz, Plag Ab, Or, Qz, An, Hy, Mt, Ap, Il moderate CA03 Castle Mts. Quartz monzonite Plag, k-spar, qtz Ab, Or, Qz, An, Hy, Di, Mt, Ap, Il litte-moderate BT03 Beartooth Mts Monzogabbro Plag, k-spar, qtz Ab, An Hy, Or, Qz, Di, Mt, Il, Ap litte-moderate HM01 Highland Mts. Alkali-feldspar granite Plag, qtz, k-spar Ab, O, Qz, An, Hy, Mt, Il little-none HM02 Highland Mts. Alkali-feldspar granite Plag, qt z, k-spar Ab, Qz, Or, An, Hy, Mt little-none PM01 Pioneer Mts. Quartz monzodiorite Plag, k-spar qtz Ab, An, Or, Qz, Hy, Mt, Il, Ap, Co none FC01 Flint Creek Mts. Alkali-feldspar quartz syenite K-spar, qtz, plag Ab, An, Or, Qz, Hy, Di, Mt, Il, Ap little-none FC02 Flint Creek Mts. Alkali-feldspar sy enite Plag, k-spar, qtz Ab, Or, An, Hy, Di, Qz, Mt, Il, Ap moderate

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29 Table 3-3. Whole rock isotopic data BB01 LB01 LB02 CZ03 CZ04 CZ05 CA01 CA02 87Sr/86Sr 0.706476 0.707633 0.706713 0.706042 0.705567 0.706065 0.708586 0.707956 87Sr/86Srinitial 0.706350 0.706966 0.706106 0.705918 0.705331 0.706024 0.705625 0.707677 87Rb/86Sr 0.129685 0.686737 0.625005 0.127486 0.242982 0.042316 3.051352 0.287715 Sr ppm 1651.88 570.15 794.96 823.49 805.57 1228.19 110.26 507.86 Rb ppm 74.0359 135.318 171.715 36.2823 67.6478 17.9617 116.245 50.4993 143Nd/144Nd 0.511976 0.511719 0.511891 0.511899 0.511949 0.511911 0.512219 0.511381 143Nd/144Nd inital 0.511943 0.511695 0.511864 0.511865 0.511921 0.511873 0.512187 0.511353 147Sm/144Nd 0.101412 0.072506 0.082080 0.104049 0.084673 0.116912 0.098750 0.084862 Nd -12.91 -17.93 -14.57 -14.42 -13.44 -14.18 -8.17 -24.52 Nd initial -12.307 -17.137 -13.842 -13.826 -12.727 -13.675 -7.59 -23.81 T(DM) 1.45 1.43 1.33 1.59 1.29 1.78 1.10 1.97 Nd ppm 15.1589 41.6829 48.263 29.8258 45.363 35.355 28.11 24.829 Sm ppm 2.542 4.997 6.55 5.1312 6.35104 6.835 4.59 3.4839 208Pb/204Pb 37.92 37.80 37.49 36.92 36.71 36.99 37.16 37.03 207Pb/204Pb 15.50 15.45 15.39 15.35 15.28 15.35 15.38 15.32 206Pb/204Pb 18.07 17.38 16.85 16.41 16.08 16.43 16.77 16.44 CA03 BT03 HM01 HM02 PM01 FC01 FC02 87Sr/86Sr 0.706312 0.713812 0.707713 0.707345 0.711666 0.709967 0.705934 87Sr/86Srinitial 0.705846 0.713575 0.707132 0.706788 0.710057 0.709441 0.705606 87Rb/86Sr 0.480585 0.244134 0.598309 0.573704 1.656621 0.541330 0.337581 Sr ppm 467.44 589.10 624.80 513.65 133.10 505.02 515.70 Rb ppm 77.6379 49.7044 129.194 101.843 76.2067 94.4811 60.1665 143Nd/144Nd 0.511579 0.510671 0.511826 0.511708 0.511826 0.511854 0.511869 143Nd/144Nd inital 0.511554 0.511785 0.511657 0.511784 0.511808 0.511813 147Sm/144Nd 0.076819 0.099056 0.090201 0.10218 0.091726 0.101200 0.121629 Nd -20.66 -38.37 -15.84 -18.219 -15.84 -15.29 -15.00 Nd initial -19.896 -14.89 -17.38 -14.91 -14.44 -14.33 T(DM) 1.63 3.20 1.50 1.83 1.52 1.61 1.94 Nd ppm 26.594 38.624 33.813 18.9877 28.821 26.092 19.137 Sm ppm 3.3779 6.326 5.043 3.2079 4.371 4.366 3.849 208Pb/204Pb 36.44 43.18 38.29 37.89 38.86 38.43 38.03 207Pb/204Pb 15.22 16.04 15.55 15.41 15.63 15.59 15.50 206Pb/204Pb 15.68 19.80 17.98 17.02 18.82 18.34 17.70

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30 Figure 3-1. The classification of granitoids based on their molecular normative An-Ab-Or composition after Barker (1979) (heavy lin es) and OConnor (1965) (dotted lines) from Rollinson (1991).

PAGE 31

31 Figure 3-2. Total alkali vs. SiO2, shows the chemical variation within the dataset. Note that the eastern samples are alkaline and the west ern samples are calc-alkaline. The plagioclase-amphibole cumulate from th e Crazy Mountains (CZ 05) has been excluded.

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32 Figure 3-3. Trace element abundance diagra ms, normalized to N-MORB (Sun and McDonough, 1989). The plagioclase-amphibole cumulate from the Crazy Mountains (CZ 05) has been excluded. The depletion in HFSE su ch as Nb indicate that the magmas were likely generated in a convergent margin set ting and/or were derived from an ancient subduction environment.

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33 Figure 3-4. Rare earth element (REE) abundances normalized to chondritic meteorite values (Sun and McDonough, 1989). The plagioclaseamphibole cumulate from the Crazy Mountains (CZ 05) has been excluded. The enrichment in HREE is less than 10x chondrites and suggests a lower crustal source containing garnet, amphibole, and possibly pyroxene. The lack of Eu anomalie s also indicates that the source material was not in equilibrium with plagioclase.

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34 Figure 3-5. Initial 87Sr/86Sr and Nd variation diagram calculated at 50 Ma. for the eastern samples and at 70 Ma. for the western samp les; the value for the Beartooth gneiss sample is calculated at 50 Ma.

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35 Figure 3-6. Whole rock Pb isotopi c plot showing linear array of sample data from eastern and western sample sets. Linearity of the arra y can be interpreted in terms of a common age of ~2.0 Ga for the source of all sample s. The age of the source is essentially the same as the oldest Proterozoic ages of the exposed basement in the Little Belt Mountains (Mueller et al., 2002).

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36 Figure 3-7. Individual zircons from the Crazy (CZ 03-05), the Highland (HM 02) and the Beartooth Mountains (BT 03) were analyzed via La-ICP-MS. The Hf model age (TDM) is compared to the whole rock Nd model age (TDM) shown as a diamond symbol. The bin size is 0.1 Ga a nd spans from 1.0 Ga to 3.4 Ga.

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37 CHAPTER 4 DISCUSSION Major Elements Major element abundances and petrographic anal ysis are essential for rock classification, as well as for providing insight into petrogenesis and source. These rocks exhibit many of the mineralogical and chemical characteristics of I-T ype granites as defined by Chappell and White (1974). Mineralogically, the re lative abundance of amphibole co mpared to biotite and the observed lack of muscovite, support the I-type classifica tion of these samples. S-type granites are characterized by higher mica abundance, especi ally muscovite. I-Type granites also yield abundant magnetite (instead of ilmenite) and pink and white alkali feldsp ars, both of which are present in the sample set. Additionally, the pr esence of mafic enclaves in outcrops in the Big Belt Range, Highland Mountains, an d the Pioneer Mountains indica te a non S-type source. Chemically, these samples also correspond to I-type granites in CaO, Na2O, and Sr concentrations (Table 3-1). The average values of 3.68 weight percent, 4.06 weight percent, and 711 ppm respectively are too high to correspond to S-type granite s (Bowden, 1984). In addition, the CIPW normative mineralogy demonstrates th at the average amount of quartz is below the amounts typically found in S-type rocks, and that the amount of corundum is within the limits (below 1.0) of an I-type granite (Table 3-1). This evidence is compatible with petrogenesis involving a mafic, metaigneous source. Trace Elements Trace element concentrations help provide estimates of the source material composition, the residual minerals left behind by melt extrac tion, and the extent of melt mixing and source variability. The REE patterns in all rocks s how enrichment in LREE and a corresponding less enriched distribution of HREE, characteristic of continental gr anitoids (Pearce, et al., 1984;

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38 Winter, 2001). The enrichments in HREEs are less than 10x chondrites, suggesting a lower crustal source potentially cont aining one or more of the follo wing: garnet, amphibole, and/or pyroxene. Y and Yb, however, are concentrated in garnet, and the lack of any negative Y or Yb anomaly again suggests that the magma source(s) was not garnet-bearing (Figures 3-3 and 3-4). The lack of Eu anomalies indicate that plagiocl ase was absent from the source, that the source had not previously undergone a si gnificant feldspar fractionation cycle (Halliday and Stephens, 1984), and that plagioclase fractionation had very limited impact on magmatic evolution in these samples. This provides further evidence of a man tle and/or lower crust source that lacked an upper crustal history. LILEs (large ion lithophile elements) are also incompatible and behave similarly to the HFSE in solid-melt exchange, but behave differently in the presence of an aqueous fluid. Given that this dataset show s enrichment in Rb, Ba, and Pb, but lesser enrichments in the HFSE, a high LILE/HFSE ratio results (Figure 3-3). The decoupling of these two chemical groups is best explained by the partic ipation of water-rich fl uids in the genesis of subduction zone magmas (e.g., Hanson, 1978; Wint er, 2001). Depletion in HFSEs and Nb in particular indicate that the magm as were likely genera ted in a convergent margin setting, were derived from rocks produced in an ancient subduction environment (Morris and Hart, 1983; Saunders et al., 1991), or some combination of the ancient s ubducted material and the younger Cretaceous/Tertiary subduction. Major and trace element abundances for these inte rmediate granitoids, therefore, strongly suggest that the samples were derived primarily, if not exclusively, from a mafic, meta-igneous, lower crustal source. The stimulus for melting in both the eastern and west ern regions is likely related to Farallon plate subduction, despite the alkalic vs. calc-alkal ic nature of the rocks from the eastern and western groups respectively (Coney & Reynolds, 1977; Humphreys et al., 2003).

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39 An alternate option is that the lo wer crustal source formed in a subduction environment related to the collision between the Wyoming Province and the Medicine Hat Bl ock. This ambiguity of the age of the source and potential mixing of Farallon-derived fluids or magmas derived from an ancient subduction generated mafic lower crust cannot be resolved with trace element data alone. Age of the Lower Crust Regardless of their petrochemical compositi on, contemporaneous intrusions emplaced in similar country-rocks and derived from similar sources can be expected to show very similar SrNd-Pb-Hf isotopic systematics. Measurements of present day isotopic valu es, particularly for Sr, Nd, and Pb, can be used to calcu late the initial isotopic ratios for the source material. These calculated initial values are useful for determin ing both petrogenetic and model age information about the source. Initia l Sr isotopic values range from 0.7050.710, generally compatible with an ancient crustal origin (e.g., Arth et al., 1986, Mu eller, et al., 1997). Figure 3-5 shows initial 87Sr/86Sr and Nd ratios are generally corre lative and the negative Nd values strongly indicate that there was involvement of an older, enriched source. Sm and Nd are far less susceptible to fractionation during melting and subsequent alteration than are Rb and Sr and, as a result, the 143Nd/144Nd ratio can be used to provide a more reliable indicator of the age of the material in the source regi on(s). The range of Sm/Nd model ages generated by these rocks suggests that the source(s) are likely to be both compositionally and chronologically heteroge neous. Although the actual TDM are scattered from 1.1-1.9 Ga, this range is well within the temporal boundaries of th e Proterozoic, indicating that there is not likely to be significant involvement of Ar chean crust. It is important to note that the upper limit of this range corresponds with the oldest basement rock U/Pb zircon age date determined for the Little Belt Mountains at ~1.9 Ga (Mueller et al., 2002) and is therefore unlikely to be a fortuitous mixture of Archean and younger crust.

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40 The heterogeneity seen in the Rb-Sr and Sm-N d systematics is not evident in the Pb-Pb system. A whole rock Pb isotopic plot (Figur e 8) produces a linear a rray that suggests a Paleoproterozoic source. Extensive recent mixi ng to produce a homogenous array for individual plutons over this large of an area seems unlikel y; therefore, mixing a nd establishment of the diverse U/Pb ratios needed to form the array was more likely to have been in the Proterozoic. These whole rock Pb isotopic data, therefore, sugg est that this lower crustal source is likely Proterozoic and that ~2.0 Ga is a reasonable approximation of its age (Figure 3-6). An age of ~2.1 Ga compares favorably with the age of th e oldest Proterozoic rocks in the area (~1.9 Ga; Mueller et al., 2002) and the oldest Sm-Nd model ages. As noted above, the Sm-Nd model ages are not consistently Paleoproterozoic. Some of this variability is likely due to heterogeneities in the source re gion, variable fractionation of Sm and Nd, and/or mixing between sources (Mueller et al., 1995, 1996). Sm-Nd model ages suggest some mixing of the Proterozoic source(s) characteristic of the Pb array with a younger asthenospheric Nd component. The older com ponent may approximate the ~1.9 Ga basement age from the Little Belt Mountains and the ot her may be derived from fluids liberated by Farallon subduction. The primary reason for the difference in response of the Sm-Nd and Pb-Pb systems during petrogenesis of indi vidual rocks is directly related to the smaller differences in the elemental abundances of Sm and Nd compar ed to Pb elemental abundances between the mantle and crust. This differential makes for a more homogeneous, more crust-dominated response of the Pb system than the Sm -Nd system in crustal environments. Further constraints on the age of the source are provided by Lu /Hf isotopic ratios preserved in zircon crystals formed during the crystallizatio n of the granitoid melts or directly inherited from the source. The Lu/Hf system is similar to the Sm/Nd system in providing insight into

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41 petrogenetic and crustal processes, with the advantage of yielding numerous analyses from zircon crystals rather than the averaging repr esented by whole-rock Sm-Nd data. These Hf values provide a snapshot of the isotopic co mposition of the melt (and hence source region) itself and, in some cases, zircons inherited from that source or sources are likely to remain largely undisturbed by incorporation in the melt or subsequent weathering, hydrothermal, or other alteration processes. This effect is observed in the Highland Mountains (sample HM02), where the Nd model age (TDM) is ~1.8 Ga and correlates well with the primary Hf model age (TDM) data, but fails to identify two additional Hf model age populations detected at ~1.4 Ga and ~2.8 Ga (Figure 3-7). Tectonics The geochemical data presented above suggests that the primary component(s) of the lower crust within the GFTZ is Proterozoic, generated as juvenile crust in a convergent setting (e.g., Mueller et al., 2002). The addition of individu al zircon analyses reve al that the Highland Mountains in the western porti on of the study area contain an additional zircon population characterized by an Archean Hf model age. Sa mples in the eastern region do not possess zircons with an Archean signature. Th e zircon Hf data from the Highla nd Mountains seems to indicate the presence of Archean crust at depth mixed with a Paleoproterozoic component. This would suggest that the collision between the Medici ne Hat Block and the Wyoming province was not between parallel margins. Instead, these data support the idea of an oblique convergence along the Medicine Hat and Wyoming Province that produ ced relatively more juvenile crust in the central GFTZ and more reworked Archean crust in the western GFTZ, as suggested by Mueller et al. (2005). This pattern of reworked Archean crust in the Highland Mount ains suggests a point of collision between the Wyoming Province and Me dicine Hat block in this region, reworking slivers of Archean crust into the juvenile crust of the Paleoproterozoic. The absence of this

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42 direct collision in the east is inferred by the presence of only Paleoproterozoic Hf model ages seen in samples from this region. Later convergence in the GFTZ was then accommodated by increasing strike-slip transl ation (Mueller et al, 2005). The argument that the GFTZ is not a collis ional boundary, but inst ead an intracratonic shear zone reactivated during the Trans-Huds on Orogeny (Boerner, 1998), becomes less tenable given the results of this study because shear zone s are not typically characterized by magmatism, particularly the formation of juvenile crust. The geochemical data presented above indicate that active magmatism was occurring during the formati on of the GFTZ in the Paleoproterozoic. The trace elemental data, particularly HFSE depletio n, strongly suggest a convergent margin setting for generation of the present lower crust. The age constraints provided by isotopic model ages strongly suggest that the trac e element signal largely devel oped in the Paleoproterozoic. Understanding the tectonic evolu tion of the GFTZ provides insight into the identity of the conjugate margins of Laurentia in Rodini a paleoreconstructions. SWEAT and AUSWUS reconstructions (Jefferson, 1978; Moores, 1991; Hoffman, 1991; Ross et al., 1992; Burrett and Berry, 2000; Karlstrom et al., 2001) primarily re ly on matching the Proterozoic Yavapai, Mazatzal, and Grenville belts on the southwestern Laurentian margin with similar-age orogenic provinces in Australia or An tarctica. Borg and DePaolo (1994) observed that these reconstructions are dependent on the geochronol ogy and isotopic mapping that defines each of these provinces and suggested a possible role for an Antarctica-Idaho connection. The SWEAT and AUSWUS models are difficult to uniquely test on the basis of these correlations due to the widespread distribution of 1.7-1.0 Ga accretionary and collisional belts. These widespread, similarly aged belts, therefore, are limited in u tility as piercing points for reconstructions. Sears and Price (1978; 2000; 2003) argue for a Siberia-Laurentia connection. Dikes and sills in the

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43 Wyoming Province and Anabar shield of Siberia appear to share similar ages of emplacement at ~1500 Ma (Sears and Price, 2003). The Belt-Pur cell basin shows many si milarities with the Udzha basin of Siberia, as Sears and Price (2003) note the seemingly continuous pattern of sediment transport and provenance. Sears et al. (2004) also note an intriguing correlation between the GFTZ and the Aekit terrane of Sibe ria, which they argue separated during the opening of the Belt-Purcell/Udzha basin. This may provide the first robust target for detailed isotopic mapping on a possible conjugate margin. An isotopic study of the Siberian Aekit terrane would test the validity of this Siberian-Laurentia model. An additional target for detailed isotopic studies is provided by Burrett and Berry (2000) who connect the GFTZ with the Diamantina Lineament located in Australia (i.e. AUSWUS reconstruction). Without such data, however, refined isotopic data from the GFTZ can be used to identify a unique piercing point to better evaluate the conjugates proposed by thes e models. Isotopic studies conducted on the potential conjugate margin(s) will help ev aluate each, as the mix of Archean and Paleoproterozoic crust forming the GFTZ should serve as an excellent diagnostic marker.

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44 CHAPTER 5 CONCLUSIONS Detailed geochemical analyses conducted on Cretaceous-Tertiary gran itic plutons within the GFTZ provide valuable insight into the com position of the lower crust in the GFTZ and its tectonic origin. These plut ons are all I-type granites, de rived from the melting of a predominantly mafic, ancient, lower crustal sour ce(s) that originally formed as the result of subduction. Isotopic data (Sr, Nd, Pb, and Hf) sugge st that the lower crust is Paleoproterozoic in age, indicating that new lower crust was being generated during this time interval, which is conducive to viewing the GFTZ as a collisional suture zone. Th ese characteristics of the GFTZ make it a more important piercing point for, assessing Rodinia reconstruction models.

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45 LIST OF REFERENCES Arth, J.G., Zen, E-an, Sellers, F. and Hammarstrom, J., 1986, High initia l Sr isotopic ratios and evidence for magma mixing in the Pioneer batholith of southwest Montana: Journal of Geology, v. 94, p. 419-430. Barker, F., 1979, Trondhjemite: Definition, environm ent and hypotheses of origin, in, Trondhjemites, dacites, and related rocks: edited by Barker, F., Elsevier Amsterdam, p.1-12 Bennet, V., and DePaolo, D.J., 1987, Proterozoic crustal history of the western United States as determined by neodymium isotopic mapping: Geol ogical Society of Am erica Bulletin, v. 99, p. 674-685. Boerner, D.; Craven, J.; Kurtz, R.; Ross, G.; and Jone s, F. 1998, The Great Falls tectonic zone: Suture or intracontinental shear zon e?: Canadian Journal of Earth Science, v. 35, p. 175. Borg, S.G., and DePaolo, D.J., 1994, Laurentia, Australia, and Anta rctica as a late Proterozoic supercontinent: constraints from is otopic mapping: Geology, v. 22, p. 307-310. Bowden, P, Batchelor, R.A., Chappell, B.W., Didier, J., and Lameyre, J., 1984, Petrological, geochemical, and soure criteria for the classifica tion of granitic rocks: A discussion: Physics of the Earth and Planetary Interiors, no. 35, p 1-11. Burrett, C., and Berry, R., 2000, Prot erozoic Australia-Western United States (AUSWUS) fit between Laurentia and Australi a: Geology, v. 28, p. 103-106. Chappell, B.W., White, A.J.R., 1974, Two contrasting granite t ypes: Pacific Geology, v. 8, p. 173-174. Coney, P.J., and Reynolds, S.J., 1977, Flattening of the Farallon slab: Nature, v. 270, p. 403-406. Coyner, S.J., Kamenov, G.D., Mueller, P.A., Rao, V., Foster, D.A., 2004, FC-1: A zircon reference standard for the determination of Hf isotopi c compositions via laser ablation ICP-MS: Eos Trans., AGU, 85 (47), Fall Meet. Suppl., V51C-0584. Dahl, P. S., Holm, D. K.; Gardner, E. T., Hubach er, F. A., and Foland, K. A., 1999, New constraints on the timing of Early Proterozoic tectonism in th e Black Hills (South Dakota), with implications for docking of the Wyoming province with Laurentia : Geological Society of America Bulletin, v. 111, p. 1335. DePaolo, D.J., 1988, Age dependence of the compositi on of continental crust: Evidence from Nd isotopic variations in granitic rocks: Eart h and Planetary Science Letters, v. 90, p. 263-271. Dickinson, W.R., 1981, Plate tectonics of the continental margin of California, in The Geotectonic Development of California: edite d by W.G. Ernst, Prentice-Hall, Englewood Cliffs, N.J., 706 pp. Duds, F. .; Carlson, R. W.; and Eggler, D. H. 1987, Regional middle Proterozoic enrichment of the subcontinental mantle source of igneous ro cks from central Montan a: Geology, v. 15, p. 22 25.

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46 Farmer, G.L. and DePaolo, D.J., 1983, Origin of Mesozo ic and Tertiary granite in the western United States and implications for pre-Me sozoic crustal structure 1. Nd and Sr isotopic studies in the geocline of the northern Great Basin: Journa l of Geophysical Research, v. 88, no. B4, p. 33793401. Foster, D.A., P.A. Mueller, D.W. Mogk, J.L. Woode n, and J.J. Vogl, 2006, Proter ozoic evolution of the western margin of the Wyoming Craton: Implicati ons for the tectonic and magmatic evolution of the northern Rocky Mountains: Canadian J ournal of Earth Sciences, v. 43, p. 1601-1619. Gallet, Y. and Pavlov, V.E., Semikhatov, M.A ., and Ptrov, P.Y., 2000, Late Mesoproterozoic magnetostratigraphic results from Siberia: Pale ogeographic Implicati ons and magnetic field behaviour: Journal of Geophysical Research, v. 105, p. 16481-16499. Gunn, S.H., 1991, Isotopic Constraint s on the crustal evolution of southwestern Montana. Ph.D. Dissertation, University of California at Santa Cruz, 204pp. Halliday, A.N., and Stephens, W.E., 1984, Crustal contro ls on the genesis of the 400 Ma old Caledonian granites: Physics of Earth and Planetary Interiors, v. 35, p. 89-104. Hanson, G.N., 1978, The application of trace elements to the petrogenesis of igneous rocks of granitic composition: Earth and Planetar y Science Letters, v. 38, p. 26-43. Harlan, S.S., Geissman, J.W., Lageson, D.R., and Snee, L.W., 1988, Paleomagnetic and isotopic dating of thrust belt deformation al ong the eastern edge of the Hele na salient, northern Crazy Mountains, Montana: Geological Soci ety of America Bulletin, v. 100, p. 492-499. Heatherington, A., Mueller, P.A., 1991, Geochemical ev idence for Triassic rifting in southwestern Florida: Tectonophysics, v. 188, p. 291-302. Hoffman, P., 1988, United Plates of America, the bi rth of a craton: Annual Review of Earth and Planetary Science, p. 16543-16603. Hoffman, P.J., 1991, Did the breakout of Laurentia turn Gondwanaland inside-out?: Science, v. 252, p. 1409-1412. Humphreys, E., Hessler, E., Dueker K., Farmer, G.L., Erslev, E. and Atwater, T. 2003, How Laramideage hydration of North American lithosphere by the Farallon slab controlled subsequent activity in the western United States: Intern ational Geology Review, v. 45, p. 575-595. Jefferson, C.W., 1978, Correlation of middle and upper Pr oterozoic strata between northwestern Canada and south and central Australia [abs.]: Geol ogical Association of Canada Program with Abstracts, v. 13, p. 429.

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47 Kamenov, G.D., Mueller, P., and Perfit, M., 2004, Op timization of mixed Pb -Tl solutions for high precision isotopic analyses by MC-ICP-MS: Jour nal of Analytical Atomic Spectrometry, v.19, no. 9, p. 1262-1267. Karlstrom, K.E., Ahall, K.L., Harlan, S.S., W illiams, M.L., McLelland, J., and Geissman, J.W., 2001, Long-lived (1.8-1.0 Ga) convergent or ogen in southern Laurentia, its extensions to Australia and Baltica, and implications for refining Rodi nia: Precambrian Research, v. 111, p. 5-30. Kistler, R.W., and Peterman, Z.E., 1973, Variations in Sr, Rb, K, Na, and initial 87Sr/86Sr in Mesozoic granitic rocks and intruded wall rocks in central California: Geological Society of America Bulletin: v.84, p. 3489-3512. Lewis, R.S., 1998, Geologic map of the Butte 1 x 2 quadrangle, Montana: M ontana Bureau of Mines and Geology Open File MBMG 363. Ludwig, K. R. 2003. Users manual for Isoplot 3.00 (Berkeley Geochronology Center Special Publication 4. Berkeley Geochronology Center. Meert, J.G. and Torsvik, T.H., 2003. The making and unmaking of a supercontinen t: Rodinia Revisited: Tectonophysics, v. 375, p. 261-288. Mogk, D.W., Mueller, P.A., and Wooden, J.L., 1992, The nature of Archean terrane boundaries: An example from the northern Wyoming Provi nce: Precambrian Research, v. 55, p. 155-168. Moores, E.M., 1991, Southwest U.S.East Antarctic (SWEAT) connection: A hypothesis: Geology, v. 19, p. 425-428. Morris, J.D., and Hart, S.R., 1983, Isotopic and incomp atiable trace element c onstraints on the genesis of island arc volcanics from Cold Bay and Amak Island, Aleutians, and implications for mantle structure: Geochimica et Co smochimica Acta, v. 47, p. 2051-2030. Mueller, P.A., Shuster, R.D., D'Arcy, K.A., He atherington, A.L., Nutman, A.P., Williams, I.S., 1995, Source of the northeastern Idaho Batholith: Isotopic evidence for a Paleoproterozoic terrane in the northwestern U.S.: Journal of Geology, v. 103, p. 63-72. Mueller, P.A., Heatherington, A.L., DArcy, K.A ., Wooden, J.L., and Nutman, A.P., 1996, Contrasts between Sm-Nd whole rock and U-Pb zircon sy stematics in the Tobacco Root batholith, Montana: Implications for the determination of crustal age provin ces: Tectonophysics, v. 265, p. 169-179. Mueller, P., Wooden, J. Heatherington, A., and Nu tman, A., 1997, Distribution of Proterozoic crust along the NW margin of cratonic North Ameri ca: evidence from U-Pb zircon ages and isotopic systematics in young granitoids: Geological Societ y of America Abstracts with Programs, v. 29, p. A-70.

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48 Mueller, P., Heatheringtons, A., Kelley, D., Woode n, J., Mogk, D., 2002, Paleoproterozoic crust within the Great Falls Tectonic Zone: Implications for the assembly of southern Laurentia: Geology, v. 30, p. 127-130. Mueller, P.A., Burger, H.R., Wooden, J.L., Brady, J. B., Cheney, J.T., Harms, T.A., Heatherington, A.L., Mogk, D.W., 2005, Paleoproterozoi c metamorphism in the northern Wyoming Province: Implications for the assembly of Laurentia: Journal of Geology, v. 113, p. 169-179. Mueller, P., Foster, D., Mogk, D., Wooden, J., and Vogl, J., 2007, Provenance of the Uinta Mountain Group from Pb and Hf isotopic compositions of detrital zircons: Geology, v. 35, n. 5, p.431-434. OConnor, J.T., 1965, A classification for quartz-rich igneous rock ba sed on feldspar ratios: USGS Professional paper 525B, p. B79-B84. O'Neill, J. and Lopez, D., 1985, Character and regiona l significance of Great Falls tectonic zone, EastCentral Idaho and West-Central Montana: Am erican Association of Petroleum Geologists Bulletin, v. 69, p. 437-447. Pearce, J.A., N.B.W., Harris, and Tindle, A.G., 1984, Trace element discrimination diagrams for the tectonic implications of granitic rocks: Journal of Petrology, v. 25, p. 956-983. Pesonen, L.J., Elming, S.A., Mertanen, S., Pisarevski S., DAgrella-Filho, M.S., Meert, J., Schmidt, P.W., Abrahmsen, N., Bylund, G., 2003, Assemblies of continents during the Proterozoic: Rodinia and beyond: Tectonophysics, v. 375, p. 289-324. Ross, G.M., Parrish, R.R., and Winston, D., 1992, Provenance and U-Pb geochronology of the Mesoproterozoic Belt Supergroup (northwestern United States): Im plications for age deposition and pre-Panthalassa plate rec onstructions: Earth and Planetar y Science Letters, v. 113, p. 57-76. Ruppel, E.T., ONeill J.M., and Lopez, D.A., 1993, Geologic Map of the Dillon 1x2 quadrangle, Idaho and Montana: U.S. Geological Survey Map I-1803-H. Saunders, A.D., Norry, M.J., and Tarney, J., 1991, Fl uid influence on the trace element composition of subduction zone magmas: Philosoph ical Transactions of the Royal Society of London, v. 335, p. 377-392. Sears, J.W., and Price, R.A., 1978, The Siberian c onnection: A case for the Precambrian separation of the North American and Siberian cratons: Geology, v. 6, p. 267. Sears, J.W., and Price, R.A., 2000, New look at th e Siberian connection: No SWEAT: Geology, v 28, p. 423-426. Sears, J.W., and Price, R.A., 2003, Tightening the Sibe rian connection to wester n Laurentia: Geological Society of America Bulletin, v. 115, no. 8, p. 943-953.

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49 Sun, S.S. and McDonough, W.F., 1989, Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes, In Saunders, A.D. and Norry, M.J. (eds.), Magmatism in ocean basins: Geological So ciety of London Special Publication, no.42, p. 313345. Wingate, M.T.D., Pisarevsky, S.A. and Evans, D.A. D., 2002, Rodinia connections between Australia and Laurentia: No SWEAT, no AUSWUS?: Terra Nova, v. 14, p. 121-128. Winter, J.D., 2001, An introduction to igneous and metamorphic petrol ogy: Prentice Hall, Upper Saddle River, N.J., 697pp. Wooden, J.L., and Mueller, P.A., 1988, Pb, Sr, and Nd is otopic compositions of a suite of late Archean, igneous rocks, eastern Beartooth Mountains: Implications for crus t-mantle evolution: Earth and Planetary Science Letters, v. 87, p. 59-72. Wooden, J.L., and Miller, D.M., 1990, Chronologic and is otopic framework for early Proterozoic crustal evolution in the eastern Mojave Desert region, SE California: Journal of Geophysical Research, v. 95, no., B12, p. 20133-20146. Zartman, R.E., 1974, Lead isotopic pr ovinces in the Cordillera of the western United States and their geologic significance: Economic Geology, v. 69, p. 792-805. Zartman, R.E., 1988, Proceedings of the internat ional Conference on Basement Tectonics, v.8, p. 699710.

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50 BIOGRAPHICAL SKETCH Kelly R. Probst was born in Indianapolis, Indiana, in 1979. She graduated from the Business & Finance Magnet Program at Northwes t High School in 1997 with National Honors. While attending Indiana University-Purdue Un iversity at Indiana polis, she engaged in undergraduate research in the geol ogic sciences and r eceived her B.S. in geology in 2004. While attending the University of Florida, she served as a graduate teaching assi stant in the Department of Geological Sciences and also acted as department representa tive for the Graduate Student Council 2006. After completing her first year of graduate work, she accepted an internship in the mining industry, where she discovered her in terest upon graduating. She intends to pursue a professional career in econom ic/industrial geology after receiv ing her Master of Science.