Petrogenesis of Early Mesozoic tholeiite in the Florida basement and an overview of Florida basement geology ( FGS: Report of investigation 97 )

FLORIDA GEOLOGICAL SURVEY

REPORT OF INVESTIGATION NO. 97

ADDENDUM

Please attach this addendum to the inside cover of
Report of Investigation No. 97.

PAGE-

9 Figure 2 caption should also read: "Modified from Barnett
(1975) and Chowns and Williams (1983)."

10 Figure 3 caption should also read: "Modified from Puri and
Vernon (1964)."

35 Figure 11 caption should also read: "Modified from Barnett
(1975) and Chowns and Williams (1983)."

36 Figure 12 caption should also read: "Modified from Puri and
Vernon (1964)."

STATE OF FLORIDA
DEPARTMENT OF NATURAL RESOURCES
Tom Gardner, Executive Director

DIVISION OF RESOURCE MANAGEMENT
Jeremy A. Craft, Director

FLORIDA GEOLOGICAL SURVEY
Walter Schmidt, State Geologist

REPORT OF INVESTIGATION NO. 97

PETROGENESIS OF EARLY MESOZOIC
THOLEIITE IN THE FLORIDA
BASEMENT

AND

AN OVERVIEW OF FLORIDA
BASEMENT GEOLOGY

By
Jonathan D. Arthur

Published for the
FLORIDA GEOLOGICAL SURVEY
TALLAHASSEE
1988 lsgIngy o0 FLORIDO LBRARIES

SCIENCE
LIBRARY

DEPARTMENT
OF
NATURAL RESOURCES

BOB MARTINEZ
Governor

Jim Smith
Secretary of State

Bill Gunter
Treasurer

Bob Butterworth
Attorney General

Gerald Lewis
Comptroller

Betty Castor
Commissioner of Education

Doyle Conner
Commissioner of Agriculture

Tom Gardner
Executive Director

LETTER OF TRANSMITTAL

Florida Geological Survey
Tallahassee

August 1988

Governor Bob Martinez, Chairman
Florida Department of Natural Resources
Tallahassee, Florida 32301

Dear Governor Martinez:

The Florida Geological Survey, Division of Resource Management, Department of Natural
Resources, is publishing a two-part study as Report of Investigation 97. Part I "Petrogenesis of Early
Mesozoic Tholelite In the Florida Basement" interprets the origin of mafic basement rocks and discusses
chemical affinities with similar rocks in the circum-Atlantic region. This Information provides further in-
sight into the geologic history of Florida.

Part II "An overview of Florida basement geology" summarizes the lithologic and tectonic nature of
the Florida basement. As such, this section provides useful Information to scientists studying the deep
geologic strata of Florida.

Respectfully yours,

Walter Schmidt
State Geologist and Chief
Florida Geological Survey

Printed for the

Florida Geological Survey
Tallahassee
1988

ISSN 0160-0931

iv

TABLE OF CONTENTS

Page

Abstract ............... ...... ................................................ vi

Acknowledgem ents ............ ...................... ............. .......... vill

Introduction ................... .........................
M etric Conversion Factors ............ ...........................

Part I Petrogenesis of Early Mesozoic tholellte in the Florida basement .....

Background ....... ......... ....... ..........
Age .......... ..........................
Classification .......... .. ....... .......... .
Distribution .......... ..... ..............
Petrography .................. ...............
Sampling and Analytical Methods ...............
Results ..................................
Discussion ............. ................
Petrogenesis ............ .............. ..
Association .......... ..................
Conclusions ................................
References ..... .... ...........................
Appendices ..... ..............................
1. Petrographic data .......... ...........
2. Analytical accuracy and precision ..... ........ ....

Part II An overview of Florida basement geology ......... .

Discussion ................................ ....
References ..... .. .............................

. . . . . .1

... . .. . .. .. .12
....................................

.......................... .... 2
...... .............1 .... 211
.......................... . 3
...... ...................... .. 1

............... .............12

. .. .. . . . . 17
. . . . . . . . 1 7
................. ............ 27
. . . . . . . . 2 7
....... .......................28

. . . . . . . . 3 1

. . . . . . . .. 3 3

. ..... ...................... 33
...... .. ........... ..... 38

Page

1. Oil test well locations that have encountered diabase and basalt ........

2. Lithology of the pre-Middle Jurassic Florida basement surface ..........

3. Florida basement (pre-Middle Jurassic) tectonic features ..............

4. Mafic index (MI -Fe2O3*/FeaO3* + MgO) plotted versus TiOa ..........

5. Stacked plot of selected major and trace elements versus mafic index ....

.5

. . . . 10

. . . . . 14

S .. . . 15

6. Pearce and Cann (1973) Ti Y Zr discrimination diagram .............................20

v

ILLUSTRATIONS

PART I

7. Early Mesozoic pre-rift configuration of the continents .............. ................... 21

8. Mafic Index plotted versus TIO1 showing fields of circum-Atlantic tholelite ....... ............ 22

9a. Plot of TI02 versus MgO for selected ENA tholeiites ............................ .. ..... 23

9b. Plot of TIO2 versus MgO for circum-Atlantic tholeiltes .................. .. ... ......... .24

10. Plot of TI versus Zr for circum-Atlantic tholelites .......... ... ............... .......... 26

PART II

11. Lithology of the pre-Middle Jurassic Florida basement surface .... ................ .35

12. Florida basement (pre-Middle Jurassic) tectonic features .............................. ...36

TABLES

PART I Page

1. Reported radiometric age determinations for Florida tholeiite ................. ............. 2

2. Magma types recognized by Weigand and Ragland (1970) ............ .......... ..... .3

3. Major element compositions and normative mineralogy of Florida tholelite reported by Milton and
Grasty (1969) and Mueller and Porch (1983) ........................ ... ............4

4. Florida deep well data for diabase and basalt ... ... ..... .................. 6

5. Sample location data ....................... ... .. ... ... .. ..... ... ........ 11

6. Major and trace element compositions and normative mineralogy for Florida tholeiite .......... 13

7. Petrogenetic model for Florida tholeiite showing calculated compositions
and normative mineralogy ............ ........ ... ........... .. ............ 18

ABSTRACT

Thirty-nine deep oil test wells have encountered diabase or basalt In the Florida basement. These
mafic igneous rocks were emplaced prior to the onset of Atlantic sea-floor spreading during the Early
Mesozoic break-up of Pangea. Fourteen samples from eight cores passed a petrographic screen and
were analyzed by atomic absorption and x-ray fluorescence spectrometry for major- and trace-element
concentrations. Minerology of samples was determined by petrographic analysis and x-ray diffraction.
This study interprets the petrogenesis of the Florida tholelltic magma and Its relationship to other circum-
Atlantic tholelites emplaced during the Early Mesozoic. Also included In this report Is an overview of
Florida basement geology and a presentation of unpublished radiometrlc data on file at the Florida
Geological Survey.
With one exception, all samples are quartz-normative tholelites with mafic index values ranging from
61 to 87. A linear differentiation trend from a low-TI and high-Fe magma type is observed for the Florida
data. This pattern is similar to other eastern North American (ENA) tholeiitic suites; however, the Florida
magmas are more differentiated. Petrogenetic modelling suggests that 70 to 75 percent accumulation of
a fractionation assemblage consisting of 46 percent plagioclase, 45 percent clinopyroxene, 6 to 7 per-
cent olivine and 1.5 to 2 percent Fe-TI oxides may have produced the observed chemical variations.
Phenocrysts of plagioclase, clinopyroxene and olivine observed In the samples are consistent with this
model. Chemical data suggest a genetic relationship between Florida, Georgia and other ENA tholelites.
These data also suggest that the Florida and Liberia tholelites may have had the same parental magma
or different magmas of the same major element composition. No such relationship exists between
Florida and either the Surinam or Morocco diabase suites.

ACKNOWLEDGEMENTS

I express sincere gratitude to Dr. Paul Ragland for his guidance throughout the course of this study as
well as his critical review of the manuscript. I am also thankful for the critical reviews of Part One of this
study by Dr. Laura Cummins, Dr. David Whittington and Steven Campbell. Dr. Barry Cohn (Standard Oil)
and Dr. Roy Odom were helpful in providing geochronologic data for this study.
As the basement geology section expanded from two paragraphs into Part Two of this report, I am very
thankful for the encouragement, patience and Input from Dr. Thomas Scott and Dr. Walt Schmidt. I am
also very grateful for the critical review of Part Two by Dr. Jim Tull, which along with fruitful discussions
on Florida basement geology with Paulette Bond, Jackle Lloyd and George Winston (Petroconsultants,
Ltd.), led to a more comprehensive and meaningful manuscript.
David Allison is thanked for developing and providing computer graphics software used in this study as
well as his technical assistance in customizing and running the programs. Special thanks are extended
to Jim Jones, Ted Kiper and Melissa Doyle for preparing figures for this study and the associated
Geological Society of America presentation (Arthur, et al., 1988), and to Cindy Collier for typing the
manuscript.
Finally, I gratefully acknowledge those staff members of the Florida Geological Survey who reviewed
the manuscript: Ms. Paulette Bond, Mr. Ken Campbell, Dr. Ron Hoenstine, Mr. Ed Lane, Ms. Alisun
Lewis, Ms. Jacqueline Lloyd, Ms. Joan Ragland, Mr. Frank Rupert, Dr. Walt Schmidt, Dr. Thomas Scott,
Mr. Steve Spencer and Mr. Bill Yon. A cooperative agreement between the Florida Geological Survey
and the Department of Geology at Florida State University enabled all of the analytical work for this study
to be completed quickly, efficiently and cost-effectively. Loss on ignition analyses were completed by
Don Harris.

PETROGENESIS OF EARLY MESOZOIC THOLEIITE
IN THE FLORIDA BASEMENT
AND
AN OVERVIEW OF FLORIDA BASEMENT GEOLOGY

By
Jonathan D, Arthur

INTRODUCTION

Basalts are extrusive igneous rocks characteristically associated with major tectonic events such as in-
traplate or "hot spot" vulcanism, plate subduction, sea-floor spreading and continental rifting. Diabase
(or dolerite), an intrusive chemical equivalent of basalt, is primarily associated with rifting events. In
eastern North America (ENA), diabase is exposed within the Appalachian orogen from Alabama to New-
foundland as sheets (e.g., sills and lopoliths) and subparallel dikes. The sills, as well as associated basalt
flows, crop out within a series of Mesozoic basins that parallel the Appalachian orogen. Geophysical and
corehole data reveal the presence of diabase sills beneath the ENA Coastal Plain province (Gottfried et
al., 1983; Chowns and Williams, 1983). Numerous studies have suggested that the ENA diabase-basalt
suite is genetically related to Early Mesozoic rifting of the Pangean supercontinent (King, 1961; May,
1971; DeBoer and Snider, 1979). In Florida, 39 oil test wells have encountered diabase and basalt within
pre-Cretaceous sedimentary rocks. Available geochemical and mineralogical data reveal that these ig-
neous rocks are tholelitic in composition (see also Part I, "Classification" section). Based upon
stratigraphic, geochronologic, and very limited geochemical data, Chowns and Williams (1983) have pro-
posed that Florida tholelite belongs to the ENA tholelitic suite. It is possible, however, that additional
magmatic systems may have been associated with Florida tholeilte genesis due to the continental plate
configuration immediately prior to the rifting event. Plate reconstructions (Bullard et al., 1965; Van der
Voo et al., 1976), lithologic similarities (Smith, 1982) and isotopic data (Odom and Brown, 1976;
Dallmeyer et al., 1987) suggest that northwest Africa, northeast South America and southeast North
America were juxtaposed during the Early Mesozoic.
Part I of this study provides new geochemical data in order to determine the petrogenesis of Florida
tholeiitic magma(s). Furthermore, this study will investigate the possibility of a genetic relationship be-
twoen Florida and Georgia magmas and those magmas represented by tholeiitic dike systems of Africa
and South America which were emplaced during the break-up of Pangea. Existence of such a relation-
ship would further support theories regarding the Early Mesozoic rifting event and provide further insight
into the geochemical nature of tholeilte prior to generation of mid-Atlantic ridge transform and ocean-
floor basalts.
Part Two of this report summarizes Florida basement geology. Included in this section is a presenta-
tion of nomenclature currently recognized by the Florida Geological Survey as well as unpublished
radiomotric data on file at the Survey.

Metric Conversion Factors

The Florida Geological Survey, in order to prevent duplication of parenthetical conversion units, inserts
a tabular listing of conversion factors to obtain metric units.

Multiply By To Obtain
feet 0.3048 meters
miles 1.6090 kilometers
inches 25.40 millimeters

PART I PETROGENESIS OF EARLY MESOZOIC
THOLEIITE IN THE FLORIDA
BASEMENT

Background

AGE

A comparison of geochronological studies of Florida diabase suggests that the average age of
crystallization is about 192 million years (Ma) (Milton and Grasty, 1969; Barnett, 1975; Mueller and Porch,
1983). Results of these studies are summarized in Table 1. Only those age determinations from
unaltered diabase and basalt with uncertainties less than 15 Ma were considered for this average.
Several studies have noted a lack of reproducibility in K-Ar ages for ENA diabase due to K or Ar in-
homogeneity, radlogenic 40Ar loss (Armstrong and Besancon, 1970) or an excess of radiogenic 40Ar
(Dooley and Wampler, 1983). Sutter (1985) notes that 40Ar/39Ar ages are more reproducible than K-Ar
ages. For these reasons, the 40Ar/3Ar age determinations reported by Mueller and Porch (1983) for
Florida diabase (averaging 194 9 Ma) may be closer to a true age of crystallization. A compilation of
age determinations for diabase beneath the Coastal Plain of the southeastern United States can be
found in Chowns and Williams (1983, Table 6). For diabase in the subsurface of Georgia, their tabulated

Table 1. Reported radiometric age determinations from Florida
rock, MS mineral separates)

Florida
Geol. Survey Rock
County Well Number Depth (Ft.) Description

Method

tholeiite. (WR whole

Age (Ma) Reference

Dixie Gainesville
(offshore) BIk. 707, #1

Franklin

Franklin

W-8487

W-8487

12,450

14,275

14,275

Altered Basalt

Diabase

Diabase

K-Ar WR

K-Ar WR

244 10 Standard Oil,
unpublished data

203
182
186
195

K-Ar MS 153
(Pyroxene) 181
129

Barnett (1975)

Barnett (1975)

Hardee

Hardee

W-1655

W-1655

Highlands W-966

Lee

W-10566

11,853

11,870

12,664

15,708

Highly Altered
Basalt

Basalt

Slightly Altered
Basalt

Basalt
(Composite)

K-Ar WR

40Ar/39Ar
WR

K-Ar WR

K-Ar WR

147 3
143 7

192 7
196 6

Milton and Grasty
(1969)

Mueller and Porch,
(1983)

183 10 Milton and Grasty
(1969)

163 ?

Barnett (1975)

results yield an average crystallization age of 194 11 Ma. Summarizing geochronologic Investigations
of ENA diabase dikes, Cummins (1987) reports that crystallization occurred between 175 and 200 Ma,
probably toward the lower (older) end of this range. Emplacement of the Florida and Georgia subsurface
tholeiites was apparently synchronous with that of the average ENA tholeiltic suite.

CLASSIFICATION

Early studies of ENA diabase have noted that the rocks are essentially uniform in chemistry and
mineralogy (e.g., Walker, 1969). Weigand and Ragland (1970), however, in a geochemical study of
diabase dikes, recognized four parental magma types based upon TIO2 content, mafic index (MI) values
(calculated as Fe203*/(Fe203* + MgO), total Fe(*) as Fe2O3a and normative mineralogy (Table 2).

Table 2. Magma types recognized by Weigand and Ragland (1970). Abbreviations with asterisk
taken from Ragland and Whittington (1983).

MAGMA TYPE ABBREVIATION TIO2 (WT.%) MAFIC INDEX

High-TiO2, quartz-normative HTQ* > 0.9 > 57

Low-TiO2, quartz-normative LTQ* < 0.9 > 57

High-Fe203, quartz-normative HFQ* > 0.9 > 74

Olivine-normative OLN

This fundamental classification is currently applied to all ENA tholeiitic intrusives and extrusives;
however, the HFQ variety has more recently been recognized as a differentiate of the HTQ and LTQ
parental magmas (Maxey, 1973; Ragland and Whittington, 1983). Puffer and Philpotts (1988) have
recognized two fractionation trends that evolve toward two high-Fe "sub-type" magmas in the north-
eastern United States: an incompatible element enriched (IEE) pattern that includes the average HTQ
magma composition and an incompatible element depleted (IED) pattern that is equivalent to an LTQ-
HFQ trend (based upon Weigand's (1970) averages), Gottfrled et al. (1986) have added three new groups
(or subgroups) to the Weigand and Ragland (1970) classification based upon rare earth element and Sr-
isotope concentrations. These three groups are not considered in this report because the discriminating
geochemical variables were not analyzed. Cummins (1987) recognized three petrographic groups for
diabase dikes in Virginia. These groups included (1) olivine-spinel bearing (OSB); (2) granophyre bearing
(GRB); and (3) spinel-granophyre absent (SGA).
Six whole-rock major element analyses have been reported for Florida's subsurface tholelite (Milton
and Grasty, 1969; Mueller and Porch, 1983). Normative mineralogy and chemical data for these six
samples, shown in Table 3, Indicate that the HTQ, LTQ, HFQ and OLN magma types are present in
Florida. Although only one sample from Florida (MP-14, Table 3) belongs to the OLN group, 12 of 18
tholelites from southern Georgia are olivine normative (Chowns and Williams, 1983).

Table 3. Major element compositions and normative mineralogy of Florida tholeiite reported by
Milton and Grasty ("MG" samples; 1969) and Mueller and Porch ("MP" samples;
1983). [MI calculated as Fe203*/Fe2O3* + MgO, normative minerals calculated on a

dry basis with Fe3+/Fe2+ = 0.1, *

Weight
Percent
SIOa
TO12
A1203
Fe203
FeO
MnO
MgO
CaO
Na20
K20
PzO0
Volatiles
TOTAL
MI

Rb(ppm)
Sr(ppm)

MG2
46.8
0.83
17.1
3.5
6.1
0.11
10.5
3.2
1.2
3.3
0.12
6.5
99.3
49.3

NR
NR

1.78
6.40
21.02
10.94
16.40
0
36.51
0
5.47
1.68
0.28
St. Lucle
W-4323
Amygdaloldal
Basalt

- Total Fe, NR Not Reported],

MG5
50.9
1.2
16.6
4.3
4.6
0.08
6.2
6.3
3.3
0.57
0.17
4.9
99.1
60.1

NR
NR

6.50
0
3.62
29.61
30.37
1.27
19.25
0
6.62
2.39
0.39
Taylor
W-1877
Dlabase

MG6
52.8
1.1
15.3
2.2
9.9
0.22
4.4
8.9
2.5
0.68
0.17
1.6
99.8
74.8

NR
NR

6.96
0
4.09
21.53
28.90
12.31
20.49
0
3.25
2.10
0.38
Taylor
W-1877
Diabase

MP12
53.65
1.73
13.47
NR
13,20'
NR
3.99
7.63
2.56
1.35
NR
NR
97.6
78.4

43
268

7.07
0
8.17
22.18
21.66
14.14
21.31
0
2.16
3.33

Hardee
W-1655
Basalt

MP13
52.87
1.79
12.83
NR
14.00'
NR
3.87
8.29
2.51
1.01
NR
NR
97.2
79.9

35
292

6.98
0
6.14
21.84
21.23
17.57
20.50
0
2.30
3.46

Hardee
W-1655
Basalt

MP14
47.08
3.45
18.21
NR
12.95"
NR
9.25
7.02
2.58
0.29
NR
NR
100.8
60.6

5
348

0
0.78
1.70
21.63
34.63
0
21.25
12.24
2.04
6.43

Highlands
W-966
Altered
Basalt

Weight
Percent
Norms
Quartz
Corundum
Orthoclase
Albite
Anorthlte
Dlopslde
Hypersthene
Olivine
Magnetite
Ilmenlte
Apatlte
County
Well No.
Description

4(101-117)

EXPLANATION

Corehole location

() Rnallometrlc age determlnatlons
available for tholellte (see Table 1)

22 Corehole reference number
(see Table 4)

(102-122) Zr concentrations (ppm)

0 25 50 MILES

0 40 80 KILOMETERS

t A e-"4-
d

Figure 1. Oil test well locations that have encountered diabase and basalt,

DISTRIBUTION

Oil test wells In Florida that have encountered diabase or basalt are shown on Figure 1. The number
adjacent to each well on Figure 1 corresponds to the left hand column on Table 4. Other information sum-
marized in Table 4 Includes specific well localities, references indicating types of data that are reported
for each well and depth Intervals that contain diabase or basalt.

Table 4. Florida deep wells that have penetrated diabase or basalt (modified from
Lloyd, 1985, and lists only wells that have been previously described). Well
locations are shown in Figure 1.

WELL NO.
COUNTY PERMIT NO,

DEPTH TO
TYPE OF THOLEIITE/
ELEV. OF TOTAL DEPTH 'REFERENCE- THOLEIITE PENETRATION
WELL NAME LOCATION WELL, FT. OF WELL, FT. DATA ENCOUNTERED THICKNESS. FT.

Columbia W.1709
P.77

Humble Oil & Re-
lining Co.,J.P.
Cone No. 1

Sec, 22
TINR17E

4444 2-1 Diabase and amyg.
6.1. 2 daloidal basalt
9.2, 3, 4 encountered in
black shale

2 DeSolo W-12393
P-670

3 Dixie
(Ofllhore)

4 Franklin W-8487
(Offshore) P-387

5 Franklin W-5654
(Offshore) P-293

6 Hardee W.1655
P.62

Highlands W.960
P-B-1

8 Highlands W-3578
P-226

9 Hlllsborough W-1005
P.29

10 Holmes W-12199
P-710

11 Indian River W-3783
P-243

12 Jackson W-1886
P-94

Amoco Prod. 1 Sec. 19
Opal Knight T30S, R27E

Sohlo,
Gainesville
707, #1

OCS
Galnesville
Block 707

Mobil Prod, 1C 29037'54"N
State Lease 224A 8500'OB"W

Calif. Co. and
Coastal Pot,
Co., No. 2

Humble Oil & Re-
fining Co. -
B.T. Keen No. 1

Humble Oil & Re-
fining Co. C,C.
Carlton Estate
No, 1

Continental Oil
Co. C.C. Carl.
ton et al. Well
No. 1

Humble O11 & Re.
fining Co. T.S.
Jameson No, 1

29'47'57,6"N
6422'42.50"W

11655

12453

14369

10560

11934

Sec. 23
T35S, R23E

Sec. 34
T3OS, R28E

Sec. 20
T38S, R28E

Sec. 7
T31S, R22E

12985

12630

10129

11201

Sonat Expl. Sec. 32
Randall Hughs T4N, R17W

Amerada Pet,
Corp. Fonden
Mitchell Well
No. 1

Humble Oil Re.
fining Co. C.W.
Tlndel No, 1

Sec. 28
T31S, R35E

Sec. 8
T5N, R11W

7-1 Jurassic diabase 11627/28

Standard
Oil (unpub.)
1,5

6-1, 2
7-1, 2, 5

Altered
basalt

Diabase

6-1.2 Diabase-basall

2-1
4-2
5-2, 5
6-1, 2
83, 4, 5
9.2, 3, 4

Lava & pyroclastic
rocks, basalt

2.1 Amygdaloidal ba-
5-2, 5 salt, rhyolite por-
6-1, 2 phyry and related
8-3. 4 volcanic rocks

3-1
6-1.2
9.2, 3, 4

2-1
4.2
6-1, 2

Pro.Mesozoic?
volcanic rocks

Basalt

12453/4

13926137

10460/10
10520/10

11826/106

12618/387

12602/28

10115/10

71, 2 Diabase, greenish 10940
& weathered top 10940

9488 3-1 Amygdaloldal
6-1,2 basalt, diabase

9245 2-1 Triassic (?) basalt
In Paleozoic
strata

FIGURE 1
MAP LOCATION
NUMBER

3529/33
3564/1
4191/1
4193/2
4248/3
4267/3

9444/45

8890/42

-1

Table 4. (Continued)

FlO(iUtE
MAP L (K:AIION WELL NO
NIIMRFII COUNTY PERMIT NO

I J(effeion W 1854
P.95

1I lelfferiqoi W. 1091
P 468

li I |Ik W 114*l
P 1/4

it l on W. 101S0,
P 401

t1 .oI W 12 9:1
P III

WELL NAME

Coastal Pel Co
E P Larsh No I

Amoco Prod 1 -
uickoye

innmillon Bros 1
Keen

HIumble I Lehigh
Acres

Phillips Part
I SI Joe A

LOCATION

Sec. 1
T28, R3E

Sec 17
T28, RSE

Sec 25
T209, R28E

Sec. 14
T459, n27E

Sec 14
T2S. nlE

ELEV. OF
WELL, FT.

St

55

92

67

33

TOTA
OF W

L DEPTH REFERENCE
ELL, FT, DATA

7913 2.1
8.1,2
0-2. 3, 4

7034 7-1

8397

18710

10466

7.1

7.1, 2, 5

7.1

iH irvy W ;012
1' 10t

I I lrnMly W 124 M

.'0 Manlioli W t159
No Permit

1 Malison W. t 08
No Permit

f Madiso W. Iot
P 1033

/. Nassau W 331
No Permit

N4 Nassau W 10715
No Permit

4 O()lokx) W 11467
P 590

()Okomchohat W 37:19
P 23?

I ()Okeehobee W. I;541
P 110

k OkLeechbes W.12542
P 732

/ Pasco W-12399
P.143

Humble Oil A Ro Sec 19
inning Co C E TOS. RI /E

Robinson No I

Plndrt Oil 26 4
USA

Hunt Oil Co
J W Oibson No 2

Huint Oil Co
J W Oibson No 4

Oilman Paper Co
No 22 2

St Marys River
Oil Corp -
Hilliard Turpen-
line Co No 1

Amoco Prod
2. 1 T Rayonler

Sonal Expl I
JO Moore 311

Amerada Pelt
Corp Marle
Swenson No 1

Shell Oil 1 -
Shall Sloan 35 1

Shell Oil 1 -
Jean M Davls

Amoco Prod Co.
I Larkin Co
8.4

Sec 26
T38, R5W

Sec 6
TIS. R10E

Sec 5
t2S. ItlE

Sec 5
T28, ROE

Sec 19
T4N, R24E

See 50
T3N, R27E

Sec 3
T3N, R24W

Sec 5
t38, R34E

Sec 34
T358, R36E

Sec 9
T358, R35

Sec 6
T258, R22E

4009 2.1 Trlassic (?) basalt 4344133
.1, 2

12131

5385

4006

10140

9-2, 3, 4

7.1

2.1
S1, 2

2.1

9-1

4824 1.1
2.1
7.1,2
92., 3, 4

5408 7-1
9-2, 3, 4

14514 7.1

10838 3-1
6-1,2

11277 7.1

10767 7.1

7148 7-1, 2

Dlabase

Triassic (?) diabaso

Triasslc (7) diabase

Altered dlabase

Trlasslc (7) diabase

12060/10
12095/38

4580139

4044/18

6450/120
6800/400
92001100

4808/18

Trlasslo dlabase 6180/16
5310/15
6418/51

Dlabase or basalt

Pre.Molozolc?
volcanic rocks,
basalt

Weathered dlabase

Weathered dlabase

Weathered auglte
dlabas
(JuraiMo)

14420/94

10750/88

11220/57

10842/103

7129119

TYPE OF
THOLEIITE
ENCOUNTERED

Triasll (?) dlibase
& related Ignoous
rocks

Dlabase
Gabbrolo diabase
Oabbrolc diabase

Weathered basic
igneous rock

Altered quartz
diabase

Engle Mills fm.
Diabase

DEPTH TO
THOLEIITEI
PENETRATION
THICKNESS, FP

7783/29
7850140

0698/8
0730/13
6703/131

6105/202

15876/35

8450/2010
8488188
9208140
931015
9350/10
938012
939418
9430/29
10230/33

__I

Table 4. (Continued)

WELL NO.
COUNTY PERMIT NO.

'TYPE OF
ELEV, OF TOTAL DEPTH REFERENCE THOLEIITE
WELL NAME LOCATION WELL, FT. OF WELL, FT. DATA ENCOUNTERED

30 Polk W.8741
P-403

31 St. Lucia W.4323
P-259

32 Taylor W.1077
P.86

33 Taylor W.2099
P.116

34 Taylor W.2108
P-119

35 Taylor W.10912
P.480

30 Taylor W.15446
P.112

37 Wakulla W.12114
P.690

38 Wallon W.11374
P.887

39 Washlnglon W.12347
P.738

Sun Oil 1 80,. 19
Shepard Dairy T328, R27E

Amorada Potr.
Corp. Cowlos
Magazine No. 2

Humble Oil & Ro.
fining Co. G.H.
Hodges No, 1

Gulf Oil Corp. -
Brook -s Scanlon
Inc., Block 42
No. 1

Gull Oil Corp, -
Brooks Scanlon
Inc,, Block 33
No. 1

Soc. 19
T368, R40E

8oc. 12
T68, ROE

Soc. 9
T88, ROE

Bec. 18
T48. ROE

Amoco Prod, 1 Soo. 12
Canal Tbr. Co. T38, ROE

Amoco Prod.
Buckoyo Collu,
7-4, #1

9670 71, 2 Allored diabaso
(Jurassic)

12478

4.2
5-2, 3
8.1,2

6264 2.1
6.3
0.1, 2
9.2,3, 4

Diabaso

Triassic? basallic
rock
Triassic? diabase
gabbro

6430 2.1 Triassic? diabaso,
0.1,2 prob. a lava flow

6243 2.1 Triassic? diabaso
gabbro

7036 7-1 Diabaeo

9000 NA Maflc Ignoous

8oc. 7
T48, ROE

Placid Oil Co. 1 Soc. 27
USA Unit 27.2 T28, R3W

Texas Gas Expl.
1 Inlernatlonal
Paper Co.

8oo. 6
T6N. R20W

12242

12028

14044

Hunt Polt.-Int. 800, 11
Paper Co. T4N. R14W

7-1 Diabaso

7.1 Diabaso

7.1 Diabaso

Reference: 1 Cole, 1944; 2- Applln, 1951; 3. Applln and Applln, 1965; 4. Bass, 1909; Milton and Grasty, 1069; 6. Milton, 1972; 7 Barnotl, 19756 8 Muollor and Porch. 1983; and 9 Prosont Study.

Data: 1 Magascoplo Description; 2 Petrography; 3 Major Eloment Chemistry; 4 Trace Elemont Chomistry; and 6 Radlomolric Ago(s).

FIGURE 1
vAP LOCATION
NUMBER

DEPTH TO
THOLEIITE/
PENETRATION
THICKNESS, FT.

9660/10

12734/appr. 10

0163/12

0165/89

5438179

5200/43

6256/113
6417/247
6708/85

6270/125

12220/22

11810130
11997/31

10840/20
13390/10
13470/30
13510/10
13670/50

"I- I

I ~-I----I- ------~- -`-~-~------ -Y~` ~-~----"` -~-U~L~I" -I I--Y-

-- --

Figures 2 and 3 show the generalized lithology and structure of the Florida basement, respectively (see
Part Two for further discussion). A comparison of these figures with Figure 1 reveals that intrusions of
basalt and diabase most commonly occur in the Mesozoic basins of Florida and are least common in the
igneous terrane of central Florida. The exact Intrusive form of each tholelitic body is unknown. In general,
these rocks occur as dikes, sills (or sheets) and flows, but detailed core descriptions, additional
petrographic analyses and geophysical data are required in order to be more specific.
The variation in depth to these mafic rocks is predominantly controlled by their geographical position
relative to the Peninsular Arch. For example, diabase is encountered at a depth of approximately 3,500
feet in Columbia County, whereas in Wakulla and Hardee Counties, diabase or basalt is present at a
depth of approximately 12,000 feet (Figure 3 and Table 4). The position (depth) of these rocks relative to

EXPLANATION

: Trfinsmic rod lbods and
L dJ lhniso Intruislons
i Earlly Ito Middlo Mosqotroc hypabysial
ll= 4nd ox)itslveo Iimnic rocks

O(rrdoviclrn )Dovonlan sodlimnontiry rocks

fi. Lti Procar:nmrin Early Cambrinn
f(ol se I nlrisivo rocks
SLaito Procmbnrial)l Early Cannlrlan
f lsic: oxlriisivo rocks

f Approximate contact

? DoI) tlos arona for which thoro nro conlllcting
dtsci(lptions or n lack of datla

0 25 50 MILES
0 40 00 KILOMETERS
0 40 so KILOMETERS

'9'.B.

Figure 2. Lthology of the -Middle urassic Florida basement surface
Figure 2. Lithology of the pre-Middle Jurassic Florida basement surface.

the post-rift unconformity as well as petrographic evidence (fine grained and vesicular textures) suggests
that emplacement and crystallization of these tholeiitic melts was at or near the surface. An eight to ten-
thousand foot variation in present-day depth to these rocks does not reflect the initial variation in their
original depth of emplacement. Variations in topography during emplacement caused the initial dif-
ferences, especially for the extrusive rocks. Post-Middle Jurassic subsidence of the flanks of the Penin-
sular Arch has further changed the apparent relative depth of emplacement (or extrusion) of these
tholelitic rocks.

\ kSIN
O

EXPLANATION

- Syncllirnl nxls

+ Antlclinal axlis

/ 0 Approximato bnsin limits

0 25 50 MILES
0 40 80 KILOMETERS
0 40 80 KILOMETERS

o ,
,,ev

Figure 3. Florida basement pre-Middle Jurassic tectonic features.

PETROGRAPHY

The major mineral constituents of diabase are calcic plagioclase and clinopyroxene, most commonly
augite but also pigeonite, with or without olivine and orthopyroxene. Petrographic descriptions of 11
Florida diabase or basalt samples have been previously reported (Bass, 1969; Milton and Grasty, 1969;
Barnett, 1975). In general, the rocks they describe contain about 50 percent plagioclase (most commonly
labradorite), 40 percent clinopyroxene augitee), 10 percent accessory minerals or alteration products and
occasionally trace amounts of olivine. The most common accessory phases are opaques
(titanomagnetite?), granophyre (intergrowths of quartz and potassium feldspar), biotite, apatite, sphene,
epidote and calcite. Alteration of augite and olivine is indicated by the presence of chlorite, magnetite,
montmorillonite, iddingsite and serpentine. Plagioclase occasionally alters to sericite. Diabase textures
range from fine to medium grained, equigranular-intergranular to subophitic. Basalts analyzed in this
group are very fine grained and holocrystalline. Porphyritic textures contain a phenocryst assemblage of
either plagioclase, clinopyroxene plus plagioclase, or olivine.
Petrography of samples listed in Table 5 is tabulated in Appendix 1. These new data are in general
agreement with published results; however, olivine is not observed in any of the Florida Geological
Survey (FGS) samples. One must conclude that either the occurrence of olivine tholeiite in Florida is rare
or that the sampling screen (see next section) for this study created a bias. In general, textures of the
FGS samples are equigranular-intergranular and occasionally subophytic. Porphyritic samples contain
plagioclase or plagioclase plus clinopyroxene phenocrysts. With respect to Cummins' (1987) classifica-
tion, the FGS samples belong to the granophyre-bearing (GRB) and spinel-granophyre absent (SGA)
petrographic groups.

Table 5. Sample location data.

LAB. NO.
FGS-1
FGS-2
FGS-3
FGS-4
FGS-5
FGS-6
FGS-7
FGS-8
FGS-9
FGS-10
FGS- 11
FGS-12
FGS-13
FGS-14

COUNTY
Taylor
Taylor
Taylor
Highlands
Nassau
Hardee
Levy
Levy
Columbia
Columbia
Jefferson
Nassau
Nassau
Nassau

WELL NO.
W-1877
W-1877
W-1877
W-3578
W-336
W-1655
W-2012
W-2012
W-1789
W-1789
W-1854
W-10715
W-10715
W-10715

DEPTH OR DEPTH INTERVAL
(FT.) BELOW MSL

6180
6207
6228
12614
4820
11888
4350
4356
3529.5
3555
7789
5429
5437
5444

6219
6246
12629
4822
11932
4360
4359
3555
3562
7791

MAP NO.
(FIGURE 1)
32
32
32
8
24
6
18
18
1
1
13
24
24
24

SAMPLING AND ANALYTICAL METHODS

Table 5 shows the county, well number and depth interval for 15 diabase and basalt samples from the
Florida Geological Survey core repository in Tallahassee, Florida. Map numbers listed on Table 5 corre-
spond to core hole locations shown on Figure 1. Cuttings and core chips from the depth intervals listed
for each well in Table 4 were petrographically screened in an attempt to yield only homogeneous, fresh
and aphyric samples for geochemical analysis by atomic absorption (AA) and x-ray fluorescence (XRF).
All samples were powdered in a Siebtechnik tungsten-ring rock pulverizer and split prior to analysis. A
thin section from each core was also prepared. Petrographic identification of alteration products was
facilitated by a Philips APD 3520 x-ray diffractometer. Loss on ignition (LOI) was determined
gravimetrically by measuring the weight loss of a one-gram powder sample after being heated in a muffle
furnace for one hour at 8000C. Solutions for AA analysis were made from rock powders using a
hydrofluoric-boric acid microwave dissolution technique modified from Langmyhr and Paus (1968). Con-
centrations of Na, Fe (total Fe as Fe203) and Mg were determined on a Perkin-Elmer model 303 atomic
absorption spectrometer modified with a digital signal integrator. In preparation for XRF analysis, sample
powders were mixed with a boric acid binder (7:1) and pellet-pressed into Spec-caps. The pellets were
analyzed by an automated Philips PW 1410 x-ray fluorescence spectrometer (W-tube) for the major
elements Si, Ti, Al, Mn, Ca and K, and the trace elements P, Ba, Cr, Cu, Ni, Rb, Sr, V, Y, Zn and Zr.
Calibration curves for each element were set up using the following rock standards: USGS-W-2,
USGS-BCR-1, QMC-1-3, USGS-DNC-1, USGS-AGV-1 and GSJ-JB-1. Analytical precision was calculated
as coefficient of variation (CV) from duplicate analyses of all samples. Acceptable values of CV for major
and trace elements are less than 3 percent and 10 percent, respectively. All major and trace elements fall
within this range except for Cu, Rb and Y (< 20 CV). Accuracy was determined by comparison of observ-
ed versus expected values for U.S. Geological Survey standards W-2, DNC-1 and BCR-1. These results,
as well as precision analyses, are summarized in Appendix 2.

Results

Major and trace element chemistry, mafic index and normative mineralogy (a calculated, theoretical
mineral assemblage) of samples collected for this study are listed in Table 6. Although five samples have
a high volatile content (greater than 2 weight percent loss on ignition), indicating significant alteration,
most of the samples appear to have retained their original geochemistry. Alteration of sample FGS 9 may
have lowered the silica concentration enough to change its normative mineralogy from quartz- to olivine-
normative. Note that a composite sample (FGS 10) taken from the same core a few feet lower is quartz-
normative.
Of the six Florida tholeiite samples previously analyzed (Table 3), only three are included in the present
data base. Samples MG 2 and MG 5 are excluded due to evidence of alteration (high concentrations of
K20 and/or volatiles greater than 5 percent). Sample MP 14 is excluded for the following reasons (1)
despite its apparent low volatile content, Mueller and Porch (1983) report that the sample is altered; (2)
MP 14 is olivine-normative and plots far from any of the observed geochemical trends (the petrogenetic
significance of a magma type (OLN) based upon one sample is highly speculative); and (3) Hurtubise et
al. (1987) suggest that MP 14 belongs to an Upper Jurassic-Lower Cretaceous alkalic magma intrusion
episode. Due to the questionable OLN character of FGS 9, all samples are classified as quartz-normative
tholelites. In the following discussion, the Florida tholeiite data base consists of all FGS samples and
samples MP 12, MP 13 and MG 6 (Table 3).
There appears to be no systematic chemical variation in the samples with respect to geography. The
distribution of Zr on Figure 1 is shown as an example. Chemical variation between samples in a given
core (same intrusion) is observed in some cases. A comparison of Tables 5 and 6 reveals that individual
(?) Intrusion chemistry ranges from strongly differentiated (e.g., W-1877, mafic index (MI) ranges from
69.8 to 87.7) to very homogeneous (e.g., W-10715, MI ranges from 70.7 to 71.7).

Previous studies indicate that all four magma types of Weigand and Ragland (1970) are present in
Florida. However, when considering the accepted data base, only the LTQ and HFQ (and OLN?) types
are present. These data plot as a linear trend from the LTQ field through the HFQ field on the MI versus
TiOa diagram of Figure 4. As expected, the samples with a granophyric texture (Appendix 1) plot on the
more differentiated portion of this trend (higher MI values).
All major and trace elements have been plotted as dependent variables against the MI. Concentrations
of SiO2, TIO2, FeaO3*, Na2O, KaO, P2Os, Ba, Cu, Rb, V, Y, Zn and Zr increase with increasing MI values
(positive slope), whereas concentrations of A1203, MgO, CaO, Cr and Ni decrease with increasing MI

Table 6. Major and trace element compositions and normative mineralogy of Florida
tholeiite. MI calculated as Fe2a03/Fe203* + MgO, total Fe as Fe203', nor-
mative minerals claculated on a dry basis with Fe3 + /Fe2 + = 0.1, BD below
detection. See Table 3 for explanation Norm Abbreviations.

Pt:CFNr FOSI (IS2 F0S3 FOS4 FOS5 FOS6 FOS7 FOSO FOSO FOSI0 FOS11 FGS12 FOS13 FGSI4

)SO, 53 52 52 1 51 0 51.5 51 7 520 528 48.4 50.8 51.2 51.9 51.0 62.2
r0, 2 Is 095 I 20 1 26 0.70 1.05 1 00 1.80 1.23 1.20 0.82 1.32 1.35 1.32
AljO) 1 1 14 1 138 133 130 13.1 13 1 13.1 13.1 13.4 13.0 136.8 13. 13.0
F *oi' 1/H 124 138 110 110 140 13.1 14.1 14.5 14.2 10.9 13.2 13.3 13.4
Mno 022 019 021 004 021 022 0.15 0.18 0.22 0.22 022 0.22 0.22 0.22
M TH 2 :1/3 598 488 7 08 421 3.02 3.74 8.60 6.73 7.13 5.2 6.53 .649
C.t) 43 9 63 102 105 113 8 13 8.25 6.88 9 34 10.7 11.0 0.82 9,92 9.76
NaO ;2 14 2 99 244 248 205 2.38 280 2.75 2.80 2.18 2.16 2.65 2.42 2.60
K,O I 04 0 R61 037 0.18 1 30 1.82 1.75 031 0.23 0.20 0.51 0.80 0.07
P,a 0.) 011 0 15 010 009 044 0.35 037 0.13 0.17 0.09 0.25 0.22 0.25
LOt 0 l 0 12 053 4092 1 7 260 4.82 2.31 2.91 1.22 2.01 1.66 0.63 0.50
IOIAt 101 / 9 11 1010 999 1005 1010 101 7 99.8 99.5 101.1 99.3 100.1 99.5 100.2
Mt /l its 5 9 a 69 4 50.9 780 013 790 08.8 67.9 60.5 71.7 70.7 70.9

PE!CIINI
NO(RMH

( / 1 3 53 2149 592 325 5.51 5.78 8.22 0.00 2.00 3.37 4.45 3.03 3.70
(H / 74 5 12 363 233. 008 8.48 11.2 10.7 1.92 1.38 1.23 3.10 3.82 4.02
AH 2:1 .I 21 208 221 17 8 20.7 24.7 24.2 24.8 18.7 19.0 22.2 20.9 21.3
AN 19 249 250 25 1 294 21.4 18.5 18.7 23.3 28.4 27.8 24.7 26.4 24.9
I1 1;34 194 204 235 223 14.4 18.5 11.9 19.9 21.5 22.9 19.6 19.3 10.7
HY 21 5 1 1n 231 158 240 22.5 14.9 21.0 18.4 25.2 22.4 20.9 22.1 22.2
01 000 000 000 000 000 0.00 0.00 0.00 6.68 0.00 0.00 0.00 0.00 0.00
MI 200 1 8 202 170 1.4 224 1.98 2.13 2.21 2.09 1.88 1.97 1.97 1.97
tL 40/ I 84 227 252 1 46 3.77 3.70 3.63 2.42 2.46 1.60 2.55 2.59 2.52
AP 0(16 038 033 0 42 0 20 099 0.80 0.85 0.30 0.38 0.20 0.56 0.49 0.55

PPM

oa 253 160 152 151 115 289 335 392 156 185 126 189 193 201
Cr 80 BD BO 141 253 BD 00 B 677? BD 228 BD BD BD
C( 289 80 109 45 85 193 154 187 125 14? 87 57 53 55
N I1 23 37 55 85 28 42 31 75 77 85 32 30 33
fib 36 26 17 10 11 26 52 53 11 10 12 18 23 20
So 114 153 128 241 132 243 224 226 152 127 129 138 230 223
V :100 231 283 272 241 313 310 329 307 311 251 301 294 294
Y 55 29 31 19 26 35 38 36 32 41 24 24 22 33
In 186 89 94 195 00 128 143 117 101 103 78 108 102 100
/t 197 122 105 102 83 174 178 182 89 100 85 117 101 111

values (negative slope). No correlations are observed for MI versus MnO and Sr. Figure 5 is a stacked
plot of the elements that best correlate with the MI. Trends with positive slopes indicate that the element
was not Incorporated into the phases that fractioned from the magma, that is, the element was incompati-
ble. Compatible elements (e.g., CaO and Ni) have negative slopes and were thus removed from the
magma during fractionation.
The trends shown on Figures 4 and 5 suggest that the data represent a single suite. Some of the data
which constitute trends on Figures 4 and 5, as well as subsequent diagrams, may prove to represent por-
tions of other trends not yet delineated due to limited data.

96.0 -

88.0 -

*FGS1

X
UJ
W

Z 80.0

U-

72.0

64.0

56.0 -
0.40

FQS2

/ *MG6
I I
SHFQ FGS12/
S FGS14L FGS13
3 FQS3 t -
,FQS 9-"FGS4
FGS10

I-
i / HTQ
I /
1611

0.80

1.20

1.60

FGS7
MPI3 FG7
FGS8
P *FGS6
MP12

00
2.00

T102 (wt.%)

Figure 4. Mafic index (Fe2Oa*/Fe203* + MgO) plotted versus TiO2 (weight percent). Modified from
Welgand and Ragland (1970). HTQ is high-TiO2, quartz-normative; HFQ is high-Fe2Oa,
quartz-normative.

2.40

- -

12.0

10.0

0
S8.00
*

6.00

15.2

? *
14.4

0
S13.a

12.8

0.80

0.40

i.* .
0
C 0.20

0.00

2.40

R 1.8 0

0
0.80

0.00,

55.0 80.0 65.0 70.0 75.0 80.0 85.0 90.0
MAFIC INDEX

Figure 5. Stacked plots of selected major and trace elements versus the mafic Index.

%

0-%
C 150
CL
N
100

50

120

E
& 80

40

0

30

0*

0g

.00

.0

56.0 80.0 65.0 70.0 75.0 80.0 85.0 90.0

MAFIC INDEX

Figure 5. (Continued).

200

0*

10

0

200

E
a.eo

N
120

80

"404P

Discussion

PETROGENESIS

The petrogenetic relationship between the high-TI02 quartz-normative (HTQ), low-TiO2 quartz-
normative (LTQ) and olivine-normative (OLN) magmas in eastern North America (ENA) has not been
totally resolved. One explanation suggests that the HTQ and LTQ magmas are the result of varying
degrees of plagioclase, clinopyroxene and olivine fractionation of OLN magmas (Weigand and Ragland,
1970). Smith et al. (1975) contend that olivine fractionation of OLN produced the LTQ; whereas, the same
process plus assimilation of orthopyroxene produced the HTQ. In accordance with Green and Ringwood
(1967), both of the above studies agree that the OLN magma was produced by partial melting of an upper
mantle source. Later studies suggest that the diverse chemistry of these magmas was due to incompati-
ble element wall-rock contamination (Ragland et al., 1971) or magma mixing (Pegram, 1983).
The linear trend on Figure 4 supports the result of previous ENA diabase studies (e.g., Maxey, 1973;
and Cummins, 1987) which indicate that the LTQ magma is parental to the high-Fe20O quartz-normative
(HFQ) magma. The Florida tholeiitic suite, however, is much more evolved than any ENA diabases
previously reported. The data plot well beyond the HFQ field toward a maximum MI value of 87. A
petrogenetic model for the Florida tholeitte must account for this as well as the compatibility of AI203,
MgO, CaO, Cr, and Ni within the fractionating assemblage.
The phenocryst assemblage within the Florida samples can account for most of the observed major
and trace element variation. Based upon experimentally determined partition coefficients (Henderson,
1982), fractionation of clinopyroxene from a basaltic magma would noticeably deplete the magma of Mg,
Ca. Cr and Ni. Plagioclase fractionation would remove AI203, CaO and Sr from the system. TiO2, K20,
P20s and Ba are strongly incompatible with respect to plagioclase and clinopyroxene. Therefore, con-
centrations of these elements would increase as differentiation proceeded. The linear and slightly cur-
vilinear trends on Figure 5 indicate that either the fractionating assemblage remained fairly constant in its
chemical composition or that magma mixing or assimilation has occurred. The following discussion sup-
ports the former suggestion. Criteria for either magma mixing or assimilation having occurred, such as
evidence of end-member magmas, xenoliths, high alkali contents or chemical trends that do not fit a
reasonable fractionation model, are not present in the Florida data.
In an attempt to quantify the fractionation assemblage as well as the percent crystallization required to
produce the differentiation pattern of the Florida tholeiite, the following linear algebraic expression of
Weigand and Ragland (1970) was applied:

Y = (Z NX/100) 100/100-N
X = composition of accumulated crystals
where: Y = composition of residual liquid or daughter
Z = composition of the parental magma
N = percent accumulation

Values of X can be calculated by iterating values of N, with Y and Z known. Parent and daughter
(residual) magma compositions (Table 7) were determined by computing linear and quadratic regres-
sions of all the elements versus the MI. MI values for FGS 1 and FGS 5 were used as "anchors" to deter-
mine these compositions by extrapolation from the curve parallel to the MI axis (x-axis). Correlation coef-
ficients were used to determine whether the data are best represented by a linear or second-order
polynomial curve fit.
Table 7 summarizes the results of the fractionation model for a range of 60 to 80 percent accumulation
using the calculated parent and daughter magmas. An ideal solution is achieved when the incompatible

Table 7. Petrogenetic model for Florida tholeiite showing calculated compositions and nor-
mative mineralogy. See Table 3 for explanation of Norm abbreviations.

WEIGHT PERCENT ACCUMULATION (N)
PERCENT DAUGHTER PARENT 60 | 65 70 75 80

S102
T102
TIO2
Al203
Fe203*
MnO
MgO
CaO
Na2O
KaO
P205

PPM

Ba
Cu
NI
Rb
Sr
V
Y
Zn
Zr

MI

WEIGHT
PERCENT
NORMS

AB
AN
DI
HY
OL
MT
IL

53.4
2.12
12.9
16.2
0.19
2.12
6.91
2.72
1.71
0.36

321
290
12
50
148
300
52
171
199

88

50.5
0.73
13.6
11.1
0.20
7.73
11.5
2.08
0.10
0.06

95
85
66
7
111
248
28
88
63

59

48.5
-0.21
14.1
7.7
0.20
11.5
14.6
1.64
-0.98
-0.15

-56
-52
102
-22
86
213
12
33
-28

40

14.2
31.8
33.9
3.62
15.4
1.15
0

48.9
-0.03
14.0
8.4
0.20
10.7
14.0
1.73
-0.78
-0.11

-27
-25
95
-16
91
220
15
43
-10

44

15.1
31.2
32.2
8.6
11.7
1.25
0

49.2
0.12
13.9
8.9
0.19
10.1
13.5
1.80
-0.60
-0.08

-2
-3
89
-11
95
226
18
52
5

47

15.7
30.7
30.8
12.8
8.43
1.33
0.23

49.5
0.26
13.9
9.4
0.19
9.6
13.1
1.86
-0.45
-0.05

20
16
84
-7
99
230
20
60
18

49

16.2
30.4
29.4
16.3
5.8
1.41
0.50

49.7
0.37
13.8
9.8
0.19
9.1
12.7
1.91
-0.31
-0.02

38
34
79
-4
102
235
22
67
29

52

16.7
29.9
28.3
19.9
2.95
1.47
0.72

elements reach positive values with increasing values for N. With the exception of K20, P206 and Rb, ac-
ceptable values of N range from 70 to 75 percent (Table 7). The negative values for K20, P205 and Rb are
problematic. K20 and Rb may have been selectively added to the magma from the country rock ("wall
rock reaction" of Green and Ringwood, 1967). Enrichment of K20 during alteration of diabase in the
Culpeper Basin of Virginia has been observed by Ragland and Arthur (1987). Another related possibility
is that alteration of the diabase resulted in scatter among the data (P20s and Rb) which yielded a regres-
sion not representative of fractionation, thus the compositions for those elements used in the model may
be incorrect.
Using TiO2, Ba, Cu and Zr for final criteria, the model gives a value of 70 to 75 percent accumulation of
fractionated crystals in order to account for the observed variations in Florida tholeiite chemistry. TiO2
and Zr become positive between N = 65 and 70 percent, whereas Ba and Cu values become positive
between N = 70 to 75 percent. Normative mineralogy of the assemblage at this range in percent ac-
cumulation includes approximately 7 percent olivine, 46.5 percent plagioclase (AN= 66), 44.7 percent
pyroxene and 1.5 to 2 percent Fe-Ti oxides. If samples FGS 1 and 5 had been chosen to represent
daughter and parent magmas, respectively, rather than relying on regression compositions, at N = 75
percent, P20s and Rb also become positive. In either case, the modeled accumulation assemblage ac-
counts for all compatible element variations.
Weigand and Ragland (1970) and Cummins (1987) report lower values for percent accumulation (N =
65) with respect to differentiation of the ENA diabase suite. This provides further evidence that the
Florida tholeiite is more evolved than that of the average ENA suite. However, the Florida tholeiite model
assumes that the calculated composition at MI = 59 represents the parental magma for the suite. If the
true parental magma is more primitive, that is, higher concentrations of Ni, Ca and a lower MI, the values
for N would be lower.
Diabase petrogenetic studies occasionally apply the Ti-Zr-Y discrimination diagram of Pearce and
Cann (1973) to determine paleotectonic environments. On this diagram (Figure 6), the Florida data plot
within the calc-alkaline, low-potassium tholeiite and ocean floor basalt fields. This suggests both a con-
verging plate margin and a mid-ocean ridge affinity. Philpotts (1985) has shown a considerably larger set
of ENA diabase data to fall within these fields. As indicated by Philpotts (1985), use of "Pearce and Cann
(1973) diagrams" as well as other tectonic discrimination diagrams for ENA diabase and basalt may be
inappropriate. Similar conclusions have been drawn by Gottfried et al. (1973), Cummins (1987) and Sol
(1987) for ENA diabase. Alternatively, the data may suggest that these magmas were generated from
multiple source regions (Philpotts, 1985), one of which may be subduction related (Pegram, 1983).

ASSOCIATION

Similar differentiation patterns and fractionation assemblages, as well as proximity and age, suggest
that the Florida tholeiite is part of the ENA tholeiitic suite. In this section, possible genetic associations
between magmas that are considered proximal to Florida prior to Mesozoic rifting and sea-floor
spreading are discussed. Also, a more detailed comparison of the ENA tholeiitic suite to the Florida
tholeiite is presented.
Figure 7, modified from Van der Voo et al. (1976), shows the positions of northwest Africa and north-
east South America relative to southeastern North America during the early Mesozoic. This figure is
presented only to show the geographic relationship of these plates during the emplacement of Mesozoic
tholeiitic magmas. Geochemical studies of Early Mesozoic tholeiites from these continents include the
following:

Morocco Bertrand et al., 1982
Surinam Choudhuri, 1978
Liberia Testa, 1978

Ti/100

Zr

3Y

Figure 6. Florida Geological Survey samples plotted on a Ti/100 3Y Zr discrimination diagram
(Pearce and Cann, 1973). A low-K20 tholeiites; B ocean floor basalts, low K20 tholeiites
and calc-alkaline basalts; C calc-alkaline basalts; and D intra-plate basalts.

NORTHWEST
AFRICA

SURINAM

1600 KILOMETERS
I

1000 MILES

Figure 7. Early Mesozoic pre-rift configuration of the continents. Modified from Van der Voo et al.,
(1976).

SOUTHEAST
NORTH AMERICA

MOROCCO

NORTHEAST
SOUTH AMERICA

LIBERIA

800

500

0
L117b

90.0
*

80.0 SURINAM

w
V

." HF Q
Z 70.0 .\

60.0 /
..- .*'" ."-MOROCCO

I I I I
1.0 2.0 3.0 4.0

T102 (wt%)

Figure 8. Mafic index plotted versus TiO2 (weight percent) showing fields of Georgia, Surinam,
Morocco and Liberia tholeiites. Florida data plotted as closed circles. Data referenced in
text. Solid diamonds denote average magma compositions from Weigand and Ragland
(1970).

2.0

0

1.5
MgO (
0

HTQ
HFQ

1.0

9 LTQ

3.0 4.0 5.0 6.0 7.0 8.0

MgO (wt.%)

Figure 9a. Comparison plot of T102 versus MgO (both in weight percent) for Florida tholelite. Georgia
field represents dike and sheet data referenced in text. IEE and IED trends from Puffer and
Philpotts (1988). Solid diamonds denote average magma compositions from Weigand and
Ragland (1970).

4.0

3.0
SURINAM

0 2.0

MORocco
1.0

4.0 6.0 8.0 10.0 12.0

MgO (wt.%)

Figure 9b. Comparison plot of TiO2 versus MgO (both in weight percent) for Florida Surinam, Liberia
and Morocco tholeiites. Fields or linear regressions are shown rather than raw data for
simplicity. lED and IEE trends from Puffer and Philpotts (1987). Other data referenced in
text.

If any of the magmas from these areas are genetically associated with the Florida magma, one of two
trends would be observed on a plot of MI versus TiO2. Either the observed trend could be explained by
the same parental melt but a different differentiation path (slope) from that of Florida or the trend would
be identical to the Florida trend. The data plotted on Figure 8 suggest that there may be a parental rela-
tionship between the Florida and Liberia suites. There appears to be no relationship between these
suites and the Surinam or Morocco diabase. Figure 8 also shows that the Florida tholelite and the
Georgia diabase dikes (Weigand, 1970; Gottfried et al., 1986) and sheets (Chowns and Williams, 1983)
are part of the same differentiation trend.
Rather than utilizing MI versus TiO2 variations as a means of comparing magma chemistry, some
studies have applied the oxide-oxide plot of MgO versus TiO2. The incompatible element enriched (IEE)
and incompatible element depleted (IED) trends reported by Puffer and Philpotts (1988) were delineated
on such a diagram. Their two trends consist of several average compositions of northeast United States
basalts and diabase, such as the York Haven Basalt (IEE) and the Sanders Basalt (lED). The MgO-TIO2
variations for Georgia, Surinam, Morocco and Liberia data are shown as either linear regressions or
fields representing data for which a regression is misleading or inappropriate (Figures 9a and 9b). Also,
in order to avoid a "noisy" and possibly misleading representation of data, the trends are shown on two
scales: Figure 9a shows the Florida data compared to suites with relatively low concentrations and
ranges of MgO and TiO2; Figure 9b has expanded axes which allow the Liberia and Surinam fields and
the Morocco trend to be shown in their entirety. Puffer and Philpotts' (1988) IEE and IED trends are
shown for comparison. Evaluation of the trends suggests (1) Florida, Georgia and IED diabase and
basalts may be co-genetic; (2) a genetic relationship may exist between the IEE and Morocco rocks; (3)
Liberian diabase has undergone differentiation (i.e., decreasing MgO content) from a parental-
composition that is approximately chemically equivalent to that of the Florida, Georgia and IED magmas;
and (4) the Surinam data show no trend and are probably unrelated.
Numerous studies, such as Gottfried et al. (1983) and Pearce and Cann (1973), have demonstrated
that bivariate plots of incompatible elements can discriminate between magma types because parental
and source magma compositions are sensitive to incompatible element ratios. Constant ratios on such a
diagram would plot as an array of trends that intersect the origin, thus indicating that the elements are
equally incompatible with respect to the evolving magmas. Figure 10 is a plot of Ti/100 versus Zr for the
Florida, Georgia, Morocco and Surinam tholeiite and average compositions of Weigand and Ragland's
(1970) three quartz-normative magma types. A comparison of lines regressed through these data reaf-
firms a prior conclusion drawn from Figures 8 and 9, namely that the Florida tholeiite is not genetically
related to the Morocco and Surinam magma systems. Unfortunately, no trace element data are available
for the Liberian suite. Assuming that the Florida samples represent a single magmatic suite, Figure 10
suggests that the Georgia tholeiitic dikes had a slightly different source composition than the Florida
diabase. Note, however, that three Florida samples (FGS 2, 5 and 11) plot on the Georgia trend. This
scatter may be due to clinopyroxene and/or ilmenite-magnetite fractionation, or the presence of
clinopyroxene phenocrysts.
For comparison, the IEE and IED trends (Puffer and Philpotts, 1988) are also plotted on Figure 10.
Again, the Florida trend is almost identical to the IED trend, which suggests that the two suites share the
same (or chemically identical) source and style of differentiation. The negative slope of the IEE trend sug-
gests that the suite has undergone strong fractionation of a Ti-enriched phase, probably ilmenite. TiO2
enrichment in a parent magma may be due to partial melting of the source at different depths. Increasing
depths of basaltic magma generation leads to an increase in TiO2 content (MacGregor, 1969).
Isotopic studies and further geochemical investigation of early Mesozoic tholelites in northwest Africa
(e.g., Mauritania, Senegal) and northeast South America (e.g., French Guiana, Venezuela) are needed in
order to define better the relationships between these magmas and the Florida tholeiitic suite. Additional
chemical analyses of the subsurface tholeiites in the southeastern United States are needed in order to
determine whether the relationships observed between the olivine- and quartz-normative magmas far-
ther north can be applied to the tholeiite in the Florida-Georgia region. The relationship between the
Mesozoic mafic and felsic rocks in the Florida basement requires further study to enable the develop-
ment of a more comprehensive petrogenetic model of the Mesozoic igneous rocks of Florida.

200.0-

160.0-

N

- 4

'/-

K "_____

I
50.0

10I
100.0

15.
150.0

20.0
200.0

25.0
250.0

Zr (ppm)

Figure 10. Ti/100 (ppm) plotted versus Zr (ppm) showing Florida tholeiitic trend. Linear regressions
through data from Surinam, Morocco, Georgia (dikes only) and northeastern United States
(IED and IEE, see text) are also shown. Data referenced in text. Solid diamonds denote
average magma compositions from Weigand and Ragland (1970).

FLORIDA, r=.93, n=14
n= GEORGIA, r=.88, n=9
MOROCCO, r=.80, n=16
SURINAM, r=.62, n=6
IEE, r=-.68, n=10
lED, r=.91, n=7

E
Q.
O.
0
O
ip

120.0-

80.0-

40.0-

- ~C- -- I I

Conclusions

1) Early Mesozoic tholeiite from the subsurface of Florida plots as a trend from the low-TiO2 quartz-
normative (LTQ) through the high-Fe20O quartz-normative (HFQ) magma types of Weigand and Ragland
(1970) and is more differentiated than the average eastern North America diabase suite.
2) Seventy to 75 percent accumulation of a fractionation assemblage containing plagioclase (46 percent),
pyroxene (45 percent), olivine (7 percent) and Fe-Ti oxides (1.5 to 2 percent) accounts for the differentia-
tion patterns observed in the Florida quartz-normative magma. Petrographic analysis confirms this
model in that phenocrysts of plagioclase, clinopyroxene and iddingsite (after olivine?) are observed
either in this study or in previous investigations.
3) Major element data suggest that the Florida, Georgia, Liberia and northeastern United States incom-
patible element depleted (lED Puffer and Philpotts, 1988) tholeiite may have had the same parental
magma or different parental magmas of the same composition. Ti-Zr ratios possibly indicate that the
Surinam, Morocco, Georgia and northeastern United States incompatible element enriched (IEE Puffer
and Philpotts, 1988) quartz-normative tholeiites had different source compositions than the Florida and
IED tholeiites. Also, the IED and Florida tholeiite may have been derived from the same parental and
source compositions.
4) MgO-TiO2 systematics indicate that the Florida, Georgia and IED tholeiites are co-genetic. The same
relationship may exist between the IEE and Morocco tholeiites.
5) Available data suggest that there is no apparent systematic geochemical variation in the Florida
tholeiite with respect to geography.

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Green, D.H., and Ringwood, A.E., 1967, The genesis of basaltic magmas: Contributions to Mineralogy
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America: Contributions to Mineralogy and Petrology, v. 29, p. 195-214.

Appendix 1. Petro

DEGREE OF
SAMPLE GRAIN SIZE ALTERATION

graphy of Florida tholelite analyzed in this report.

ALTERATION/-
ACCESSORY
PHENOCRYSTS GROUNDMASS MINERALS

TEXTURE

FGS 1' Medium

FGS 2

Coarse,

PL>CPX>OP>.GR

Moderate-High Intergranular.
Porphyritic

Moderate

FOS 3" Medium-Coarse Fresh

Subophytic,
Porphyrilic

Subophylic,
Porphyritic

PL + CPX(<5%) PL >CPX OPPGR

CPX + PL (S5%) PL>CPX OPmOGR

Fine

Medium

Moderate-High Trachytic. Ophlmottled
Vesicular, Porphyritic

Fresh

PL (<1%)

Isogranular, Trachytic,
Equlgranular

Fine Moderate Isogranular, Trachytic,
Porphyritic

Mediurn-Coarse Moderate-High Intergranular,
Equigranular

Medium Moderate Intergranular,
Equigranular

Medium

FOS 10 Medium

FOS t1 Mediumr

Moderate Intergranular to
Isogranular.
Equigranular

Fresh

Intergranular.
Spherulitic,
Equlgranular

Fresh Isogranular to
Intergranular.
Equigranular

FGS 12-14' Fine-Medium Moderate

Isogranular to
Intergranular,
Porphyritic

PL>CPXP.OP

PL CPX>OP

PL + CPX (<1%) PL> CPX >OP

PL>CPX>OP

PL>CPX>OP>GR

PL>CPX>-OP

PL>CPXPOP

PL>CPX>OP

PL -CPX>OP

CH, CT. ZT, SER Vesicles filled with
microcrystalllne zeolite

BI

AP. CH. HB. ZT

AP, BI, CH, SER,
ZT

AP, BI, CH, SER

BI, CH

BI, CH

Skeletal opaques

Zeolite filled vein

AP, CH, SER

Gram sizes are Fine IC 0 mnm). Medium (>0 1 mm, <1 0 mm) and Coarse (21 0 mm). Abbreviations for major mineral constituents are PL Plagioclase, CPX Clinopyroxene (Augite), OP -
Opaques. (Fe Ti Oxides). OR Granophyre (nlergrowths of Quartz and K-Feldspar). Abbreviations for alteration and accessory minerals include: AP Apatite, BI Biotite, CH Chlorite, CT
Calite. HB Hornblende (iiralite? in the alteration of cllnopyroxene). SER Sericie, ZT Zeolites; indicates that thin-section does not exactly represent sampled interval on Table 5.

COMMENTS

AP, 81, CH, HB,
SER

AP. BI, CH. HB,
SER

AP. CH, HB

FOS 4

FOS 5

FOS 6

FOS I

FOS 8

FOS 9

PL I(1%)

Analytical accuracy (observed versus expected values) and precision
variation) for geochemical data. ND not determined.

(coefficient of

USGS-W-2

USGS-BCR-1

Observed

54.6
2.17
14.0
13.3
0.19
3.50
7.75
3.24
1.95
0.39

748
[253
29
12
40
325
330
39
115
212

ExDected

675
270]**
18
16
47
330
399
37
120
190

Coefficient
of Variation

**Values for Cr in
DNC-1.

USGS-BCR-1 are below detection Bracketed values are from analyses of USGS-

Appendix 2.

Weight
Percent

Observed

SiO2
TiO2
AI203
FeOa3*
MnO
MgO
CaO
Na2O
K20
P205

52.1
1.05
15.6
11.1
0.17
6.48
10.8
ND
0.68
0.17

Expected

52.1
1.06
15.5
10.8
0.17
6.37
10.8
2.20
0.63
0.14

PPM

54.89
2.22
13.7
13.5
0.19
3.49
6.98
3.29
1.68
0.33

0.49
1.49
0.22
0.53
0.79
0.72
0.67
0.34
1.14
8.69

Ba
Cr
Cu
Ni
Rb
Sr
V
Y
Zn
Zr

175
73
105
70
15
193
248
29
78
114

174
92
106.
70
21
192
259
23
80
100

1.06
3.20
19.3
3.67
16.1
2.78
1.12
18.5
1.99
5.32

Observed of Variation

PART II AN OVERVIEW OF FLORIDA BASEMENT GEOLOGY

Discussion

Basement rocks in Florida have been variably defined to include rocks which are pre-Mesozoic (Applin,
1951), pre-Cretaceous (Milton and Grasty, 1969; Bass, 1969), early Paleozoic (Milton, 1972) and sub-
Zuni (Barnett, 1975). The variation in definition of the Florida basement is due to the numerous uses of
the term "basement." Basement may be defined as structural, stratigraphic, seismic or petrologic. Re-
cent literature has generally accepted the pre-Cretaceous surface as an appropriate upper limit of the
Florida basement (Klitgord et al., 1984; and Dallmeyer et al., 1987). In this context, "basement" refers to
stratigraphic basement below a regionally recognizable and tectonically significant unconformity. This
context is considered to be the most appropriate. The unconformity separates pre- to syn-rift rocks from
overlying sedimentary rocks deposited during post-rift passive margin sedimentation.
In Florida, the oldest rocks overlying this unconformity are Middle Jurassic in age (Sigsby, 1976;
Braunstein et al., 1988). Thus, "pre-Cretaceous" does not accurately constrain the basement (post-rift
unconformity) surface. In addition, existing pre-Cretaceous maps (e.g., Dallmeyer et. al., 1987) are
technically mislabled because the maps do not include Jurassic sedimentary units. Specifically, the
Jurassic Werner Anhydrite, Louann Salt, Norphlet Sandstone, Smackover Formation, Haynesville For-
mation and the Cotton Valley Group of the central and western Florida panhandle and the Wood River
Formation of south Florida are not included in any "pre-Cretaceous" basement map mentioned above.
Chowns and Williams (1983) use both the terms "pre-Cretaceous" and "pre-Upper Jurassic" in
reference to basement rocks in their paper. In order to alleviate these problems, the present study refers
to the Florida basement surface as pre-Middle Jurassic. This age designation more accurately constrains
the Mesozoic post-rift unconformity in the subsurface of Florida.
The distribution of pre-Middle Jurassic basement lithologies and tectonic features in the Florida base-
ment are shown in Figures 11 and 12. Based upon data from previous studies (Applin, 1951; Milton and
Grasty, 1969; Bass, 1969), as well as more recently reported radiometric age and petrographic data,
Barnett (1975) recognized six basement provinces in the subsurface of Florida: 1) a province consisting
of Paleozoic and older igneous rocks in the panhandle; 2) a tilted crustal block of Paleozoic sediments in
the central panhandle; 3) a northeast trending graben filled with Triassic red beds in the eastern panhan-
dle; 4) an early to middle Paleozoic sedimentary province overlying the Peninsular Arch; 5) an east-
central triangular shaped region of upper Precambrian-Lower Cambrian metamorphic and felsic igneous
rocks; and 6) a southern Triassic-Jurassic volcanic province.
Since Barnett's (1975) study, improved well coverage resulting in more control points, as well as new
radiometric data have led to more recent Florida Basement maps (Dallmeyer et al., 1987; Dallmeyer,
1987). The generalized lithologic map (Figure 11, this report) is the result of an extensive literature
review. It is beyond the scope of this study, however, to re-evaluate cuttings for which more than one in-
terpretation exists in the literature. Areas designated by question marks on Figure 11 are those for which
there are conflicting descriptions or lack of sufficient data. Other differences between this and previous
basement maps are due to: 1) varying definitions of "basement," 2) misidentification of samples (e.g.,
labeling a weathered (oxidized) basalt as a rhyolite (G. Winston, 1987, personal communication),
3) previous studies describing well bottom samples as basement surface, when in fact the samples are
overlain by other basement rocks (e.g., basalt overlying metamorphic rock in St. Lucie County). All un-
published radiometric data discussed in this section are available at the Florida Geological Survey.
The existence of the different names for individual structural features (or similar names for different
features) in north Florida is a common problem in the literature. For example, the rift-related Chat-
tahoochee Arch is commonly confused with the overlying Early Tertiary Chattahoochee Anticline; the lat-
ter has also been called the Decatur Arch (Puri and Vernon, 1964). Another pertinent example is the
Apalachicola Embayment. Fourteen names have been assigned to this feature, including the South
Georgia Rift (Daniels et al., 1983), the Tallahassee Graben (Smith, 1983) and 11 other summarized in
Table 7 of Schmidt (1984).

Nomenclature of lithotectonic features discussed in this report was chosen based on the following
criteria (when applicable): 1) the names accurately describe the location of the feature, named after
towns centered on or near the feature's axis; 2) the axis, center or extent of the more regional features is
well defined by the nomenclature (e.g., Peninsular Arch and South Florida basin); 3) the names are con-
sistent for genetically related Mesozoic features in the region (e.g., the Conecuh and Apalachicola Em-
bayments; and 4) the nomenclature is well established in state and federal literature as well as in the oil
and gas industry. Admittedly, revision of some of the nomenclature would give a more accurate lithotec-
tonic description of these features. For example, the "embayments" might be better defined if called
"grabens." However, due to the need for consistency and to avoid further confusion by adding to the list,
no new names are introduced. The Florida basement nomenclature used in this report should be used in
subsequent publications. All structural features shown on the Florida basement map (Figure 12) are
discussed in the following text from northwest to southeast.
In the Florida panhandle, the Conecuh Embayment, the Chattahoochee Arch and the Apalachicola
Embayment are thought to be a graben-horst-graben sequence formed during Mesozoic rifting (Miller,
1982). These grabens contain Triassic Newark Group equivalent sediments (Eagle Mills Formation) and
Jurassic sedimentary rocks interlayered or cut by basalts and diabase. Contact metamorphic aureoles
are associated with the intrusions (Milton, 1972). In the above context, the horst is represented by the
Chattahoochee Arch, which is an uplifted block consisting of Triassic and Paleozoic sediments overlying
an Upper Precambrian Lower Cambrian igneous terrane. Arden (1974) quantified the extent of
Paleozoic sediments in the area with seismic data, identified the block as the western limit of the north-
west trending Paleozoic Suwannee basin and suggested the presence of a thick Triassic section in the
uplifted block. More recently, however, Arden (1987, written communication) notes that most of the
sediments near the arch are Paleozoic (based on fossil evidence) rather than the uppermost part being
predominantly Triassic, as previously reported (Arden, 1974). In contrast, lithologic descriptions and
well-log interpretations suggest there is no Traissic in this area (G. Winston, personal communication,
1988).
The Suwannee basin sediments generally consist of Ordovician quartzitic sandstones and Silurian to
Devonian black shales and siltstones, some of which are red and may be confused with Triassic red
beds. Paleontological evidence constrains the age of these Paleozoic rocks and suggest an early
Paleozoic connection of Florida to Africa and South America (Gondwana) (Cramer, 1973; Pojeta et al.,
1976). More recent paleomagnetic (Opdyke et al., 1987) and geochronologic evidence (Opdyke et al.,
1987; Dallmeyer, 1987) support this conclusion.
Felsic igneous (and metamorphic ?) rocks underlying the Suwannee sediments are directly below the
top of the basement surface in the Florida panhandle. These crystalline rocks may belong to the same
terrane as that of central Florida (Chowns and Williams, 1983). An unpublished K-Ar (feldspar) age deter-
mination of 709 25 Ma from a granodiorite in Gulf County (Earth Resource Consultants, Inc., 1981;
W-12509, P-746), however, suggests that the panhandle igneous complex may be older than that of cen-
tral Florida.
The northeast-trending Apalachicola Embayment lies east of the Chattahoochee Arch. Corehole data
indicate that the Apalachicola Embayment contains secondary horst blocks (Barnett, 1975). The Triassic
sediments located east of the Apalachicola Embayment (those centered on Taylor County; Barnett, 1975)
may be erosional remnants of a separate basin or the preserved eastern extension of the Embayment
separated by a secondary horst block. In contrast, if the red beds beneath Taylor County are Paleozoic
rather than Mesozoic as suggested by Winston (1987, personal communication) then they represent part
of the Suwannee basin.
Palynology of sedimentary rocks (written communication, D.L. Martin, Sohio, 1985) and radiometric
data from basalts (Table 1) sampled from the Gainesville 707 offshore corehole (Figure 1, corehole loca-
tion number 3) indicate that the Triassic graben(?) of the Apalachicola Embayment and/or Taylor County
Mesozoic(?) sediments extend at least 40 miles into the Gulf of Mexico. Ironically, overlying the basalts at
12,440 feet in this corehole, rhyolitic cuttings yield a Rb-Sr whole rock age of 576 20 Ma (Sohio, 1986).
These have been interpreted to represent coarse plastic deposits "whose source is an uppermost
Precambrian to lowest Cambrian terrane of acid volcanics and fine grained granites" (written com-

i

f
C...'

MA-

EXPLANATION
Triassic red-beds and
diabase intrusions
Early to Middle Mesozoic hypabyssal
and extrusive mafic rocks
Ordoviclan-Devonlan sedimentary rocks
Late Precambrian-Early Cambrian
felsic intrusive rocks
Late Precambrian-Early Cambrian
felsic extrusive rocks

Approximate contact
Denotes areas for which there are conflicting
descriptions or a lack of data

0 25 50 MILES
0 40 80 KILOMETERS
0 40 80 KILOMETERS

4^
%#*0.0 40 '
43 401W

Figure 11. Lithology of the pre-Middle Jurassic Florida basement surface.

BASIN

It"
Ml

EXPLANATION

+ Synclinal axis

+ Anticlinal axis

. Approximate basin limits

0 25 50 MILES

0 40 80 KILOMETERS
0 40 80 KILOMETERS

4o '*

Figure 12. Florida basement pre-Middle Jurassic tectonic features.

munication, A.L. Odom and R. Taylor, Sohio, 1986). An alternative data interpretation suggests that the
aforementioned Triassic section is Paleozoic (G. Winston, personal communication, 1988).
The Apalachicola Embayment and smaller north Florida basins are successor basins within the
Suwannee basin (Figure 12). On a more regional scale, the Apalachicola Embayment is the southwest
extension of the larger South Georgia basin (Chowns and Williams, 1983). The eastern portion of the
South Georgia basin consists of the Southeast Georgia Embayment. These two embayments are
separated by the Suwannee Saddle, which is a northwestern extension of the Peninsular Arch. The
Peninsular Arch is a positive feature containing upper Precambrian-Lower Cambrian continental crust
overlain by Suwannee basin sediments. Intrusions of Mesozoic diabase as well as basalt flows are
located within the Suwannee Basin sediments.
The southeastern subcrop limit of the Suwannee basin is bounded by a central Florida igneous com-
plex. Barnett (1975) has subdivided the igneous terrane into a northern felsic volcanic and southern felsic
to intermediate plutonic province, the latter of which is termed the Osceola Granite (Chowns and
Williams, 1983). Radiometric data indicate that the Osceola Granite is Middle Cambrian in age (approx.
527 Ma, Bass, 1969; 527-534 Ma, Dallmeyer et al., 1987). Both Chowns and Williams (1983) and
Dallmeyer et al. (1987) propose that these older crystalline basement rocks are part of the Pan-African
Rokelide fold belt. A core from St. Lucie County (Figure 1, corehole location number 31), south of the
Osceola Granite, is reported to contain Pan-African metamorphic rocks overlain by a felsic igneous se-
quence and Mesozoic (?) basalt (Bass, 1969; Chowns and Williams, 1983). Bass (1969) reports an ap-
proximate age of 530 Ma (Rb-Sr, biotite) for dioritic gneiss in this core.
The South Florida basin shown on Figure 12 is a Mesozoic stratigraphically defined basin centered in
the Gulf of Mexico. The portion of the basin located on Peninsular Florida is approximately the nor-
theastern third of the entire basin. Within this portion of the basin, Jurassic and younger sediments
overlie a predominantly mafic volcanic basement (Winston, 1971; Barnett, 1975). Cuttings from a deep
oil test well in Collier County (Exxon, W-15095, P-1042), however, reveal felsic igneous rock directly
below the top of the basement surface at the depth of approximately 17,000 feet. An unpublished K-Ar,
whole rock age determination from the cuttings suggests Middle Jurassic emplacement (164 7 Ma,
Amoco, 1985). Also in Collier County, a "rhyolite porphyry" in Bass well No. 12-2 (W-12838, P-778) has
been dated at 189 5 Ma (Rb-Sr whole rock, Shell Oil, 1978). Radiometric dating of basalts in the basin
indicates that their emplacement was during the Early to Middle Jurassic (Table 1). Note, however, that
caution should be used when interpreting any of these data (see "Age" section in Part One of this
report).
Since the early comprehensive works of Applin (1951) and Barnett (1975), numerous studies have
focused on geophysical, radiometric, paleontologic, petrologic and tectonic aspects of the deep sub-
surface of Florida. Although new data and theories arise, several unanswered questions and occasional
conflicting interpretations still exist. Additional work in all of the above disciplines is needed in order to
further refine our knowledge of the Florida Basement.

REFERENCES

Applin, P. L., 1951, Preliminary report on buried pre-Mesozoic rocks in Florida and adjacent states: U.S.
Geological Survey Circular 91, 28p.
Arden, D. D., Jr., 1974, A geophysical profile in the Suwannee Basin, northwestern Florida, in Stafford, L.
P. (ed.) Symposium on the petroleum geology of the Georgia Coastal Plain, Georgia Geological
Survey Bulletin 87, p. 111-122.
Barnett, R. S., 1975, Basement structure of Florida and its tectonic implications: Gulf Coast Association
of Geological Societies Transactions, v. 25, p. 122-142.
Bass, M. N., 1969, Petrography and ages of crystalline rocks of Florida some extrapolations: American
Association of Petroleum Geologists Memoir no. 11, p. 283-310.
Braunstein, J., Huddlestun, P. and Biel, R. (eds.), 1988, Gulf coast region: correlation of stratigraphic
units in North America (COSUNA) Project, Tulsa, American Association of Petroleum Geologists.
Chowns, T. M., and Williams, C. T., 1983, Pre-Cretaceous rocks beneath the Georgia Coastal Plain-
regional implications: in Gohn, G. S. (ed.), Studies related to the Charleston, South Carolina, earth-
quake of 1886 tectonics and seismicity: U. S. Geological Survey Professional Paper 1313-L, 42 p.
Cramer, F. H., 1973, Middle and Upper Silurian chitinozoan succession in Florida subsurface: Journal of
Paleontology, V. 47, no. 2, p. 278-288.
Dallmeyer, R.D., 1987, 40Ar/39Ar age in detrital muscovite within Lower Ordovician sandstone in the
coastal plain basement of Florida: Implications for west Africa terrane linkages: Geology, v. 15, p.
998-1001.
Dallmeyer, R. D., Caen-Vachette, M., and Villeneuve, M., 1987, Emplacement age of the post-tectonic
granites in southern Guinea (West Africa) and the peninsular Florida subsurface: Implications for
origins of southern Appalachian exotic terranes: Geological Society of America Bulletin, v. 99, p.
87-93.
Daniels, D. L., Zeitz, I., and Popenoe, P., 1983, Distribution of subsurface lower Mesozoic rocks in the
southeastern United States as interpreted from regional aeromagnetic and gravity maps, in Gohn,
G. S. (ed.), Studies related to the Charleston, South Carolina, earthquake of 1886 -tectonics and
seismicity: U. S. Geological Survey Professional Paper 1313-K, 24 p.
Klitgord, K. M., Popenoe, P., and Schouten, H., 1984, Florida: A Jurassic transform plate boundary: Jour-
nal of Geophysical Research, v. 89, p. 7753-7772.
Miller, J. A., 1982, Structural control of Jurassic sedimentation in Alabama and Florida: American
Association of Petrology Geologists Bulletin, v. 66, p. 1289-1301.
Milton, C., 1972, Igneous and metamorphic basement rocks of Florida: Florida Bureau of Geology
Bulletin 55, 125 p.
Milton, C., and Grasty, R., 1969, "Basement" rocks of Florida and Georgia: American Association of
Petroleum Geologists Bulletin, v. 53, no. 12, p. 2483-2493.
Opdyke, ND., Jones, D.S., MacFadden, B.J., Smith, D.L., Mueller, P.A., and Shuster, R.D., 1987,
Florida as an exotic terrane: Paleomagnetic and geochronologic investigation of lower Paleozoic
rocks from the subsurface of Florida: Geology, v. 15, p. 900-903.

Pojeta, J., Jr., Kriz, J., and Berdan, J. M., 1976, Silurian-Devonian pelecypods and Paleozoic
stratigraphy of sub-surface rocks in Florida and Georgia and related Silurian pelecypods from
Bolivia and Turkey: U. S. Geological Survey Professional Paper 879, 32 p.

Puri, H. S., and Vernon, R. 0., 1964, Summary of the geology of Florida and a guidebook to the classic
exposures: Florida Geological Survey Special Publication 5, revised, 312 p.
Schmidt, W., 1984, Neogene stratigraphy and geologic history of the Apalachicola Embayment, Florida:
Florida Geological Survey Bulletin 58, 146 p.
Sigsby, R. J., 1976, Paleoenvironmental analysis of the Big Escambia Creek-Jay-Blackjack Creek Field
area: Gulf Coast Association of Geological Societies, v. 26, p. 258-278.
Smith, D. M., 1983, Basement model for the panhandle of Florida: Gulf Coast Association of Geological
Societies Transactions, v. 33, p. 203-208.
Winston, G. 0., 1971, Regional structure, stratigraphy, and oil possibilities of the South Florida Basin:
Gulf Coast Association of Geological Societies, v. 21, p. 15-29.

.FLORIDA DEPARTMENT OF NATURAL RESOURCES

BUREAU OF GEOLOGY
FLORIDA GEOLOGICAL SURVEY

W
Peter M. Dobbins, Admin. Asst.
Jessie Hawkins, Custodian
Jes -H kn, Custodian

alter Schmidt, Chief
Alison Lewis, Librarian
Sandle Ray, Secretary

GEOLOGICAL INVESTIGATIONS SECTION

Thomas M. Scott, Senior Geologist/Administrator
Jon Arthur, Geologist Jim Jones, Draftsman
Paulette Bond, Geologist Ted Kiper, Draftsman
Ken Campbell, Geologist Jacqueline M. Lloyd, Geologist
CindyC Qller, SeQretary John Morrill, Core Driller
Joel Duncan, Research Asst Albert Phillips, Asst. Driller
Richard Howard Laboratory Tech. Frank Rupert, Geologist
Richard Johnson, Geologist Frank Rush, OPS Lab. Tech.

OFFICE OF MINERAL RESOURCE INVESTIGATIONS
AND
ENVIRONMENTAL GEOLOGY SECTION

J. William Yon, Senior Geologist/Administrator
David Allison, Research Asst. Ron Hoenstine, Geologist
Melissa Doyle, OPS Draftsman Ed Lane, Geologist
Roger Durham, Research Asst. Steve Spencer, Geologist
Mike Weinberg, Research Asst.

OIL AND GAS SECTION

L. David Curry, Administrator
Brenda Brackin, Secretary George Heuler, Research Asst.
Robert Caughey, Prof. Eng. I Barbara McKamey, Secretary
Joan Gruber Seretary Pete Parker, Geologist
Scott Hosklns, Geologist Joan Ragland, Geologist
Charles Tootle, Engineer
:.:. :-: .., :.: .;i.!-:: .. i ::, '-: .- : .
. -.. : : .. . -: . -. .

FLRD GEOLOSk ( IC SUfRiW

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	Front Matter
	Title Page
	Letter of transmittal
	Table of Contents
	List of Tables
	Abstract
	Acknowledgement
	Introduction
	Part I. Petrogenesis of early Mesozoic...
	Part II. An overview of Florida...
	Back Matter
	Copyright

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