7 1 -7 4 3 6

EASTIN, Rene, 1941- , GEOCHRONOLOGY OF THE BASEMENT ROCKS OF THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA.

The Ohio State University, Ph.D., 1970 Geology

University Microfilms, A XEROX Company, Ann Arbor, Michigan GEOCHRONOLOGY OF THE BASEMENT ROCKS OF THE CENTRAL TRANSANTARCTIC MOUNTAINS, ANTARCTICA

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University

By

/ Rene Eastin, B.S., M.S.

The Ohio State University 1970

Approved by

Adviser Department of Geology PLEASE NOTE:

Some pages have small and indistinct type. Filmed as received,

University Microfilms ACKNOWLEDGMENTS

The author is greatly indebted to Professor Gunter Faure who suggested this study and who provided the constructive criticism and guidance necessary for its completion. .Drs. R. L. Bates, R. Fleck, and E. D. Rudolph reviewed the manuscript and their many helpful sug­ gestions are gratefully acknowledged. The samples used in this study were generously supplied from many sources. Dr. D. L. Schmidt, U. S. Geological Survey, provided rocks from the Pensacola Mountains together with much help­ ful information. Dr. A. B. Ford, U. S. Geological Survey, supplied samples from the Thiel Mountains. Dr. M. J. Hibbard, University of Nevada, Reno, and Douglas McLelland helpfully cooperated in allowing the author to obtain a suite of sample of the Nilsen Plateau from their collections. Dr. D. C. Neethling, Geological Survey, Republic of South Africa, sent the author samples from Western Queen Maud Land. N. B. Aughenbaugh, University of Missouri, Rolla, and J. C. Behrendt, U. S. Geological Survey, provided rocks from the Iittlewood Nunataks. The specimens from Bertrab Nunatak were made available by the Instituto Antartico Argentino. Development of the methods of x-ray fluorescent analyses was facilitated by advice from Drs. J. L. Powell, Oberlin College, D. E. Livingston, University of Arizona, H. W. Fairbaim, Massachu­ setts Institute of Technology, and Mr. John Gunner, The Ohio State

i i University. Financial support by an NDEA Title IV Fellowship and by

National Science Foundation Grant No. GA 898X is certainly appreciated.

i i i VITA

July 8 , 1941 Bom — Cleveland, Ohio

1965 B.S., The Ohio State University, Columbus

1965 Teaching Assistant, Department of Geology, The Ohio State University, Columbus

1965- 1968 Title IV NDEA Fellow, Department of Geology, The Ohio State University, Columbus

1966 Geologist, White Pine Copper Co., White Pine, Michigan

1967 M .S., The Ohio State University, Columbus

1967 Research Assistant, Institute of Polar Studies, The Ohio State University, Columbus

1968- 1969 Teaching Assistant, Department of Geology, The Ohio State University, Columbus

1969- ■1970 Research Assistant, Institute of Polar Studies, The Ohio State University, Columbus

1970- Post-doctoral Fellow, Department of Geology, University of Pennsylvania, Philadelphia

PUBLICATIONS

1966, Geochemical Aspects of the Scioto and Olentangy Rivers at Columbus, Ohio; Unpublished M.Sc. Thesis, Department of Geology, The Ohio State U niversity, 105 p. VITA (Continued) with Faure, G ., Jones, L.M., and Christner, M .f 1967, Strontium isotope composition and trace element concentrations in Lake Huron and its principal tributaries; Report No. 2, Laboratory for Isotope Geology and Geochemistry, Water Resources Center and Department of Geology, The Ohio State University, 109 p.

1968, Age of three granitic rocks from the Axel Heiberg - Shackleton Glacier area, Antarctica; in, Faure, G ., e ta l., Geochronology of the Transantarctic Mountains; Report No. 3r, Laboratory for Isotope Geology and Geochemistry, Institute of Polar Studies and Department of Geology, The Ohio State University, pp. 19-28. with Faure, G ., Hill, R.L., and Montigny, R.J.E., 1968, Age Deter­ minations of rocks and minerals from the Transantarctic Mountains; Antarctic J. of U .S., v. Ill, No. 5, pp. 173-175. with Faure, G ., and Shultz, C .H ., 1969, Rb-Sr ages of the littlewood Volcanics and of the acid volcanic rocks of the Neptune Range, Ant­ arctica; Geol. Soc. Amer., Abstracts, N. Central Section. with Faure, G ., 1970, Seasonal variation of the solute content and the 87 88 Sr /Sr ratio of the Olentangy and Scioto Rivers at Columbus, Ohio: Ohio J. Sci., v. 70, No. 3, pp. 170-179. with Faure, G ., in press, Age of the Littlewood Volcanics Coats Land, Antarctica: Jour. Geol.

1970, Age of the Littlewood Volcanics, Coats Land, Antarctica (abstr.): Geol. Soc. Amer., Abstr. with Programs, North-Central Sec., v. 2, No. 6, p. 386.

v CONTENTS Page

ACKNOWLEDGMENTS ...... i l VITA ...... iv TABLES ...... x i FIGURES...... x iv

Chapter I. INTRODUCTION ...... 1 H. THE RUBIDIUM-STRONTIUM WHOLE-ROCK ISOCHRON METHOD OF DATING...... 7 Law of Radioactive D ecay ...... 7 Isochron Diagram ...... 9 Isochron Analysis ...... 10

Sample Preparation for Rb and Sr A n aly sis ...... 15 Pressing pellets for XRF analysis 16

Dissolution of rock powders ...... 16 Mass Spectrometric Methods ...... 17 Sr^/Sr®® ratio analysis ...... 17 Computer processing ...... 19 Analysis of E & A Standard ...... 19 Isotope dilution analysis ...... 22 Sr concentration ...... 22 Rb concentration ...... 25

v i Chapter Spike calibration ...... Contamination ......

Reproducibility ...... X-Ray Fluorescence M ethods ...... Measurement of the Rb/Sr ratio ...... P rin c ip le s ...... Instrument Operating Conditions ...... Counting Procedure ...... Calibration Curve ...... Isochrons by both XRF and ID ..

Computer processing ...... Rb and Sr Concentration by XRF ...... P rin c ip le s ...... XRF and ID com pared ...... Computer processing ...... in. PENSACOLA MOUNTAINS...... Physiography ...... Exploration History ......

Stratigraphy and Structure ...... Patuxent Formation ...... Nelson Limestone ...... Gambacorta Formation ...... Weins Formation ...... Igneous Rocks ...... Chapter Page l D ia b a s e ...... 67 Felsic flows and plugs ...... 67 Hypabyssal porphyry ...... 67 Serpan Granite and Gneiss 67

Laraprophyre d ik es ...... 71 Dufek Intrusion ...... 71 S tru c tu re...... 73 Age Determinations ...... 75 Gambacorta Formation ...... 75 Serpan Granite and Gneiss . , ...... 82 Felsic flows and plugs ...... 88 Patuxent Formation ...... 92 Basalt and Diabase ...... 94

Sum m ary...... 99 IV. THIEL MOUNTAINS...... 104 Introduction ...... 104 General Geology ...... 104 Meta sediments ...... 108

C-H-Q Monzonite Porphyry ...... 108 Biotite Granite and Quartz M o n z o n ite ...... 109 Age Determinations ...... 110 C-H-Q Monzonite Porphyry ...... 110 Biotite Granite and Quartz M o n zo n ite ...... 110

v i i i Chapter Page Sum m ary...... 113 V. NILSEN PIATEAU ...... 117 Introduction ...... 117 General Geology ...... 117 Metasedimentary Rocks ...... 122

Metavolcanic Rocks . .■ ...... 123 Igneous Rocks ...... 124 Lonely Ridge Granodiorite ...... 124 South Quartz M onzonite ...... 124 Cougar Canyon Quartz Monzonite .... 125

North Quartz M onzonite ...... 125 Age D eterm in atio n s ...... 126 Metasedimentary Rocks ...... 126 Metavolcanic Rocks ...... 129 Lonely Ridge Granodiorite ...... 132 South Quartz M onzonite ...... 137

Sum m ary...... 140

VI. COATS LAND...... 142 Introduction ...... 142

Age D eterm ination ...... 145 VII. WESTERN QUEEN MAUD LAND...... 149 Introduction ...... 149 General Geology ...... 151 Age Determ ination ...... 155

Sum m ary...... 158

ix Chapter Page

VIII. CONCLUSIONS...... 160

APPENDIX A...... 170 B. 198

BIBLIOGRAPHY...... 208

x TABLES • Number Page 1. Correlation of Precambrian and Lower Paleozoic 4 Rocks in the Central Transantarctic Mountains

2. Analyses of the Eimer and Amend SrCOg 21 Standard during the period June, 1968 to June, 1970

3. Isotope composition of normal strontium 23

4. Isotope composition of spike strontium 23

5. Isotope composition of normal rubidium 24

6. Isotope composition of spike rubidium 24

7. Calibrations of Sr®** spike solutions 27

8. Calibrations of Rb®^ spike solutions 4 27

9 . Rb and Sr blank analyses 28

10. Comparison of Rb/Sr ratios determined by 45 XRF and isotope dilution

11. Comparison of isochron ages determined 49 by XRF and isotope dilution

12. Comparison of Rb and Sr concentrations in 56 standards as determined by XRF and isotope dilution

13. Stratigraphy of the Gambacorta Formation, 66 Neptune Range

x i Page

Chemical analyses of the Serpan Granite 70 and the Serpan Gneiss, Neptune Range

Chemical analyses of the Gambacorta 72 Formation, Neptune Range

Rb and Sr analytical data for the Gambacorta 76 Formation, Neptune Range

Rb and Sr analytical data for the Serpan 83 Granite and the Serpan Gneiss, Neptune Range

Rb and Sr analytical data for the felsic flows 89 and plugs of the Patuxent Formation, Neptune Range

Rb and Sr analytical data for the Patuxent 93 Formation, Patuxent Range

Rb and Sr analytical data for basalt and diabase 97 from the Patuxent Formation, Neptune Range

Summary of age determinations for the 100 Pensacola Mountains

Published age determinations for the Thiel 106 M ountains

Analytical data for samples from the Thiel 111 M ountains

Summary of age determinations for the 115 Thiel Mountains

Stratigraphy of the Nilsen Plateau, Queen 121 Maud Mountains

x i± Number Page

26. Analytical data for metasedimentary rocks, 127 Nilsen Plateau

27. Analytical data for metavolcanic rocks, 150 Nilsen Plateau

28. Analytical data for the Lonely. Ridge 153 Granodiorite, Nilsen Plateau

29. Analytical data for the South Quartz 138 Monzonite, Nilsen Plateau

30. Summary of age determinations for the 141 Nilsen Plateau, Queen Maud Mountains

31. Analytical data for the Littlewood Volcanics, 146 Coats Land

32. Stratigraphy of Western Queen Maud Land 152

33. Stratigraphy of Ahlmann Ridge, Western 153 Queen Maud Land

34. Analytical data for the Trollkjellrygg 156 Group, Western Queen Maud Land

35. Radiometric dates for Western Queen Maud 159 Land

36. Summary list of age determinations 161

37. Correlation chart of basement rock units 162 dated from the central Transantarctic Mountains

x i i i FIGURES

Number Page

1. Map of Antarctica 3

2. Histogram of radiometric dates from 3 the Transantarctic Mountains

3. An example isochron diagram 12

4. Multiple isochrons: a method for 24 resolving scatter

5. Plot of Eimer and Amend standard analyses 20

6. Error of isotope dilution analyses for 30 Sr v s . Sr concentration

7. Error of isotope dilution analyses for Rb 31 v s . Rb concentration 87 86 8. Error of Rb /Sr ratios vs. concentration 32 of Rb and Sr.

9. XRF method: Resolution and intensity with a 35 0.005 inch collimator

10. XRF method: Resolution and intensity 36 with a 0.010 inch collimator

11. XRF method: Resolution and intensity 37 with a 0.020 inch collimator

x iv Counting times required for 1 percent precision compared with window widths

XRF spectrum of G-2, USGS standard granite

Graphical solution by Mack and Spielberg to determine Z^ and Z 2

Graphical solutions to determine the counts necessary to attain desired percent error

Calibration curve forXFACT, the conversion factor between (Rb/SrJ^^p and (Rb/Sr)ID

Isochron diagram for the Littlewood Volcanics, Coats Land, using XRF data

Isochron diagram for the felsic flows of the Patuxent Formation, Neptune Range, using XRF data

Calibration curve to determine Sr concentra­ tion by XRF

Calibration curve to determine Rb concentra­ tion by XRF

Geologic map of the Pensacola Mountains

Stratigraphic column of the Neptune Range

Geologic map of the Neptune Range

Structure cross section of the Neptune Range Number Page

25. Isochron diagram for the Gambacorta 78 Formation, Neptune Range

26. Isochron diagram for the Serpan Gneiss, 84 Neptune Range

27. Isochron diagram for the Serpan Granite, 86 Neptune Range

28. Isochron diagram for the Serpan Granite 87 and Gneiss, Neptune Range

29. Isochron diagram for felsic flows and plugs 90 of the Patuxent Formation, Neptune Range

30. Isochron diagram for the Patuxent 95 Formation, Patuxent Range

31. Isochron diagram for diabase and basalt 98 of the Patuxent Formation, Neptune Range

32. Pooled isochron for the Serpan Granite 1 0 2 and Gneiss and the Gambacorta Formation, Neptune Range

33. Geologic map of the Thiel Mountains 105

34. Isochron diagram for the cordierite- 112 hypersthene quartz-monzonite porphyry, Thiel Mountains

35. Isochron diagram for granitic rocks from 114 the Thiel Mountains

36. Map of the eastern Queen Maud Mountains 118

x v i Number Page

37. Geologic map of the Nilsen Plateau 120

38. Isochron diagram for the metasedimentary 128 rocks, Nilsen Plateau

39. Isochron diagram for the metavolcanic 131 rocks, Nilsen Plateau

40. Isochron diagram for the lonely Ridge 134 Granodiorite, Nilsen Plateau

41. Geologic map of Lonely Ridge, Nilsen 135 Plateau

42. Isochron diagram for the South Quartz 139 Monzonite, Nilsen Plateau

43. Map of Coats Land showing outcrop areas 143 of the Littlewood Volcanics

44. Isochron diagram for the Littlewood 147 Volcanics, Coats Land

45. Geologic map of Western Queen Maud Land 150

46. Isochron diagram for volcanics of the 157 Trolljellrygg Group, Western Queen Maud Land

x v i i CHAPTER I

INTRODUCTION

The Transantarctic Mountains extend across the Antarctic con­ tinent, a distance of about 5000 km, in a broad S-curve from Oates Coast in Northern Victoria Land to Coats Land on the edge of the Weddell Sea. Figure 1 is a map of Antarctica which shows the major geographic divisions of the Transantarctic Mountains. The geology of the Transantarctic Mountains is fairly uniform: a basement complex consisting of metamorphosed sedimentary and volcanic rocks that are intruded by granitic plutons is overlain non- conformably by a series of sedimentary rocks of mid-Paleozoic to

Mesozoic age. The sequence of nearly horizontal detrital sedimentary rocks that overlie the basement complex is known as the Beacon Group and includes tillites of Permian age, succeeded by black shale, coal, and sandstone. This sedimentary sequence was intruded during the Jurassic Period by sills and dikes of the Ferrar Dolerite. Late Tertiary to Recent volcanic activity has occurred in scattered localities from the Queen Maud Mountains to Northern Victoria Land. Many age determinations for rocks from the Transantarctic

Mountains have been published. The majority were made by the K-Ar method and involved separated minerals. The resulting dates are

1 generally only products of the last thermal event that recrystallized the rocks and do not indicate dates of original intrusion or sediment deposition. Faure and others (1968) have compiled the published radio- metric dates from the Transantarctic Mountains into a histogram, Figure 2. Inspection of this plot shows two large peaks centered at the time periods of 150 and 460 m.y. ago. The 150 m.y. peak indicates the intrusion and crystallization of the diabase sills and dikes of the Ferrar Dolerite. The broad peak for the time interval of 400 to 525 m.y. represents the thermal metamorphism of the Ross Orogeny. This orogeny occurred in Cambro-Ordovician time and was ex­ tensive throughout the Transantarctic Mountains. Many rock units were recrystallized by the Ross Orogeny, and thus they no longer pro­ vide "true" radiometric ages, but only "apparent" ages. Nevertheless, several dates have been reported for the period prior to the Ross Orogeny, suggesting that late Precambrian rocks do exist in the base­ ment complex of the Transantarctic Mountains. The recent application of K-Ar analyses of hornblende and the Rb-Sr whole-rock isochron method has resulted in more frequent deter­ minations of pre-Ross Orogeny events because these methods are relatively insensitive to metamorphic resetting. A correlation chart by Grindley and McDougall (1969) of Precambrian and Lower Paleozoic rock units and orogenies incorporates seme of the more recent dates from the Transantarctic Mountains (Table 1). Off Ert MM> LWft

*/ Id

ir«Tnff niu<(

F ig u r e 1, Map o f Antarctica.

AGE DISTRIBUTION IN THE TRANSANTARCTIC MOUNTAINS

o z l l I 3 15 cc

100 200 300 500 600 700 800 MILLION'S OF YEARS Figure 2. (from Faure and others, 1968). GEOLOGICAL ACC 3 KACKLET0 H RANGE PENSACOLA KtNS K0R L 1CX MTV3 QUEEN KAUD KTKS NIMROD GLACIER ACE

r a i o a M .Y ra St«ph»mon 1966 Schmidt ^5, Qlj. Toni l^t'K in k y 1*6?, McGr*e*r ond Vodo 196f, Grindloy and Laird N .T r e 1 9 6 4 . 1 9 6 3 Mkirtouch 1969 Minshsw 1967 1 9 6 9

Dover Sandstone BEACON CROUP BEACON CROUP cuuM zraiovs H slstr Sandstone Diaoonform ity B utton Formation Alexandra Formation Elbow Form ation

d e v o n i a n E llio tt Sand»ton* 4 0 0 Orovn Rides ^ K orlltk Formation FT t o o SILURIAN Unconformity Unconformity • Unconformity Uncenfoim lty

• •» ORDOVICIAN g r a n i t e H i n s o t a t ^GRANITE KAJtBOUl g r a n i t e wasotR • . GRANITE JtUISOVR

5 0 0 3H IR U 3 IY E3 * INTRUSIVE* « srmustves *** XNTRUSIYES 5 0 0

0035 OAOOEmr I ROSS OROGENY . ROSS OflOCW ^ ROSS OROGENY « ROSS OROGENY Vi«n« Formation • * BYRD CROUP Gambacorta Volcanic* fU iyollta flow* Taylor Formation Starshot Formation T * T CAMBRIAN Vhieluviy Liaiatcn* Nolsen LlnoSton* U n ratt Formation Hanton Karblo Shaeklaton Limestone A A A rolrw aothar Formation Quartxltoa A 6 0 0 6 0 0 • U n c a n f d i m l t y ? Unconformity *• Unconformity? Unconformity? • Unconformity *• Grar.odlorita • Hyatt KtUvolcanic* Vyatt M otavoleanias ,

HEARDHQRE ORXEXT . BEARDHGRE OflOCDfT • BEAflBHOAt OROCMY SEARCHORE OAOGENT DEAR M O R E OR X ENT 7 0 0 7 0 0 * BEAJIDHORI CROUP

UTTEH Tump lk» Patuxent U Ooro* and La Corea and C o i d i o a n d

0 0 0 HataaorpHlea fflrutign t Thiol Formations Duncan Forsationa Cebham FormatIona 0 4 0

*Jthyollta A porphyry ^OroAodlorito

PHQTt3*OtOIC Llttlivood V oieulei

9 0 0 9 0 0

i p o o ip o o

y j > 0)OD a i o c m ? NIMROD CROCtKT? VDffOD OROCEKT? * j c c a o D o r o g e n t

MIDDLE . SmCJCLETCW a NIMROD CROUP KETAMOflPKICS Cnaies* schist, iophlbollti, id ilit, Gnotai, ochiat, ■erbl*, quartxit*, p a r * c n * l s * marble, qu*rt«lte# aaphibolit# TJOO pnoTEAozote UM m phlbol 11» Table 1. Correlation of Precambrian and Lower Paleozoic Rocks in the Central Transantarctic Mountains (from Crindley and McDougall, 19&9). ^Radiometric Date A—Archaeocyatha T—Trllobites FF—Marine Fauna Inspection of this chart shows that in several areas the base­ ment complex can be divided into three units, each terminated by an orogeny. The oldest rocks of the basement complex are high-grade metasediments and orthogneisses of the Nimrod Group (Grindley and others, 1964). The next younger rocks are metamorphosed sedimen­ tary rocks of late Precambrian age, termed the Beardmore Group (Gunn and Walcott, 1964). Overlying the Beardmore Group is a series of carbonate rocks, clastic sediments, and volcanics of Cambrian age, known as the Ross System (Grindley and Warren, 1964). The youngest rocks of the basement complex are granitic rocks referred to by Gunn and Warren (1962) as the Granite Harbour Intrusives. Radiometric dates on the basement rocks of the Transantarctic Mountains tend to cluster around periods of intrusion and metamorphic recrystallization. Grindley and McDougall in Table 1 indicated the pervasive nature of the Ross Orogeny and also found evidence for two earlier orogenies: (1) the Beardmore Orogeny, 620-680 m.y. ago, and (2) the Nimrod Orogeny, in the period 1050-1000 m.y. The objective of this study is to investigate the geologic his­ tory of the Transantarctic Mountains prior to the Ross Orogeny. The method of study utilizes the determination of ages of basement rocks by the whole-rock Rb-Sr isochron method. The events to be deter­ mined are the time of deposition of sedimentary rocks, the original intrusion of igneous rocks, and the periods of subsequent meta- morphism. This is the first systematic attempt to reach these objectives. All previous attempts have relied on radiometric dates published in the literature. These published dates were not obtained by the whole-rock Rb-Sr isochron method and were susceptible to resetting during metamorphism. For this purpose, samples were analyzed from four areas in the Transantarctic Mountains and from Western Queen Maud Land. These areas are indicated in Figure 1, and are, in order from the Ross Sea to the Weddell Sea: the Nilsen Plateau, the Thiel Mountains, the Pensa­ cola Mountains, Coats Land, and Western Queen Maud Land. CHAPTER II

THE RUBIDIUM-STRONTIUM WHOLE-ROCK ISOCHRON METHOD OF DATING

Law of Radioactive Decay

Rubidium-strontium geochronometry is based on the spontan- 87 eous decay of the naturally occurring isotope of rubidium, Rb , to 87 Sr by beta particle emission with the decay probability of 1.39 x lO”11 per year throughout geologic time (Aldrich and others, 1956). The 87 product of this decay, Sr ', is stable and thus its abundance increases 87 with time. The present-day abundance of Sr in a rock is the total of any initial Sr 87 present when the rock became a closed system and the

0 7 O 7 Sr produced by decay of Rb within the rock since that time. If the 87 amount of this radiogenic Sr can be determined, and if the Rb content is known, then the age of the rock can be calculated, provided it has not gained or lost Rb and Sr. The equation of the law of radioactive decay states that the number of atoms , N, decaying per unit time, t, is proportional to the number of radioactive atoms present:

^ (!) d t

7 where X is the decay constant, 1.39 x 10 ^ per year and N is the 87 number of atoms of Rb present at the time of analysis. Consider the time when the rock system became closed t and the length of time from t to the present as t. Then the integration of equation (1) from t to t yields

N ^ No (2)

where N o is the number of radioactive atoms present at t . o Although it is not possible to determine NQ, N and the number of atoms produced by the decay (daughter atoms), *D, can be deter­ mined. Equation (2) is rewritten using the relationship,

*3) - A/o -N and then becomes

* 3 (3)

87 The daughter atom in the Rb-Sr method is Sr , whose abundance 87 at the time of analysis. Dm, is the sum of radiogenic Sr produced 87 within the system during time t, *D, plus any Sr initially present at 9 Including this relationship in (3) yields

3 u a-Z>a + /v («**-/) (4) which in the Rb-Sr method can be rewritten

j C , = X 7+

Precision of measurement is achieved by determining the abundance of 86 each of the above atoms relative to a stable Sr atom, Sr . The final form of (5) is then written as

(:* ” 1 “ ( i ' H ? * 1 ,1

Isochron Diagram

Notice that equation (6) at any time, t f is of the form

y = . b -+• X/rK > which describes a straight line of slope m and intercept on the y-axis 87 Rfi of b. Plotting data which fit (6) on coordinates of Sr /Sr and 87 PR Rb /Sr produces an isochron diagram. Nicolaysen (1961) originally described such a plot. The slope of a line, the isochron, thus formed is (e t-l), and its intercept on the Sr^/Sr^ axis is Sr^/Sr^ . 10 In order for a suite of rock samples to plot in a colinear array, forming an isochron, certain geologic conditions must be met. (1) They must all have the same age. (2) They must have had the same initial 87 86 Sr /Sr ratio. (3) They must have remained closed systems to Rb and Sr since the last isotopic homogenization. The "age" calculated from an isochron may have several mean­ ings. Ideally, the age of an igneous or metamorphic rock will corres­ pond to the time elapsed since intrusion or metamorphism. If prolonged cooling has taken place, the calculated age will be the time when Rb and Sr are no longer mobile. If the rock has undergone several periods of metamorphism, the age will be the time of the last metamorphic event which mobilized Rb and Sr. Isochron diagrams conveniently display much information: 87 86 87 (1) the values and range of the several measured Sr /Sr and Rb / 86 87 86 Sr ratios (2) the initial value for Sr /Sr (3) the relative age of the rock—higher slopes mean older ages and (4) the "degree of fit" to a true straight line. Note that the degree of fit is actually a test of the required geologic conditions discussed in the previous two paragraphs.

Isochron Analysis

Two computer programs were available to determine the best fit of isochron lines. One of these is a linear regression of x on y and y on x written for the IBM 1620 computer by Mason Christner, a former student in the Ohio State University Geology Department. This program produced very acceptable results, but did not allow weighting of data 11 points in determining a best fit. The second method was the "Least Squares Cubic Equation" developed by York (1966). York's computer program was adapted in Fortran IV for use on the IBM System 360 Model

* 75 computer at the Ohio State University Computer Center. This method allowed the x and y values for each data point to be weighted by a factor equal to the reciprocal of the square of the standard deviation. Figure 3 is an example of an isochron diagram. If the array of data points is analyzed for a best fitted straight line by York's method, the following procedure is used. The input data deck to the computer program consists of eight cards. The first card is a title card, des­ cribing the isochron. The second card contains an estimate of the slope of the isochron and the number of points to be fitted. The fol- 87 86 87 86 lowing six cards contain the Rb /Sr and Sr /Sr values and their respective standard deviations for each data point (shown as bars through the points in Figure 3). York's program, which is listed in Appendix I, provides the 8 7 86 following output. The slope and Sr /Sr intercept of the best fit straight line, labeled A in Figure 3, are calculated, together with their standard deviations. The "center of gravity" of the weighted data points is termed the Centroid of Revolution (shown by an asterisk). Its coordinates are XBAR and YBAR. Through this point the maximum and minimum slopes of the best fit line may be constructed utilizing the standard deviation of the slope of line A. These limiting slopes 87 86 provide the estimate of the standard deviation of the Sr /Sr inter­ cept . Lines B and C have been drawn parallel to line A and through the 12

Sr

Figure 3. An example Isochron diagram. 13 maximum and minimum intercepts. The band bounded by these two lines, together with the analytical error bars for each data point provide a visual check on the compatibility of any one point to the best fit

isochron. In some cases the scatter of points about an isochron is much greater than would be expected on the basis of analytical error. Such a situation is shown in Figure 4. This non-linearity is produced when the rocks analyzed do not conform to the necessary conditions for the formation of an isochron: (1) have the same age, (2) the same initial R7 ftfi Sr /Sr ratio, and (3) remained closed systems to Rb and Sr since isotopic homogenization. The usual method of analysis would involve fitting one isochron to all of the data. When this is done in this case, Line A is the cal­ culated best fit isochron. However, the scatter is such that a large uncertainity exists for the slope and intercept of isochron A. The following method is suggested as a means of reducing the uncertainity in the calculated age. The rocks are assumed to be all the same age and to have remained closed systems to Rb and Sr since isotopic homogenization. The observed scatter is then ascribed to real differences in initial R7 fifi Sr /Sr ratios. Such differences may have arisen by varying degrees of contamination by or assimilation of Rb and Sr from crustal rocks. 8 7 86 In order to minimize the effect of the range of initial Sr /Sr ratios present, several nearly parallel but not colinear isochrons are fitted through subsets of the total data points. Such "subisochrons"

(labeled B and C in Figure 4) are closely parallel to isochron A. 14

Sr

Figure If.. Multiple isochrons: a method for reaolving scatter. 15 Isochrons B and C are by construction very good representatives of the age of the rock samples which define them. The error in the calculated slope and Intercept for each subisochron is much reduced in comparison with the similar values associated with isochron A. An estimate of the age of all the rock samples may be obtained by a weighted average of the subisochron dates. These dates are weighted according to the number of points defining the subisochron. The error of the estimated age is calculated by a standard combined error formula. The initial Sr 87 /Sr 86 ratio reported is not a single value/ but instead is the range of ratios for the subisochrons. The resulting weighted age has a lower associated error than the total isochron result (A), reflecting the assumption that the rocks are indeed all the 87 86 same age. The reported range of initial Sr /Sr ratios reflects the observed scatter in the data, but does not add an unreasonably large error to the isochron age.

Sample Preparation for Rubidium and Strontium Analysis

The size of available samples ranged from hand sample size to fifty grams. Samples were sawed in half or broken with hammer and chisel, half being used for thin-section preparation and the other half for Rb and Sr analysis. Where sample size permitted, outer, weathered layers were discarded. The rock was pulverized in a steel mortar until all particles passed through a 1 mm screen. Any particles finer than 200 mesh (74 microns) were removed by sieving at this stage. The 16 coarse fraction was then completely pulverized to -200 mesh size in a

Spex Mixer Mill. The previously separated -200 fraction was then added to this fraction and mixed for five minutes in the Spex mill (its capacity is about 50 grams) to insure homogeneity of the powder.

Pressing of pellets for XRF analysis Three grams of the mixed powder were weighed out for pressing into a pellet for x-ray fluorescence analysis. The pellet was prepared as described in Norrish and Chapell (1967). Very quartz-rich samples required the addition of 5-6 drops of demineralized water to improve the coherence of the powder after pressure was released. Seven grams of crystalline boric acid were used to form the back and sides of the 1-1/2 inch diameter pellets, which averaged 3/8 inch in thickness. The cylinders confining the powder were stainless steel; the face that formed the outer side of the pellet was kept flat and polished with diamond-dust pads. A Spex hydraulic press was used, pressure being kept at 12 tons per square inch for 1-2 minutes and then gently re­ leased. Very quartz-rich samples maintained coherence best under lower pressure, 8-10 tons per square inch.

Dissolution of rock powders For mass spectrometric analysis, 1/2 to 1 gram of rock powder was accurately weighed and dissolved in a covered Teflon dish in an acid solution consisting of 15 ml hydrofluoric acid, 3 ml sulfuric acid, and 2 ml nitric acid. This solution was kept at low heat on a hotplate overnight. The residue was re-dissolved in about 20 ml of IN 17 hydrochloric acid, filtered through S and S 589 Blue Ribbon, or 589 Black Ribbon filter paper and then tagged with 5 to 10 drops of Sr 89 tracer solution, Sr and Rb were separated using Dowex SOW - x8 cation exchange resin. Separations for isotope dilution and for isotope ratio analysis were done on different sets of columns. The cations was eluted with 2.25 N hydrochloric acid; Sr was detected by the tracer activity and Rb by its relative position to strontium and potassium, detected by a flame test. The eluant was collected in 15 ml beakers; the one or two beakers having the most Sr or Rb were chosen for analysis and evaporated to dryness in a 5 ml Vycor beaker. A few drops of perchloric acid were added to decompose any resin present. The beaker was then covered and stored for later analysis. Water was double-distilled and demineralized. The hydrochloric and nitric acids used were reagent grade and distilled in Vycor glass. Teflon dishes and Nalgene and Vycor beakers were thoroughly soaked and rinsed in demineralized water and 2.25 N hydrochloric acid before u se .

Mass Spectrometric Methods

Sr^/Sr^ analysis The isotope composition of Sr was measured on a mass spec­ trometer. The mass spectrometer used was a Nier type, solid-source in­ strument, having a 6-inch radius, 60°-sector analyzing section (Nuclide Corp., Model 6-60-S), equipped with a single-filament source. 18 _7 Strontium analyses were made at pressures varying from 4x10 to “8 1x10 mm of mercury and at 1.1 to 1.3 amperes filament current. _7 Rubidium analyses were made at pressures less than 6x10 mm of mercury and a filament current of about 0.25 amperes. During an isotope ratio measurement, the mass spectrum of 86 88 strontium from Sr to Sr was scanned at least 96 times at a constant scan rate and recorded on a strip chart. Baseline for Sr was88 taken 85 on alternate scans and Rb , if present, was recorded on every scan. In order to minimize nonlinear emission effects, the peaks were summed in sets of six and isotope ratios calculated for each set. Because of the mass difference between isotopes, fractionation occurs during emission from the filament. Therefore, all measured 07 pc Sr /Sr ratios were corrected for fractionation by assuming that the o c pp Sr /Sr ratio of 0.1194 is constant in natural strontium and multiply­ ing by a factor, f:

r _ (7) O .H 9*

Computer processing of Sr 87 /Sr 86 analyses. Beginning in January, 1970, all data analysis for isotope ratio measurements was done with a computer program written by the author. Data input was by means of punched cards, one card per scan. The program summed peak heights in sets of six, calculated ratios, corrected for fractionation and the presence of Rb 87 , if any, and determined the standard deviation 87 86 of the final average ratio Sr /Sr 19 The program also produced two plots, using the line printer: uncorrected Sr^/Sr*^ vs. Sr^/Sr®®, and corrected Sr^/Sr^vs. set number. These plots proved very helpful in analyzing the quality of the run; any systematic trends, scatter, or unusually high or low values 87 86 of the Sr /Sr ratio were easily apparent. The program then re­ processed the data at least twice, discarding ratios which differed from the mean by more than twice the standard deviation and recalculating new averages. A trial program was also run which calculated ratios from sets of two scans instead of six, but this proved to introduce con­ siderable scatter in the results and made the ratios too sensitive to emission variations. All programs used for this study and several print-out examples are included in the Appendix. Analyses of a Sr 87 /Sr 86 standard. As a check of the validity of isotope ratio measurements, and interlaboratory standard, the Elmer and Amend strontium carbonate standard (Lot 492327), has been anal- 87 86 yzed 25 times since June, 1965. The mean of these Sr /Sr ratio analyses is 0.7082 - 0.0005 ( ) . These 25 analyses are plotted in Figure 2 on co-ordinates of (Sr^/Sr^)m and (Sr^/Sr^)m. The linear array formed is due to the systematic fractionation of the strontium isotopes during mass spectrometric analysis. The correction factor of 8 7 86 equation (7) normalizes these measured Sr /Sr ratios to the standard Sr^/Sr®® ratio of 0.1194. Ten analyses of the Eimer and Amend standard have been made during the period of this study, June, 1968 to June, 1970. The data from these analyses are listed in Table 2. The mean value of the 20

0.715

0.713

0.712

Sr Sr 'nrt. 0.711

0.710

0.709

0 . 708 1— 0.1172 0.1176 0.1180 0 . 1181* 0.1188 0.1192 (Sr66/ Sl>8Q,) Figure 5. Plot of iilrner end Aasend Strcntiun Standard analyses. 21

Table 2: Analyses of Elmer and Amend Strontium Carbonate Standard During the Period June, 1968, to June, 1970

Date Sr87/Sr86 Sr86/Sr88 (Sr87/Sr86) c Analyst

29July68 0.7104 0.1183 0.7070 Eastin 20Aug68 0.7086 0.1193 0.7083 Jones 20Mar69 0.7099 0.1188 0.7081 Eastin 30April69 0.7088 0.1192 0.7082 Tremba 290ct69 0.7121 0.1181 0.7082 Misra 310ct69 0.7120 0.1181 0.7083 Carwile 6Feb70 0.7100 0.1184 0.7069 Eastin

H Feb70 0.7130 0.1175 0.7073 M isra 8April70 0.7121 0.1180 0.7079 Carwile 14June70 0.7119 0.1178 0.7072 Gunner 22 o7 oc 4 * corrected Sr /Sr ratio during this period was 0.7077 - 0.0005 ( <^ ).

Isotope dilution analysis Isotope dilution methods were used to determine the concentra­ tion of rubidium and strontium in the early stages of this study. In this method the concentration of an element is measured by the change in an isotope ratio produced when a sample solution is combined with a spike solution, artificially enriched in one isotope, "diluting" the spike solution directly proportional to the concentration of the element in the sam ple. The isotope composition of rubidium and strontium is constant, 87 87 except for the decay of Rb and the resulting increase of Sr . The isotope composition of these two elements is given in Tables 3 and 5. In contrast to these natural compositions are the spike solutions. These solutions were obtained from Oak Ridge National Laboratories, batch

No. LH-1368-A for the Sr®^ spike and batch No. LY-1448-A for the 87 Rb spike. The isotopic compositions of these spikes as given by Oak Ridge and as measured in our laboratory are listed in Tables 4 and 6. Strontium concentration analysis. To determine the concentration 86 of strontium, accurately weighed portions of rock powder and Sr spike were placed into a Teflon dish and the powder was dissolved, as des- 88 88 cribed before. The Sr /Sr ratio of this homogenized mixture was then measured on the mass spectrometer; six to nine sets of six scans were measured for each analysis. The following equation was then QC QO used to convert the measured Sr /Sr ratio to a ratio of total Sr atoms in the sample to total Sr atoms in the spike: 23 Table 3: Isotope Composition of Normal Strontium

Isotope % Abundance Atomic Weight (amu)

Strontium-84 0.56 83.91343 Strontium-86 9.87 85.90929 Strontium-87 7.04 • 86.90889 Strontium-88 82.53 87.90564

Table 4: Isotope Composition of Spike Strontium (as % abundances)

Sr-84 Sr-86 Sr-87 Sr-88 Lab

0.014 97.644 0.654 1.687 O.S.U. 0.015 97.642 0.658 1.658 Q.S.U. .050 97.60 0.680 1.730 Oak Ridge 24

Table 5: Isotope Composition of Normal Rubidium

Isotope % Abundance Atomic Weight (amu)

Rb-85 72.15 84.91180 Rb-87 27.85 86.90918 The atomic weight of this rubidium is 85.46807

Table 6: Isotope Composition of Spike Rubidium (as % abundances)

Rb-85 Rb-87 Lab

0.805 99.195 O.S.U. 0.840 99.160 Oak Ridge 25

N • + £ • a i r ( M l \ - „ — (8) VA.W"r'»t AJ ■ + -<£ •

where N = total strontium atoms in the weighed sample powder S = total strontium atoms in the spike solution 8616 86 Ab,T = percent abundance of Sr in the sample N 88 88 Abw = percent abundance of Sr - in- the sample Abg 86 = percent abundance of Sr in86 the spike Abg 88 = percent abundance of Sr 88in the spike

The equation was solved for the ratio N/S; this atomic ratio is then converted to a weight ratio by multiplying by the factor:

f _ atomic weight of sample strontium atomic weight of spike strontium ' *

This factor is necessary because the atomic weight of Sr in a sample varies with the amount of accumulated radiogenic Sr 87 . Therefore, the isotope composition of Sr in the rock must be known in order to deter­ mine its concentration accurately. The converted weight ratio,

(e?) . , is then solved for N, the weight of strontium in the rock, by D Wt • substituting the known value, S, previously determined by a spike calibration analysis. Rubidium concentration analysis. The determination of Rb con­ centrations by the isotope dilution method was similar to the method just described for Sr. The following equation was used to convert the 26 87 85 Rb /Rb ratio measured with the mass spectrometer to the ratio of Rb atoms in sample and spike, N/S:

- /V* * JL « d lr J L I At-at-Z+i.aif

In this case, an isotope ratio analysis of the Rb in the rock was not necessary, because the isotope composition of Rb in natural systems is the same at any one time. Spike calibration. The concentration of the spike solutions was measured by isotope dilution, using a "shelf solution" of normal iso­ topic composition. The strontium was made from spec-pure strontium nitrate from Johnson, Mathey, and Co., Ltd. The calibrations of the spike solutions are listed in Tables 7 and 8. Contamination estimates. As a measure of the contamination introduced by a sample processing, "blank" analyses have been made on Rb and Sr. These analyses used all the usual glassware, ion- exchange columns, spike solutions, etc., but no sample was added to dilute the spike. The resulting calculation for the weight of "sample" Sr or Rb is a measure of contamination that has occurred. Blank run data are presented in Table 9. Calculating reproducibility for ID and IR analyses. In an at­ tempt to estimate the error for isotope dilution measurements and the associated Rb 87 /Sr 86 values, a compilation was made for all duplicate isotope dilution and many duplicate isotope ratio analyses made in our 27 Table 7: Calibrations of Sr-86 Spike Solutions

Date Sr Concentration

28Mar68 5.085 /tg/g 28Mar68 5.062 31Aug68 5.051 average: 5.066 29Aug68 5.203

29Aug68 5.163 30Aug68 5.192 average: 5.186 1 Jul69 5.096

3Jul69 » 5.130 average: 5.113

Table 8: Calibrations of Rb-87 Spike Solutions

Date Rb Concentration

30Aug68 5.167 /*g/g 31Aug68 5.251

1Nov 68 5.134 average: 5.184 8Jul69 5.045 9Jul69 5.127 average: 5.086 28

Table 9: Rb and Sr Blank Analyses (from Fenton, 1969)

D ate Sr (jug/g) Rb (^ug/g)

Sept6 7 0.167 0.148

Dec67 - 0.061 Apr68 0.108 0.019 Aug68 0.108

average: 0.128 0.076 29 laboratory. The average difference between Sr ID duplicates, expressed as a percent of their mean, is - 0.82%; for Rb this value is - 2.92%. X + The average difference on Sr IR duplicates is - 0.13%, or - 0.0009 in • -87 86 units of the Sr /Sr ratio. The average difference of duplicate deter-

87 86 4* minations of the Rb /Sr ratio is - 3.23% for samples having less than 50 ppm of either Rb or Sr and - 0.96% for samples having more than 50 ppm of both elements. Because samples having low concentrations of either Rb or Sr (less than 10 ppm) are difficult to determine with precision, such measurements usually have a higher per cent difference between dup­ licates than do samples having higher concentrations. To attempt to illustrate this relationship, three plots were made, shown in Figures 6, 7, and 8. In each plot the measured value is plotted against the per­ cent difference between duplicate determinations. The expected rela­ tionship is only apparent for SrID measurements. Part of the reason for the scatter shown in these plots is that only those measurements which are suspected to be in error are likely to be made in duplicate. In addition, the large errors expected for low concentrations may be coun­ teracted by the analyst using great care on these measurements, which he knows will be difficult.

X-Ray Fluorescence Methods

Measurement of the Rb/Sr ratio by x-rav fluoresence Because about 100 samples were analyzed in this study, the lengthy procedure of isotope dilution would have been impractical. Sr concentration (ppm) 1000 100 iue , ro f stp dlto nlss f strontium of analyses dilution isotope of Error 6, Figure 10 0 © a© vs. strontium concentration. strontium vs. 1 ifrne ewe ulcts (as duplicates between Difference 2 3 h v. %) 5

50 6 31

1000

10 0 1 2 3 h 5 6 Difference between duplicates (as$) Figure 7. Error of isotope dilution analyses of rubidium vs. rubidium concentration. 32

10

on

0,1 0 1 3 b 6 Difference between duplicates (as %) Figure 8, Error of Rb87/Sr36 ratios vs. concentration. 33 Instead the Rb/Sr ratio for most of the samples was determined by x-ray fluorescence. There were two reasons for measuring the ratio, Rb/Sr, instead of individual concentrations; (1) Isochron analyses require only the Rb/Sr value and the Sr-isotope composition. (2) Measurement of the Rb/Sr ratio by x-ray fluorescence is inherently more precise than the measurement of concentration. In addition, use of the XRF method, with the capability for many repeated analyses of each sample, also produced a better estimate of the reproducibility of the Rb/Sr ratio. This increases the reliability of weighing factors used for fitting iso- chrons by York's method. Principles. The method of x-ray analysis which was adopted was similar to that used at Massachusetts Institute of Technology (Faure, personal communication) and at our laboratory by Solter (1966). The underlying principle is quite straightforward: the concentration of a trace element in a sample is directly proportional to the product of the mass absorption coefficient of the sample, y u , and the net inten­ sity of the K-alpha radiation of the element 1^^. . For Rb and Sr the relationships are:

(ID

(12) 34 where K is the proportionality constant. Reynolds (1963) noted that K is a function of (1) the efficiency and design of the particular x-ray spectrometer being used, and (2) the basic relations that govern the generation of K-alpha radiation being used. If the ratio of two elements is determined, the mass absorption coefficient drops out of the resulting equation:

(13) where XFACT is the new proportionality constant. A very similar ap­ proach was described recently by Doering (1968). Instrument operating conditions. The x-ray emission spectro­ meter used was a General Electric XRD 6 with SPG 4 spectrometer and detector. A molybdenum target tube was used because of its high ef­ ficiency in exciting fluorescent radiation from Rb and Sr. The tube was operated at 70 kilovolts and 50 milliamperes; it was found that increas­ ing the tube voltage to near its rated maximum produced the greatest intensity of Rb and Sr K°c radiation. Three exit collimators were available, having 0.02, 0.01, and

0.005 inch blade spacings. The 0.01 collimator was found to produce a good compromise between high intensity, and resolution. Figures 9, 10, and 11 are representative scans of the Rb and Sr K-alpha peaks

analyzed with the three collimators for comparison. A lithium fluoride (200) crystal, d = 4.0267, was used initially. It produced high peak intensity, but, because of its low resolving power, it barely resolved Counts par second (cps) liOO 300 iue . E Mto: eol i n i enst t a 0.005 a ith w sity n te in and n tio lu reso Method: KEF 9. Figure M-69-56: AGV-1: — GSF-lt r 27 ppm 237 * Sr r 67 ppm 667 = Sr b 26 ppm 256 = Rb ^ 5 3 3 3 39 38 37 36 . 35 3^ nh oli or. to a llim co inch O- 0-0

ere 2-heta -th 2 Degrees Sr Rb

1100

1000

900

800

700

o 600

^00

400

o-o 300

Sr Rb 200

35 36 37 39 Dogreoa 2 - theta Figure 10. XRF Method; resolution nnd intensity with a 0.010 inch collimator. lljOO

AGV-1: Rb = 62 ppn 1300 £r - 667 pftn — K-69-56: Rb = IjOO ppra Sr - 2*3 ppm 1200

1100

1000 -

9 0 0-

900-

70 c-

Sr Rb 60C

500 Degrees 2-theta Figure 11. XRF Method: rosolutlon and Intensity with a 0,020 inch collinator. the Rb and Sr K-alpha peaks for samples with high concentrations of either element. In addition, the baseline under the Rb and Sr K-alpha peaks was appreciably curved because the presence of the nearby MoK-alpha line of the x-ray target. Following a suggestion by J. L. Powell at Oberlin College, a lithium fluoride (220), d = 2.8480, crystal was purchased. The small d- spacing of the (220) planes in this crystal produced larger 2-theta angles in the diffracted radiation, which greatly improved resolution and background linearity. Slightly lower intensities were a worthwhile sacrifice. The crystal was aligned and periodically checked with the zirconium K-alpha line at 32.10° 2-theta. An additional improvement was the enlargement of the window between the sample box and the x-ray tube. This allowed the full surface area of the sample pellet to receive x-rays and increased intensities by about 50%. The radiation was detected with a scintillation counter using a sodium iodide, thallium-activated crystal. Its usual operating voltage was between 695 and 725 volts. The optimum voltage was determined at 30 KV, 20 ma tube current with the Zr K-alpha line generated by a piece of zirconium foil in the sample holder. This procedure was followed each day of operation. Amplifier gain was set at maximum ( coarse = 16, fine = 87) so as to minimize counter voltage and the resulting "noise." Pulse height analysis was used with a baseline of 2 volts and a window width of 5 volts. This window was found to produce the shortest counting times, a compromise between the peak- to-background ratio and peak intensity. Figure 12 is a plot of window iue 2 Cutn tm3 eurd o oe ecn accuracy- percent one for required time3 Counting 12, Figure n r n R Kapa ek o BR1 s window widths. BCR-1 vs, of peaks Rb K-alpha and Sr on

Seconds Seconds 0 0 5 2 2100 1900 2200 2000 160C- 100 3^567 j. i dw it (volts) Window width -O <3 x

Sr 36 ppm 336 r: S r o F R: | ppm 1|4 Rb: r o F 39 10 10 39 - 40 width vs. time required to determine both strong and weak K-alpha in­ tensities with 1% accuracy. Counting procedure. Fixed-time counting was used, manually resetting the goniometer after each count. In this way "scans" were made, each ten to twenty minutes in duration, over the 2-theta range encompassed by the K-alpha lines of Rb and Sr and their adjacent back­ grounds. Five positions were used: Background (1) at 35.00°, Sr K-alpha at 35.85°', Background (2) at 36.92°, Rb K-alpha at 37.99° , and Background (3) at 41.50° . Background positions were chosen so as to be free of any interfering peaks,not necessarily symmetrically about the K-alpha lines. A sample spectrum is shown in Figure 13. The counting times at different positions during one scan varied from 20 to 400 seconds. The available times were limited by the scaler design to 20, 40, 100, 200, 300, and 400 seconds. The method of dividing available time between the five counting positions was based on the method of Mack and Spielberg (1958). They summarized their paper as " . . . how best to divide the available time to obtain the greatest precision in the measurements. " All samples were scanned with fixed-time 10-second counts to determine intensities at each position and to calculate peak-to-back- ground ratios (total intensity -f- background) for the two K-alpha positions. The plots of Mack and Spielberg shown in Figures 14 and 15 were then used to calculate the required counts on the Rb and Sr peaks to produce an accuracy of 1% at the 90% confidence level. Samples were scanned using times calculated by this method or H -p» M ct 03 03 O O CD ^ £ Sr K-alpha * Ho Ho K-beta Compton Ho K-beta Ko Ko K-alpha Mo K-alphaMo Compton Sr K -betat Zr K-alpha — Intensity — Background 0 Rb Rb K-alpha

Rb Rb K-beta, Y K-alpha Background 2 Th Th L-alpha 1, Pt LY-1 ^Background Ct J Fb L-beta 1 " 00 . 30 39.23- 1*1.50- \ Background1*0.35" 3 Figure 13 42

z t

Figure llj.. Graphical solution by Mack and Spielberg (1958) to determine and Z2 for use in Figure 15.

Figure 15. Graphical solution by Mack and Spiel­ berg (1958) to determine the x-ray count necessary to attain the desired percent error. Error levels are given at the top of the chart. Confidence levels of 5 0 3 90, and 99 percent are indicated by the solid, dotted, and dashed lines, respectively. 43 fractional times, if the rate was too low to achieve the total time in one scan, until a standard deviation of 1% or better was achieved for the Rb/Sr intensity ratio. The number of scans per sample varied from three to eight; most samples received five scans.

Calibration curve. In order to determine XFACT, about forty samples were chosen from the laboratory collections which had been analyzed in duplicate by isotope dilution. Three grams of powder from each sample were ground to -200 mesh, pressed into pellets, and analyzed many times by XRF to determine the Rb/Sr net K-alpha intensity ratio. In addition, the U.S.G.S. rock standards, AGV-1, BCR-1, G-2, GSP-1, and W-l were similarly analyzed. These data were then plotted as (Rb/Sr) _ vs. (Rb/Sr)VDP and a best fit straight line was calculated ppm a Kt using York's regression method. This plot is shown in Figure 16. XFACT was thus calculated as the slope of this straight line, 1.2840, with an error calculated as - 0.0195 ( - 1.52%). Isochrons by both XRF and isotope dilution. To further test the validity of the x-ray results, two groups of samples, previously anal­ yzed by isotope dilution, were analyzed by x-ray fluorescence. The calculated ratios of the concentrations of Rb and Sr determined by both methods are compared in Table 10. Two samples showed a very large difference in the Rb/Sr ratios resulting from the two methods. Both of these samples had very low Rb concentrations; 35 7 had 1.8 ppm and 414 had 8.1 ppm by isotope dilution. These low concentrations are difficult to measure by XRF, as many scans are required. These samples received only three scans, a minimum. Contrary to this reasoning, 12 1.0

470 0.8 76B o 10 0.6

313. ©S3

Q 128-6 n

XFACT = 1.281*0 353 e ±0.0195 C<0

(Rb/Sr) XRF Figure 16. Calibration curve to determine XFACT, the conversion factor between (Rb/Sr)IO .p* and (Rb/Sr)XRF. »

45

Table 10: Comparison of Rb/Sr Ratios Determined by X-Ray Fluorescence and by Isotope Dilution

Sample (Rb/Sr)ID %Difference (Rb/Sr)XRF a

367 1.2833 1.3170 - 2.6 405 0.9496 1.0271 -7 .5

406 0.8314 0.8295 + 2 .3 407 5.0164 5.3279 -5 .8 408 0.1240 0.1309 -5 .2

409 8.5581 8.4211 + 1 . 6

352 0.2557 0.2583 - 1.0

353 2.3731 2.3730 + 0 , 1

354 0.1083 0.1131 -4 .3

355 1.3955 1.4092 - 1.0 356 0.9618 1.0309 -6 .7

357 0.0233 0.0449 -4 8 .

290 1.5488 1.5522 - 2.2 CM iH CM 1 414 0.0635 0.0807 .

41S 0.0048 0.0048 0.0

a100( (XRF-ID)/ID) 46 sample 415 showed 0% difference/ but had only 10.0 ppm Rb. The aver­ age per cent difference in the Rb/Sr ratios determined by the two methods is 3.2%, omitting samples 357, 414, and 415. Isochrons were plotted from both sets of data. The Iittlewood Volcanics isochrons are shown in Figures 17 and 44 . Isochrons for felsic flows from the Neptune Range are shown in Figures IS and 29 . For ease in comparison, the dates indicated by these isochrons are summarized in Table ll. The two methods are shown to produce iden­ tical ages, within the limits of error. The error of the XRF isochrons tends to be higher than the comparable isotope dilution results, but this is probably due to the fact these samples were scanned only three times by XRF. Additional scans should reduce this error. Computer processing of XRF data. Because of asymetric back­ grounds , the tedious calculation of standard deviations, and the tedious 87 86 calculation of errors for the Rb /Sr ratio, a computer program was written and used to analyze all x-ray data. The program was set up to calculate a linear background beneath each peak and to correct for counter dead-time (0.5 x 10 sec). The program averaged the several scans for each sample, calculated a standard deviation and, if a

Sr®^/Sr^ ratio and its error ( 2<£f) was supplied, calculated a RB®^/Sr®^ ratio. The error calculated for this ratio was the combined measurement R7 Rfi errors on XFACT, the (Rk/Sr)xRF rati°/ anc* t^e (Sr /Sr ) ratio. The program is listed in the Appendix. The equations are:

c ^ c = O f - f l l • ** A— (,*) a i r .& L • f i t k f t . % 1.10

1.00

0.90

Sr T = 990*22 n.y. 0.80 (Sr97/sr86)o r 0.7058 *0.0013 ©= Eertrab- Nunatak Littlewood Kunataks -OLOQ 0.70 20

Figure 17. Isochron*diagram for the Littlewood Volcanics, Coats Land, using XRF data.

•p. *0 1179 ±82 ra.y. 502 ±12 m.y

0.760

S r 0.720 435

357 0.700 0 l 2 4 6

Figure 18. Isochron diagram for the felsic flows of the Patuxent Formation, Neptune Range, using XRF data. -t* oo 49

Table 11: Comparison of Isochron Dates Obtained from XRF and Isotope Dilution Methods

Samples XRF Date ID Date

Littlewood 235, 367, plus 0 .705a 1014 - 25 m.y. 1005 - 25 m.y. Bertrab 405, 406, 407, 408, 409 987 - 28 999 - 19 Littlewood and Bertrab 990 - 22 1001 - 16 Neptune R. flows 355, 434, 435 502 - 12 492 ~ 12 Neptune R. flows 352, 353, 354, 357 496 - 17 477 - 18

Neptune R. flows 354, 357, 358, 434 1179 - 82 1210 - 76

aAssumed initial ratio 50 w h ere , CONFAC = factor to convert the concentration 87 86 ratio Rb/Sr to the isotope ratio Rb /Sr 87 0.2785 = abundance of Rb 85.468073 a.u.u. = atomic weight Rb atom ic weight of Sr } caicuiated in program to suit the given abundance of Sr^ ) Sr^/Sr^. ratio

CFflcTF =. 0 ,z S '3 3 3 3 -&*7H£ (16) where, CFACTE = the error in the ppm to atomic Rb/Sr conversion factor S8786E = twice the standard deviation of the 87 86 SR /Sr measurement 0.283333 = the slope of the line in the plot of CONFAC „ 8 7 /„ 86 v s. Sr /S r

HX4/6- -- [/xFfrc7?:\x /s^/w a/V , /c/^-nrV l j (,. 7) .

w h ere , XFACTE = the error associated with XFACT SDMEAN = the error for the Rb/Sr ratio RBSRI = the average (Rb/Sr)XRF ratio 51 then,

(T H X N & f" • ( 18) where RBSRAE the error of the calculated RB®^/Sr^ ratio RBSRAT the RB®^/Sr^ ratio .

Rubidium and strontium concentration by x-rav fluorescence Principles. In order to gain approximate values for concentra­ tions of Rb and Sr in the rock samples, they were all analyzed once by the method of Damon (1966). This method utilizes the same relationship given in the previous section,

(I?)

except that standard pellets are analyzed with the samples to produce a calibration curve, and mass absorption coefficients are measured by analysis of the Compton-scattered molybdenum K-alpha radiation in standards and samples. Hower (1959) showed that a ratio of mass absorption coefficients for two materials remains constant at any wavelength shorter than that of the iron absorption edge. Reynolds (1963) showed that the mass absorption coefficient in the region below the iron absorption edge is linearly related to the reciprocal of the intensity of the Compton- 52 scattered Mo K-alpha radiation (Ij^ q k *C c ^:

I sM* ” *7” (2o) -t-rto K-cc

Damon (1966) combined equations (30) and (31) and showed that the concentration of an element is proportional to the ratio of the K- alpha radiation of the element in question to the Mo K-alpha Compton radiation from the sam ple:

3 / .. pp** * - *pr' (2.1)

Pellets of rock standards analyzed at the same time as the samples are used to construct calibration curves plotted as

Jh. and ---— - /\r\ , pp/m .

This method was attempted early in the course of this study, but difficulties in analysis gave results too imprecise for accurage age determinations. However, a very helpful discussion with Dr. H. W. Fairbaim of the Massachusetts Institute of Technology suggested that background measurements in the 2-theta range of 39-40° are subject to interference by thorium L-alpha and lead L-beta radiation (see Figure 13). It was also suggested that correction for background under the Mo-Compton K-alpha peak produced better results. Accordingly, the third background measurement was changed to 41.5° and an additional 53 background was measured at 28.10° to allow for measurement of the net Compton peak; XRF and isotope dilution results compared. Table 12 provides a comparison between the ppm values of Rb and Sr in the standards with the results from Damon's curves corrected and uncorrected for MoK«c C background. The average percent error for Rb and Sr in the uncorrected background data are 4.6 and 12.5 respectively. Percent errors for Rb and Sr in the corrected background data are 4.5 and 6.0. Figures 19 and 20 are calibration curves for Rb and Sr plotted with background- , corrected MoK< C data. Because of the time-consuming procedure of including standards in each day's analysis, only one such scan was made for each sample. This data is not sufficient to demonstrate the validity of the method or providing reliable values for concentration. Five or more additional scans would undoubtedly provide more convinc­ ing results. Computer processing. The computer program used to process

this data is a modification of a program used by Powell(1969) and is given in the Appendix. Scans were made in the same manner as for the Rb/Sr method. The program fitted straight lines by least squares anal­ ysis to the standard data and determined Rb and Sr concentrations in the samples by multiplication by a factor derived from the slope of the

calibration "curve." 2.0 ppm Sr = (9/j3.68)x(Sr/Mo)j

0.3

1.0 0.2

0.1

15001000 2000 ppm Sr Figure 19. Calibration curvo to determine Sr concentration by XRF. 0.3

0.2

0.1 ppm Rb - (12*56.50 )x(Rb/Ko)

0 100 200 300 500 600 ppm Rb Figure 20. Calibration curve to determine Rb concentration by XRF. 56 Table 12: Comparison Between Rb and Sr Concentrations in Standards as Determined by XRF and Isotope Dilution (concentrations in ppm)

Rb XRF Sr XRF Rb With No Sr With No Sample ID MoBG MoBG ID MoBG MoBG

M -69-69B 144.0 140.2 139.7 236.1 239.0 260.3 L-7 36.4 30.9 31.1 724.8 764.8 840.7 353 264.4 273.7 275.4 111.4 113,2 125.1 76-B 625. 605.3 610.9 58.8 57.0 63.0 290 261.9 267.6 271.8 168.7 169.8 188.6

LV-4 178.6 179.5 180.9 1213. 1510. 1664.

48 112.9 114.6 114.7 198.7 203. 222.2 54 90.6 9 4 .2 94.2 25.9 28.0 30.6 128-6 300. 304. 305. 45.4 4 1 .8 45.8

324 392.8 388.8 391.9 57.5 58.7 65.0 L-47 247.6 227.0 229.4 23.2 19.3 21.4

407 240.5 228.1 227.3 45.1 46.5 50.6 55 7.5 7.0 6.9 19.8 17.8 19.3

338 21.6 23.0 22.8 156.2 159.3 173.9

339 27.1 29.0 28.8 148.9 157.8 172.6 .a Avg. % error: » 4.5% 4.6% 6 . 0% 12.5%

a 100 ( (XRF-ID)/ID) CHAPTER HI

PENSACOLA MOUNTAINS

Physiography

The Pensacola Mountains are part of the Transantarctic Mountain chain and extend for 500 km between 40° and 70° W. longitude, and 82° and 86 ° S. latitude, near the southern edge of the Filchner Ice Shelf as shown in Figure 1. They are subdivided into the Patuxent, Neptune, and Forrestal Ranges and the Dufek Massif, with locations shown in Figure 21. The Pensacola Mountains form a barrier to ice flowing from the polar plateau toward the coast. They reach elevations of more than

1000 m above the surrounding ice, dividing the flow of ice from the polar plateau into three large glaciers: (1) the Patuxent Ice Stream, 154 km wide, between the Patuxent Range and the Thiel Mountains, (2) the Academy Glacier, 60 km wide, between the Patuxent and Neptune Ranges, and (3) the Support Force Glacier, 122 km wide, between the Forrestal Range and Mt. Ferrara. The Patuxent and Neptune Ranges were once covered by glacier ice, as indicated by the presence of striated bedrock on the highest parts of the ranges and by thick mor­ aines in the Patuxent Range (Schmidt and Ford, 1969).

57 58

'• Dgl.li

* 7jfTAughtnbluflh PM l f'h. N»nb«'fl PM* M MdMfo* .C ofdintf

tU o u n l N u n

Schmldl \f.\7 ‘ P*pp»i P*A ^r ' Uti Hillp. N Vi. C m '

►Wf 6M K AUgt

Mt.VjrbrngtiM;v K -(

j i p i j

T oleM n

Figure 21. Geologic /nap of the Pensacola .Mountains (from Schmidt and Ford, 1969). 59 History of Exploration

The Pensacola Mountains were first seen by man during a U.S. Navy transpolar reconnaissance flight in 1956 with W. M. Hawkes as pilot. Augenbaugh (1961) and Walker (1961) described the findings of the first visit to the mountains, after a reconnaissance of the Dufek Massif in December, 1957, as part of the United States' I.G.Y. pro­ gram . Following these early investigations, the U.S. Geological Survey carried out a reconnaissance geological and geophysical map­ ping program in the Pensacola Mountains during the period 1962-1966. Schmidt and Ford (1963) described the geology of the Patuxent Range, and Schmidt and others (1956) that of the Neptune Range. Williams (1969) has written a study of the petrography of the Upper Precambrian and Paleozoic sandstones of the Pensacola Mountains. The layered gabbro intrusion of the Dufek Massif and Forrestal Range has been des­ cribed by Ford and Boyd (1968). Finally, an excellent summary and map of the geology of the Pensacola Mountains by Schmidt and Ford (1969) was published as part of the American Geographical Society's Antarctic Map Folio Series.

Stratigraphy and Structure

Ten sedimentary and volcanic rock formations have been recog­ nized in the Pensacola Mountains. They are divided into three strati- graphic sequences, each bounded above by an angular unconformity. A columnar section from Schmidt and jFord (1969) is shown in Figure 22. COLUMNAR SECTION

11 . Slltetone and ahele iVX'BiXSi. ,» n M M with coelbede t p'*> Mittn FNt ’■rpir-^vj * GalaMudatone (Pio) *000—1 . b'liFffiK Dover Sanditone (Pid)’

-tc.ooo .O/ifonftrmll/ 3 0 0 0 - Heleer San detone n. Elbow Formation a o <5 EllloH Sandal ana

Brown Ridge Conglomerate Wlene Formation 'Unnnfeimllr Si Gambacorta Formation (C*g) Notion Llmoitone (cn) • 'Unconformity

0-L .q Patuient Formation (pCp)

i *Fornu(lan from which hitr* bttn collided

Figure 22. Stratigraphic column of the Neptune Range, Pensacola Mountains. The numbers refer to the geologic cross sec­ tion. Figure 2i|. (From Schmidt and Ford, 1969} 61

The oldest sequence consists of the Patuxent Formation, estimated to be several tens of thousands of feet thick and probably of late Pre- cambrian age. The middle sequence consists of the Nelson Limestone at the base, followed by volcanics of the Gambacorta Formation and the siltstone and sandstone of the Wiens Formation. This sequence, about 1,000 m in total thickness, is of the earliest Paleozoic age. The rocks of the third sequence consist of six formations, totaling 4,000 m in thickness and ranging in age from Ordovician or Devonian to Permian. The oldest unit in this sequence is the Brown Ridge Conglomerate, a massive red poorly sorted coarse conglomerate, ranging from a feather edge up to 1000 m thick. The Elliott Sandstone, the next youngest unit,' is a calcareous sandstone and conglomerate about 700 m thick. The Elbow Formation, a red siltstone and shale unit

300 m thick, overlies the Elliott Sandstone. Above the Elbow Formation is the Heiser Sandstone, a quartz sandstone about 300 m thick. These four formations are grouped by Schmidt and Ford (1969) as the Neptune Group; their upper contact is marked by a disconformity. A quartz sandstone about 1200 m thick, called the Dover Sand­ stone, overlies the Neptune Group. It crops out in the Neptune and Forrestal Ranges, and may be the equivalent of a similar sandstone in the Patuxent Range that contains plant fossils of probable Late Devonian age (Schmidt and others, 1965). Hie Dover Sandstone is separated from the overlying unit, the Gale Mudstone, by a probable dis conformity. The Gale Mudstone is a black pebbly mudstone, probably a tillite and correlating with other 6 2 Late Paleozoic tillites of the Transantartic Mountains (Schmidt and others, 1965). The youngest sedimentary rocks of the Pensacola Mountains crop out on the Pecora Escarpment, south of the Patuxent range, and in the southern Forrestal Range. These rocks are interbedded sandstones and shales, containing black carbonaceous and coal-bearing layers with a glossopterid flora of Permian age (Schopf, 1964). They are similar to Beacon Super-group rocks, but are not known to be in contact with other units in the Pensacola Mountains (Schmidt and Ford, 1969). Part of this study has involved dating the Patuxent and Gambacorta Formations, the basalts, felsic flows, and diabase included in the Patuxent Formation, and the Serpan Granite and Gneiss. In order to interpret the results of the radiometric dates, these units are described in d etail.

Patuxent Formation The type section of the Patuxent Formation is in the Patuxent Range, where it makes up about 90 percent of the exposed bedrock. The formation is also well exposed throughout the Neptune Range, where it makes up about 40 percent of exposed bedrock. The unit may occur as far to the northeast as Mt. Spann in the Argentina Range. The Patuxent Formation consists of grayish-green, rhythmically interbedded subgraywackes and slates. Detrital grains of quartz, rock fragments, and minor amounts of feldspar occur in a groundmass of fine-grained quartz, sericite, and chlorite. In the western part of the Neptune Range, in the Schmidt and William Hills, pillow lavas having an aggregate thickness of 1000 m and basalt flows from 2 to 30 m thick are abundant, interbedded with the sandstones and slates. Sediments of the Patuxent Formation show graded bedding, load casts, current bedding, and channel fillings. Rock fragments in the sandstones con­ sist of chert grains, shale, phyllite, sandstone, siltstone, and basalt (Williams, 1969). The thickness of the Patuxent Formation is estimated to be several tens of thousands of feet. The uncertainty is due to the present occurrence of the formation of tight isoclinal folds and the absence of an exposed lower contact. The Patuxent Formation is unconformably overlain by the Middle Cambrian Nelson limestone and has been thought to be late Precambrian in age by Schmidt (1965).

Nelson limestone The Nelson limestone, the oldest unit of the second sequence, unconformably overlies the Patuxent Formation at an angle of nearly 90° at its type section, 2.4 km south of Nelson Peak on the Washington Escarpment in the Neptune Range (Figure 23). It is conformably over- lain by the Gambacorta Formation. The contact between the two units is exposed on Wiens Peak. The Nelson Limestone crops out in the Patuxent Range, the Neptune Range, and the Schneider Hills, part of the Argentina Range northeast of the Forrestal Range. The formation consists of dark-gray, thin and thick-bedded lime­ stone with a red conglomerate. Total thickness is 180 to 240 m. Three different faunal groups of trilobites and brachiopods of Middle Cambrian age have been identified in the Nelson Limestone; in addition, an Figure 23. Geologic map of the Meptune Hange, Pensacola Mountains (from Schmidt and Ford, 1969). 65 archaeocyathid of probable Early Cambrian age was found (Schmidt and others, 1965).

Gambacorta Formation The Gambacorta Formation is a huge complex of lava and breccia flows, with a few ignimbrites. It is confined to the southern Neptune Range, reaching more than 900 m in thickness at Gambacorta Peak (Figure 23) and thinning outwards until it disappears within 5 to 10 km. The upper and lower contacts are exposed and the formation is in con­ formable succession with the Nelson Limestone below and the Wiens Formation above. The Gambacorta Formation has been divided into six members, as shown in Table 13 (Schmidt and others, 1965).

Wiens Formation The type section of the Wiens formation is on Elliot Ridge in the

southern part of the Neptune Range, to which the formation is limited, and conformably overlies the Gambacorta Formation. In places, the Wiens Formation intertongues with volcanic sedimentry beds of the upper Gambacorta. The formation is unconformably overlain by the Elliot Sandstone of the third sedimentary sequence. The Wiens Formation consists of interlayered green and red- brown thin-bedded shale, siltstone, and fine sandstone, and contains several thin-bedded gray oolitic limestones. The formation is less than 300 m thick, and, together with the Gambacorta Formation, is probably Cambrian in age (Schmidt, 1965). 66 Table 13: Stratigraphy of the Gambacorta Formation, Neptune Range. (Schmidt, wirtten communication).

Member Lithology Sample Numbers

Elliott Rhyolite Rhyolite breccia of the basal Breccia Elliot Sandstone 294 Upper Gambacorta Mostly light green, thin and thick layered, flows and fluvial volcanics

White Porphyry Thick, rhyolitic, probably ash flow units with quartz and two feldspar phenocrysts (Feldspars commonly entirely altered) Hawkes Pyro- Thick dark green ignimbritic 348, 349 cla sties ash flow tuff units with 350, 351 phenocrystic quartz-Kspar- 292, 293 plagioclase clasts. Relatively little altered and consisting of several differentiation phases

Johnson Porphyry Thick, black ash flow unit 391 with distinctive phantom or shadow feldspar phenocrysts

Red-Brown Member Thin red-brown and purple 290 agglomerates, breccias, pyro- 389, 390 clastites and flows; generally low potassium and with quartz and plagioclase phenocrysts Lower Gambacorta Thin, mostly light green, 291 pyroclastic (containing devitrified glass and pumice) tuffaceous and fluvial volcanic units . Commonly contaminated with limestone, probably from the underlying Cambrian Nelson Limestone 67

Igneous rocks

Diabase. Diabase sills 2 to 300 m thick are intruded into the Patuxent Formation in the Schmidt Hills of the western Neptune Range. The sills seem to have been folded at the time of initial deformation of the Patuxent formation and may thus be late Precambrian in age (Schmidt,

1965). Felsic flows and intrusives. Felsic flows 2 to 100 m thick, and plugs about 30 to 55 m in diameter, are interbedded with and in­ truded into the Patuxent Formation in the Schmidt and Williams Hills of the Neptune Range. Together with the basalt flows and diabase sills of the Patuxent Formation, these felsic flows and plugs form a spilite- keratophyre suite penecontemporaneous with the eugeosynclinal depos­ ition of the Patuxent Formation (Schmidt, written, communication). Hypabyssal rhyolitic porphyry. At Nelson Peak, Gambacorta Peak, and Mt. Hawkes in the eastern Neptune Range, hypabyssal rhyolitic porphyry in sills up to 300 m thick, and in irregularly shaped bodies up to 5 miles in diameter, intrudes rock units as young as the Wiens Formation. The porphyry is evidently older than the Brown Ridge conglomerate, because the conglomerate contains porphyry cobbles

(Schmidt, 1965). Serpan granite and gneiss. At Serpan Peak in the eastern Nep­ tune Range a biotite granite gneiss is in intensely sheared contact with the Patuxent Formation. Vertical axial-plane cleavage of the Patuxent Formation may be parallel with the gneiss contact. Foliation in the gneiss also seems to parallel the contact. 68

Just east of Serpan Peak, in an area where gravity study indicates a large deep-seated low-density body, are boulders of coarse-grained blotite granite in moraine deposits. The restricted distribution of the boulders and their similarity in hand-specimen, chemical, and petro- graphic characteristics have led Schmidt (written communication) to suggest that they are derived from a large granite pluton hidden beneath the snow cover east of Serpan Peak. Schmidt and others (1965) have reported two radiometric dates on specimens from the Serpan Granite: (1) a Rb-Sr whole-rock model date of 510 - 30 m .y . and (2) a K-Ar biotite date of 265 - 13 m .y. In addition, a lead-alpha date of 350 - 40 m.y. on zircon from the same granite was reported recently (Schmidt, written communication). Along with this last analysis, Schmidt suggested that each date may have geologic meaning, the spread reflecting the effects of polymetamorphism. Three regional metamorphic events are known from stratigraphic and structural relationships in the Pensacola Mountains:

(1) A pre-Middle Cambrian event which involved folding of the

Patuxent Formation.

(2) A Cambro-Ordovician (about 500 m.y.) event, the Ross Orogeny, which involved folding of the second stratigraphic sequence, including the Middle Cambrian Nelson Limestone. (3) A post-Permian event (225 m.y. or less), perhaps mid- Mesozoic, which involved folding of the third sequence, including Permian coal beds. Ford has recently defined this disturbance as the Weddell Orogeny (Schmidt, written communication). 69 The apparently close relationship between the gneiss of Serpan Peak and the supposed granite body allows three possible interpreta­ tions: (1) the gneiss is Precambrian crystalline basement, brought to the surface along a fault between the granite and the Patuxent Forma­ tion; ( 2) the gneiss is a mafic border phase, genetically related to the granite pluton; or (3) the gneiss is a zone of chemically altered sed­ imentary rock at the contact of the granite (Schmidt, written communica­ tion) , Schmidt (written communication) has suggested that the second interpretation is most probable: that the gneiss represents a foliated "protoclastic" border phase of the Serpan granite. Chemical analyses of the granite and gneiss are compared in Table 14. The gneiss samples contain less SiOg, Na 2O f and K2C>2 than the granites. However, the gneiss samples contain more AlgO^, FegO^, MgO, and CaO than the granites. It is not yet possible to determine the reason for this differ­ ence in chemistry, if in fact the granite and gneiss are co-magmatic. Another possibility exists: that the more mafic character of the gneiss is a result of partial assimilation of the adjacent Patuxent Formation. No chemical analyses of the Patuxent Formation are available at this time to test this possibility. Besides the granite-gneiss relationship, there may be a genetic relationship between the Serpan Granite and the volcanics of the Gambacorta Formation. Schmidt and others (1965) suggested the pos­ sibility that the granite is older than the Elliott Sandstone. If this is true, the granite may intrude the Gambacorta Formation, underlying the 70 Table 14: Chemical Analyses of the Serpan Granite and the Serpan Gneiss, Neptune Range, Pensacola Mountains (from Schmidt, written communication)

Serpan Granite Serpan Gneiss 432 433 427 431

S i0 2 75.96 75.25 55.41 69.86 12.87 12.92 16.71 14.37 A12°3 3.32 Fe2°3 .50 .55 .85 FeO 1.03 1.27 4.97 2.21 MgO .09 .09 3.54 1.06

CaO .59 .65 6.76 1.41 N a2° 3.29 3.26 2.99 3.50 k 2° 4 .7 8 4.92 2.60 4.39 h 2°+ .50 .59 1.38 1.21 h 2° - .08 .09 .04 .07

T i0 2 .10 .12 1.30 .50

.01 .01 .49 .15 P2°5 MnO .04 .05 .15 .08 O O .02 .03 .05 .17 to Cl .01 .02 .02 .03

F .02 .02 .16 .06 Subtotal 99.89 99.84 99.89 99.92

Less O .01 .01 .07 .04

Total 99.88 99.83 99.82 99.88 71 Elliott Sandstone. The Gambacorta volcanics may then represent the beginning of an orogeny in Cambro-Ordovician time that ended with the intrusion of the Serpan Granite. Table 15 lists chemical analyses of samples of the Gambacorta Formation. Comparison with Table 14 shows a close similarity between these analyses and those for the Serpan

Granite. If these two units are indeed co-magmatic, they could have 87 86 identical initial Sr /Sr ratios. This hypothesis was tested and the results are discussed in the later section, Age Determinations (Summary). Lamprophvre dikes. Several small dikes of porphyritic olivine- clinopyroexne-biotite lamprophyre a few cm to 1 m wide cut the Patuxent Formation in the Patuxent Range. Brecciation, viscous-flow structure, and lack of wall-rock alteration suggest that the dikes were intruded at relatively low temperatures. Potassium-argon dates of 219, 233, and 244 m.y. - 5% on biotite from these dikes have been reported by Schmidt and Ford (1969). Dufek Intrusion. Ford and Boyd (1968) have described the large stratiform mafic intrusion that makes up the Dufek Massif and most of the Forrestal Range. The intrusion consists of pyroxene gabbro inter­ layered with minor anorthosite and pyroxenite and capped with granophyre. The intrusion is exposed in two partial, nonoverlapping stratigraphic sections each about 2 km thick, one in the Dufek Massif and one in the

Forrestal Range. The estimated thickness of the intrusion is 7 km and the known 2 areal extent is 8,000 km ; magnetic anomalies indicate a much greater extent unexposed. Layering in the Dufek Massif is tilted gently Table 15: Chemical analyses of the Gambacorta Formation, Neptune Range, Pensacola Mountains (from Schmidt, written communication)

Sample 351 294 292 293 348 349 350

Si02 74.10 73.71 76.98 76.88 74.71 73.27 73.71 12.45 14.12 12.06 11.95 12.68 12.63 12.65 A12°3 1,52 1.22 1.08 .94 1.82 Fe2°3 1.31 .85 FeO 1.24 1.40 .27 .38 1.15 2.20 .61 MgO .39 .38 .17 .08 .44 .54 .49 CaO 1.15 1.79 .19 .55 1.31 2.05 1.38 Na2° 3.79 .91 2.21 3.31 3.47 3.36 3.33 k 2o 3.50 3.64 5.88 4.75 3.72 3.34 3.32 h 2o + .85 1.67 .52 .32 .89 1.08 1.29 h 2° - .04 .27 .08 .05 .05 .05 .12 Ti02 .26 .11 .11 .28 .24 .34 ,23 .02 .02 .02 .07 .05 .02 P2°3 .06 MnO .06 .05 .01 .02 .05 .08 .07 c o 2 ,59 .15 .01 ■ .02 .27 .07 .75 Cl .00 .02 .01 .01 .00 .01 .01 F .03 .02 .02 .03 .03 .08 .04 Subtotal 99.79 99.78 99.76 99.76 100.00 100.01 99.84 Less O .01 .01 .01 .01 .01 .03 .02 Total 99,78 99.77 99.75 99.75 99.99 99.98 99.82 73 southeastward. In the Forrestal Range, the layering forms a broad syncline. Neither the base nor the top are exposed, but a post-Permian age is indicated by metamorphic effects on nearby Permian carbonaceous beds.

Structure Figure 24 is a diagrammatic geologic cross-section of the central Neptune Range {Schmidt and others, 1965) that illustrates the structure of the Pensacola Mountains,with the exception of the Dufek Massif. The structure of the Neptune Range can be divided into three * parts coinciding with the three stratigraphic sequences, each bounded above by an angular unconformity. The oldest sequence consists of the Patuxent Formation. These rocks are mostly isoclinally folded with nearly vertical axial-plane cleavage that strikes north in the Neptune Range, northeast in the Patuxent Range. The second sequence consists of the Nelson Limestone, the Gambacorta Formation, and the Wiens Formation. Open, sinuous folds are symmetrical with wave lengths of about 9.6 km. Some smaller folds are disharmonic, asymmetrical, and locally overturned toward the west. Fold axes trend northerly and plunge gently to the south. The Beacon rocks of the third sequence have likewise been deformed into broad open folds, trending northerly in the central Neptune Range and in the Forrestal Range. The rocks of the third sequence dip gently east on the plateau of the eastern Neptune Range and are horizontal in the northeastern part. Along a major structural discontinuity, 74

DIAGRAMMATIC GEOLOGIC CROSS SECTION ww Appro«lm«t» pr««nll u r f . c t (Cenlrnl Neptuna R ange, vldnlly ol B3* 30‘ South)

I

Hcrfjonlat and vertical scale • Mil** Number* ralar to rock unit* Unit P I* hppabyaaa) shown In columnar s*£Uon rhyolll* porphyry 12 Kilometer*

Fault Arrows show relative direction ol movement liociintlfr folded bedding and nearly vertical ailal-piin* cleavage Indefinite contact between erantt* and eonteel-matamorpheaad Patuient Formation Bedding surface* Sheared end JolUJed rock

Figure 21|. Structure cross section of the Reptune Range, Pensacola Mountains (from Schmidt and Ford, 1969). 75 probably a fault zone, in the west central Neptune Range, the rocks of the third sequence are nearly vertical or slightly overturned to the west

(Schmidt and others, 1965). The Dufek Intrusion has been uplifted along high-angle faults bordering the southeastern edge of the Filchner Ice Shelf. A similar fault zone of probable large displacement may be the reason for the present height of the Pensacola Mountains (Schmidt and Ford, 1969).

Age Determinations

An attempt was made to date seven rock units of the Pensacola Mountains: the Patuxent Formation; the diabase silis, the basalt flows, and the felsic flows interlayered with it; the Gambacorta Formation; and the Serpan Granite and Gneiss. These units are part of the first and second stratigraphic sequences and have been folded at least twice. The Patuxent Formation has been metamorphosed to the chlorite grade and all the other units have been altered to varying degrees.

Gambacorta Formation Eleven samples, representing four members (see Table 13) of the Gambacorta Formation have been analyzed.for dating. Two addi­ tional samples have been included: (1) 294, a rhyolite breccia at the base of the Elliot Sandstone that is part of the Beacon Supergroup sequence above the Gambacorta and (2) 356, a hypabyssal rhyolite porphyry from a plug at Pope Nunatak in the north-central Neptune Range. The analytical data are summarized in Table 16. Table 16: Rb and Sr Analytical Data for the Gambacorta Formation 76

Sample Rb Sr Rb 87/S r86

290 262.6 168.4 4.525 0.7311 261.1 169.0 4.478 0.7319 avg. 261.9 168.7 4.502 - 0.023 0.7315 - 0.0008 291 115.2 241.5 1,381 0.7207 - 0.0009 114.2 244.4 1.353 • 114.7 243.0 1.367 - 0.014 292 130.0 166.0 2.270 - 0.028 0.7214 - 0.0018 293 144.3 136.5 3.064 - 0.038 0.7286 - 0.0012 294 140.6 132.2 3.085 - 0.038 0.7292 - 0.0014

348 131.1 121.2 3.136 - 0.039 . 0.7291 - 0.0012 349 121.7 170.5 2.066 - 0.026 0.7221 0.7211 0.7216 - 0.0010 350 128.5 107.3 3.474 ± 0.043 0.7333 - 0.0013 351 106.3 112.6 2.736 - 0.034 0.7286 - 0.0010 356 136.8 132.7 2.987 - 0.037 0.7274 - 0.0008 389 158.7 83.90 5.498 - 0.069 0.7495 - 0.0008 390 135.8 193.2 2.035 - 0.025 0.7223 - 0.0007 391 94.57 173.1 1.582 - 0.020 0.7160 - 0.0005

aby isotope dilution ^corrected for isotope fractionation by assuming Sr8 6 /sr88 = 0.1194 77 The Gambacorta Formation is probably Middle to Late Cambrian in age, as indicated by stratigraphic relationships. The Hawkes member of the Gambacorta conformably overlies the Middle Cambrian Nelson Limestone in many places. The Gambacorta Formation is well exposed between the Nelson Limestone and the Elliot Sandstone, which is probably Ordovician in age (Schmidt, written communication). The Rb and Sr analytical data are plotted in an isochron diagram in Figure 25. Clearly, the points are scattered and do not fit a single isochron. That this scatter is real is indicated by the precision of the measurements; samples 290 and 291 were analyzed in duplicate and in 8 7 86 both analyses the Rb /Sr ratios differed by less than 2%. Duplicate R7 Rfi measurements of the Sr /Sr ratio in samples 290 and 349 show dif­ ferences of about 0 . 1%i There might be several reasons for such nonlinearity: (1) differ­ ent degrees of contamination by crustal rocks; ( 2) different initial 8 7 86 Sr Sr ratios; (3) the lack of whole-rock closed systems due to metamorphism and alteration since deposition; and (4) the fact that different units of the Gambacorta might be of significantly different age. Contamination by surficial rocks on which the volcanic flows were extruded must be considered a possibility. Sample 291 from the Lower Gambacorta member, for example, is probably contaminated by the underlying Nelson Limestone. Other samples, however, cannot be explained in this way. Although the Hawkes member is commonly intensely altered and contaminated with calcite near the Nelson Lime­ stone, the samples selected by Schmidt were supposedly not from such disturbed and altered outcrops. A a B 0

0290 . 0 3510^8^294, 343 '356

390, 2 9 2 0 T = 568 ±39 n.y.

(Sr'39/Sr36)0 = 0.7052 *0.0015

0

o\

Rb 8 7 / s r 8 6 * 7 -j Figure 25. Isochron diagram for the Gambacorta Formation, Neptune Range CD Thin-section analyses of the samples of the Gambacorta Forma­ tion, however, show extensive contamination by xenoliths in varying degrees of alteration (Shultz, written communication). Sample 349 from the Hawkes member, for example, has small xenoliths of arenaceous limestone and fine-grained graphic granite. Xenoliths of crustal rock 87 would be enriched in Rb and radiogenic Sr ; their presence in random fashion and in various lithologic types could produce the scatter shown in Figure 25. The second possibility of explaining the observed scatter is that the flows and pyroclastic units are not co-magmatic. This situa­ tion could occur in two ways: ( 1) the flows and pyroclastics originated at the same time, but from different magma sources, some perhaps containing more crustal-derived matter than others and thus having 87 Rfi higher Sr /Sr ratios (2) the units may be of different age, which is the fourth possibility for producing the observed scatter. Both of these conditions would be indicated by isotopic homogeneity of the initial 87 Rfi Sr /Sr ratios within each stratigraphic unit. Two units are repre­ sented by more than one sample. Samples 290, 390, and 389 from the Red-Brown Member are only co-linear if 290 is omitted (isochron B in Figure 25). The six samples from the Hawkes Pyroclastics (292, 293, 348, 349, 350, 351) define isochron A, but are also not co-linear. The nearly identical positions of isochrons A and B and the scatter of points defining isochron A seem to indicate that the Red-Brown and 87 86 Hawkes Members do not have characteristic initial Sr /Sr ratios. The third suggested possibility is varying degrees of alteration during the several metamorphic events since deposition of the Gamba­ corta Formation in the Cambrian. All thin sections described by Schultz show alteration effects. Sample 290 is a greatly altered rhyolite, show­ ing abundant hematite (as do many other samples), which suggests iron metasomatism. Alteration effects common in other samples are: (1) embayed and rounded quartz grains (2) K-feldspar altered to clay, epidote, and sericited, and replaced by hematite (3) plagioclase par­ tially altered to sericite and epidote (4) anphibole altered to chlorite,

sphene, and carbonate. Together with contamination by xenoliths of crustal rocks, metamorphism provides ample reason for the scatter shown in Figure 25. If an isochron is fitted to all thirteen samples the calculated date is 493 - 53 m.y. This date is compatible with stratigraphic rela­ tionships, but the poor degree of fit is unacceptable. Isochron A is calculated for twelve points, 290 is omitted, and indicates a date of

j . 0 7 OC X 568 - 39 m.y. with an initial Sr /Sr ratio of 0.7052 - 0.0015. If a procedure is followed like that described in the "isochron analysis" section, it may be possible to reduce the error of the age determination and to indicate a more realistic variation of the initial 87 Rfi Sr /Sr ratio. Samples from the Hawkes Member and the Red-Brown Member (except 290) define isochrons B and C respectively (isochron B is not drawn, but is very close to A). Samples 292, 356, and 391 define isochron D. Isochron B indicates a date of 5 72 - 81 m.y. with an initial Sr 87 /Sr 86 ratio of 0.7051 - + 0.0032. Isochron C indicates a date of 81 563 - 2 m.y. and an initial Sr^/Sr^ ratio of 0.7063 - 0.0001. Iso- + 87 86 chron D produces a date of 580 - 5 m.y. and has an initial Sr /Sr

-L. ratio of 0.7032 - 0.0001. These three isochrons are parallel, within the limits of error, to isochron A, defined by all the samples {except

290). All of these dates are consistent with the stratigraphic age of the Gambacorta Formation and account for 12 of the 13 samples; the highly altered sample, 290, does not fit an isochron that is compatible with stratigraphic information. By this method the best possible radio- metric determination of the age of the Gambacorta Formation is a weighted average of the dates of isochrons B, C, and D: 573 - 81 m.y. The range 87 Rfi of initial Sr /Sr ratios is from 0.7031 to 0.7083. In this case the method of multiple isochrons has not reduced the error of the age determination. The error of isochron A fitted through all the points (except 290) is 7%; the error of the weighted average 87 86 isochron is 14%. The range of initial Sr /Sr ratios for the two methods is only slightly different, 0.7037 to 0.7067 for isochron A and 0.7031 to 0.7083 for the weighted average isochron. Separation of the Gambacorta Formation samples on the basis of stratigraphy is not suf­ ficient to reduce the error of the age determination. In summary, the rocks of the Gambacorta Formation do not form a single isochron because they have not remained closed systems to Rb and Sr since their extrusion as lava and pyroclastics. Contamination has probaly occurred by inclusion of xenoliths of crustal rocks or post- depositional alteration, or both. The best estimate of the age of these “f* volcanics is 568 - 39 m.y. < 82 Serpan granite and gneiss Eight samples of the Serpan gneiss from Serpan Peak in the north­ east Neptune Range were analyzed for dating. The analytical data are summarized in Table 17 together with data for two specimens of Serpan granite from moraine deposits near Serpan Peak. The gneiss samples vary from a dark dioritic phase with abun­ dant hornblende, sphene and chloritized biotite to a leucocratic phase in which the biotite is also altered to chlorite. One of the granite samples is a white biotite granite, the other is a red variety. The data for the Serpan gneiss are plotted in an isochron diagram in Figure 26. As with the Gambacorta Formation no single linear array is apparent. An isochron fitted to all eight samples indicates an age of 674 - 55 m.y. with an initial Sr®^/Sr^ ratio of 0.7054 - 0.0006, This isochron has not been drawn on Figure 26 because the scatter of the data suggests that multiple isochrons may be more accurate representa­ tives of the age of these rocks. If, as Schmidt has suggested, the gneiss represents a border phase of the Serpan Granite, then the chemical differences between the two shown in Table 14 indicate that assimilation of country rock (prob­ ably the Patuxent Formation) has occurred. This assimilation may be responsible for the scatter of points on the isochron diagram. If the gneiss samples are assumed to be the same age, then parallel isochrons fitted to subsets of the data will reduce the uncertainty in the cal- 87 86 culated age due to the presence of more than one initial Sr /Sr ratio. 83 Table 17: Rb and Sr Analytical Data for the Serpan Granite and Gneiss, Neptune Range

Sample Rb Sr R b f/S r 86 (Srf/Sr86)b (ppm)a (ppm)a - error - 2

Serpan Granite 432 280.2 66.6 11.64.- 0.19 0.7933 - 0.0030 433 266.2 60.9 11.87 - 0.18 0.7934 - 0.0026 USGSd 2 7 8 .0C 5 4 .4C 14.74 0.8154 Serpan Gneiss

424 161.2 452.4 0.9623 - 0.0149 0.7153 0.7153 0.7153 - 0.0002 425 156.6 314.5 1.347 ± 0.021 0.7153 0.7161 0.7157 - 0.0008 426 87.2 823.2 0.2842 - 0.0044 0.7078 0.7078 0.7078 - 0.0002 427 98.4 654.7 0.4096 - 0.0066 0.7087 t 0.0022

428 164.0 440.6 1.020 - 0.016 0.7130 - 0.0018 429 89.2 628.1 0.3826 - 0.0061 0.7094 - 0.0014 430 205.5 175.2 3.155 - 0.048 0.7304 0.7318 0.7311 - 0.0014 431 170.6 397.3 1.15.7 - 0.018 0.7162 - 0.0017

a By x-ray fluorescence

^Corrected for fractionation by assuming Sr®®/Sr 88 = 0.1194

cBy isotope dilution ^Schmidt, written communication 0.730

0.720

0.710 T = 525 ±1 5 ra.y. (Sr87/Sr86)0 = 0.70^7-0.7086

0.700 1.0 1.5 2.0 2.5 3-0 Rb87 / S r 66 Figure 26. Isochron diagram for the Serpan Gneiss, Neptune Range, Pensacola Mountains.

00 4^ 85 Isochron A in Figure 26 is defined by samples 424, 430, and

431. It indicates a date of 516 - 14 m.y. with an initial Sr^^/Sr ^6 ratio of 0.7084 - 0.0002. Isochron B, defined by samples 425, 426, 427, and 428, indicates a date of 531 -5 m.y. with an initial Sr^/Sr^ ratio of 0.7057 -4 0,0. The best estimate of the age of these rocks is a weighted average of these two isochrons: 525 - 15 m.y. with a range of initial Sr^/Sr®^ ratios of 0.7057 to 0.7086. Analytical data for the Serpan Granite have been plotted in Figure 27. The two samples of granite analyzed at The Ohio State Univ­ ersity (432, 433) are combined in this plot with the granite sample dated by the U.S. Geological Survey (U.S.G.S.). An isochron fitted to these 4 87 86 three samples indicates an age of 530 - 34 m.y.; the initial Sr /Sr ratio is 0.7064 - 0.0061. This age is identical within the limits of analytical error to the model age calculated by the U.S.G.S. for one sample of the Serpan Granite. The large uncertainty in the initial 87 ftfi Sr /Sr ratio is due to the position of the data points, far from the 87 flfi Sr /Sr coordinate and because the two samples analyzed at O.S.U. plot very close together, but are not identical, producing some un­ certainty in what otherwise would be a two-point isochron. The age calculated for the Serpan Granite is also identical within the limits of error to the age of the Serpan Gneiss. The initial 87 8fi Sr /Sr ratio of the Serpan Granite is within the range of initial ratios calculated for the Serpan Gneiss. These results, together with the field relationship, support Schmidt's suggestion that the gneiss and granite are co-magmatic. A pooled isochron, Figure 28, using all 8 6

0.82

0.73

Sr' Sr

T 530 ^34 m.y (Sr87/S r06)o - 0.7064

=t0.006l 0.70 0 5 10 15

Figure 27. Isochron diagram for the Serpan Granite, Weptuna Range. 0.820

Serpan Granite

0.800

Sr'

0.760

T - $55 ± 2 b m .y. (Sr87/S*86)0 = 0.7065 ±0.000$

0.720 Serpan Gnelsa

10 12

Figure 28. Isochron diagram for the Serpan Granite and Gneiss, Neptune Range. 8 8 eleven samples yields probably the best estimate of the age of the + 87 86 Serpan Granite and Gneiss: 555 - 26 m.y., with (Sr /Sr ) =

0.7065 - 0.0005.

Felsic flows and plugs Nine samples of felsic flows and plugs deposited with and in­ truded into the Patuxent Formation in the Neptune Range have been anal­ yzed for an age determination. Analytical data for these samples are listed in Table 18. Three samples are rhyolites collected from Gorecki nunatak in the Schmidt Hills (352, 354, 358). They occur in a large block that does not show the otherwise pervasive isoclinal'folding of the Patuxent Formation, but are in a massive breccia containing limestone fragments that are anomalous to the Patuxent Formation. Five samples are from the Williams Hills. Samples 434, 435, 353, and 355 are rhyolites which occur near vertical dips in isoclinally folded Patuxent Formation. Specimen 35 7 is a felsic welded tuff and is from an outcrop which does not show folding. The analytical data for these felsic rocks are plotted in Figure 29. It is clear by inspection that these samples do not define a single isochron. However, four samples, 354, 357, 358, and 434, do define an isochron which is labeled A. It indicates an age of 1210 - 76 m.y. and an initial Sr^/Sr®^ ratio of 0.7052 - 0.0008. This age is compatible with the field evidence that the Patuxent Formation is older than Cambrian. In fact, because the felsic flows are interbedded with the sediments, the age of the flows is a good estimate of the time of 89 Table 18: Rb and Sr Analytical Data for Felsic Flows and Plugs of the Patuxent Formation, Neptune Range

Sample Rb Sr Rb 87 /S r86

352 78.99 299.4 0.7482 * .0157 0.7158c 76.43 302.1 0.7122 avg. 77.71 300.8 0.7126 - 0.0008

353 264.2 111.8 6.903 - .029 0.7567 264.5 111.0 0.7546 264.4 111.4 0.7553 0.7555 - 0.0024 354 36.00 318.2 0.3276 - .0041 0.7111 - 0.0010

355 116.4 81.23 4.094 - .071 0.7444 113.9 82.27 0.7439 , 115.2 81.75 0.7442 - 0.0006

357 2.7c 42.17 0.1299 - .0384 0.7088 1.82 38:80 0.7052 . 1.82 40.49 0.7070 - 0.0036

358 102.6 484.4 0.6136 - .0077 0.7145 - 0.0014

434 4 4 .8d 116.5d 1.048 - .017 0.7231 - 0.0008 435 1.5d 81.6d 0.0557 - .00464 0.7181 0.7161 0.7174 - 0.0023

aBy isotope dilution unless otherwise noted. b 86 88 Corrected for fractionation by assuming Sr /Sr = 0.1194 cNot included in the average. ^By x-ray fluorescence. 0.750

Sr 0.720 U ) T = 1 2 1 0 =t76 m .y.

(SrQ7/Sr86)0 = 0.7-052 ±0.0008 0.710

(Sr87/sr86)Q = 0.7072-0.7172 0.700

RbQ7/Sr86

Figure 29. Isochron diagram for the felsic flows of the Patuxent Formation, Ke ptune Range. vo o 91 deposition of the Patuxent Formation. Four samples do not fit isochron A. Taken together, these sam­ ples define an isochron which produces a date of 585 - 92 m.y. with an initial Sr^/Sr^ ratio of 0.7026 - 0.0041. The high initial ratio and the probability that the felsic flows of isochron A are 1210 m.y. old suggests that this date is a reset date due to a metamorphic event, perhaps during the Ross Orogeny. The reasons why the four rocks of isochron A appear to have escaped the effects of a later metamorphic event are not clear. Geog­ raphy does not seem to have been a factor. Two of the samples of isochron A are from the Schmidt Hills (354, 358) and two others are from the Williams Hills (353, 434). The degree of metamorphism may have been a factor; three of the samples of isochron A are from outcrops which Schmidt noted as not showing the typical isoclinal folding of the Patuxent Formation (354, 358, 357). However, sample 434 was folded and sample 352, although not folded, does not lie on isochron A.

The large error of the 5 85 m.y. date and the scatter of the data suggest that the method of multiple isochrons may reduce this uncer­ tainty. Isochron B is constructed through the points for samples 352 and 353. It yields a date of 500 - 8 m.y. and an initial ratio of 0.7074 - 0.0002. It is parallel to the 585 - 91 m.y. isochron within the limits of error. Isochron C is defined by 355 and 435 and is closely parallel to isochron B. It indicates a date of 475 - 2 m.y. and an initial ratio of 0.7171 - 0.0001 . The weighted average date for these + 87 86 two isochrons is 488 - 6 m.y. The range of initial Sr /Sr ratios is 92 from 0.7072 to 0.7172. This result is taken as the best date for the four reset samples. It has a significantly lower associated error than the combined isochron and indicates better the scatter of the data be- 87 86 cause it indicates a larger range of the initial Sr /Sr ratio. In summary/ the felsic flows deposited with the Late Precambrian Patuxent Formation may be as old as 1210 - 76 m.y. however, a Cambro-Ordovician period of volcanism and granitic intrusion has reset some of the felsic flows to the time of this orogeny. The best estimate of this Cambro-Ordovician event, using data from the felsic flows, is

488 - 6 m.y.

Patuxent Formation Eleven samples, of metasedimentary rocks from the Late Pre­ cambrian Patuxent formation were analyzed: 2 subgraywackes, 5 silt- stones and shales and 4 slates. These analyses are listed in Table 19n All of these rocks are from the Patuxent Range, unlike the other rock units dated which are from the Neptune Range. The Patuxent Formation samples were chosen by Schmidt from outcrops in the Patuxent Range so as to be relatively free from alteration by intrusives (Schmidt, personal communication). The rocks are all from different outcrops, scattered throughout the range. The Patuxent Formation in the Neptune Range contains abundant diabase and basalt, plus the felsic flows and plugs discussed above. In the Patuxent Range, however, the only intrusions are a few small Lamprophyre dikes (232 m .y.), small, probably late Precambrian diabase sills 40 km from a sample site, and a small late Precambrian or early 93

Table 19: Rb and Sr Analytical Data for the Patuxent Formation, Patuxent Range

Sample Rb Sr Rb 87 /Sr86 {Sr87 /Sr86)b (ppm)a + (ppm).,a - error - 2 <^

436 195.0 103.6 5.103 - 0.079 0.7430 - 0.0019 437 184.8 65.2 7.704 - 0.118 0.7639 - 0.0026 438 102.9 193.2 1.452 - 0.023 0.7253 - 0.0025 439 228.7 50.0 12,498 - 0.193 0.7815 - 0.0038 440 106.8 98.4 2.936 - 0.046 0.7315 0.7304 avg. 0.7309 - 0.0011 441 256.5 87.1 8.009 - 0.123 0.7596 - 0.0020 442 225.5 36.6 16.735 - 0.261 0.8083 0.8091 0.8087 - 0.0008

443 - - 1.671 - 0.029 0.7272 - 0.0026 444 153.6 176.0 2.471 - 0.038 0.7328 ± 0.0016

445 - - 2.253 - 0.035 0.7283 - 0.0036 446 115.5 229.2 1.369 - 0.021 0.7225 - 0.0022

aBy x-ray fluorescence. b 86 88 Fractionation corrected by assuming Sr /Sr = 0.1194 94 Paleozoic rhyolite porphyry 60 km from a sample site. Hopefully, there­ fore, these samples of the Patuxent Formation would have a radiometric age compatible with their stratigraphic position unconformably beneath the Middle Cambrian Nelson Limestone. They have, however, been

regionally metamorphosed. The analytical data for the Patuxent Formation are plotted in an isochron diagram in Figure 30. Two linear arrays are formed. The dis­ tinction as to which line a sample is on does not have any apparent basis in lithology or geographic location. Samples 437 and 444 form isochron A, for which a date of 436 - 124* m.y. has been calculated; the

0 7 pC * initial St /Sr ratio is 0.7173 - 0.0006. The remaining nine samples form an isochron/ labeled B, which produces a date of 402 - 4 m.y.4* with an initial Sr®^/Sr^ ratio of 0.7146 - 0.0004. A combined isochron with all eleven samples indicates a date of 395 - 10 m.y., identical within the limits of analytical error to the date of isochron B. If sam­ ples 437 and 444 are considered anomalous, isochron B can be con­ sidered to be the best determination of a radiometric date on the Patuxent Formation. This date is not an indication of the time of deposition, but is a reset date produced by the last metamorphic event which affected the Patuxent Formation in the Patuxent Range.

Basalt and diabase It was hoped that analysis of the basalt flows and diabase sills deposited with and intruded penecontemporaneously into the Patuxent Formation would permit the accurate dating of the associated sediments. To this end, six diabase samples from the Schmidt Hills and four basalt 0.800 -

0.780

■ 0.760 Sr

Sr

0 .7 4 0 T • 402±£> m.y. . (Sr67/Sr86)0 = 0.7146 ±0.0004

0.72C

0.700 10 12 Hb87/Sr86

Figure 30. Isochron diagram for the Patuxent Formation, Petuxent Range. ^ vn 96 samples from the Williams Hills were analyzed (these outcrop areas are in the western Neptune Range). The analytical data are listed in Table 20 and plotted in an isochron diagram in Figure 31. 87 86 As expected for such basic rocks, the values of Rb /Sr ratios are quite low (less than 0.7 overall, less than 0.25 for most samples) and their range is small. No apparent isochrons are formed; the samples are not dateable because of low Rb/Sr ratios and insufficient enrichment 87 in radiogenic Sr If the rock systems have not been re-homogenized in Rb and Sr since their original formation, it is possible to calculate maximum and minimum dates of origin. Isochron A in Figure 31 has been drawn as a minimum age limit for the diabase sills and isochron B was drawn as a maximum age limit. Between these two slopes are all possible isochrons for these data, assuming that sample 421 is not anomalous. One of this set of isochrons may indicate the true date of origin for the diabase s ills . Isochron A indicates a minimum date of 760 m .y. with an initial

■ 0 7 Q C Sr /Sr ratio of 0.7067. Isochron B yields a maximum date of 1267

07 OC m.y. and an initial Sr /Sr ratio of 0,7020. A good estimate of the age of these rocks is obtained by isochron C, which is defined by sam­ ples 418, 419, 420, and 421, all from the same sill. The date produced ■ p7 oc from this calculation is 778 - 59 m.y. The initial Sr /Sr ratio is 0.7065 - 0.0003. The conclusion that the diabase sills are Precambrian is compatible with the stratigraphic age of the Patuxent Formation. 97 Table 20: Rb and Sr Analytical Data for Diabase and Basalt of the Patuxent Formation, Neptune Range

Sample Rb Sr Rjb87 /Sr86 (Sr87 /Sr86)b (ppm)a (ppm)a - error ± 2 .

Diabase 418 12.1 198.0 0.1768 - 0.0030 0.7079 - 0.0013

419 8.0 203.6 0.1131 - 0.0068 0.7077 - 0.0014 420 2.7 223.8 0.0342 - 0.0011 0.7071 - 0.0011

421 66.1 273.9 0.6647 - 0.0107 0.7138 - 0.0013

422 9.4 212.9 0.1208 - 0.0030 0.7061 - 0.0019 423 23.4 267.4 0.2370 - 0.0058 0.7062 - 0.0020 Basalt 414 1 0 0 . 3C 0.1830 - 0.0070 0.7078 - 0.0011 0.1371 - 0.0081 0.7079 i 0.0018 415 iO .ic 207.6 c 416 13.0 244.1 0.1415 - 0.0041 0.7061 - 0.0024

417 11.1 194.5 0.1655 - 0.0114 0.7077 - 0.0016

aBy x-ray fluorescence unless noted otherwise. u 86 88 Fractionation corrected assuming Sr /Sr = 0.1194 °By isotope dilution. 98

0.712

0.710

0.708 Sr' !tf W /

0.706 lf.220& i| 16 J3 \\2 y

Best Estimate of T la Isochron Cr 779 ±59 m.y. (Sr87/Sr96 )0 = 0.7065 ±0.0003 0.702

o .i 0.2 0 .30.4 0 .5 0.6 0 .7 Rb37/Sr86 Figure 31. Isochron diagram for diabase and basalt of the Patuxent Formation, Neptune Range. 99

There is some indication that the diabase samples have retained 07 Of. some original stratigraphic characteristics with regard to the Sr /Sr ratios. Samples 418, 419, 420, 421 all come from the same sill (60 m thick) at Gorecki Nunatak. They are numbered in order, from the base to 15 cm below the sill top. Schmidt noted that there was no mega- or micro-evidence of contamination with the surrounding Patuxent Forma- 87 86 tion, but sample 421 may owe its relatively high Sr /Sr ratio to the nearness of the contact and resulting assimilation effects. The remain­ ing two diabase samples, 422, 423 are from the interior of a sill 80 to 87 86 110 m thick, at Nunatak #10 and appear to have different Sr /Sr ratios from the Gorecki Nunatak samples. Unfortunately, this inter­ pretation is merely conjecture and cannot be used to support the belief that the age estimate is reliable. The four basalt samples are all from different outcrops in the Williams Hills. Clearly, inspection of Figure 31 shows that the basalt flows do not form an isochron.

Summary Age determinations on two igneous units which are part of the Patuxent Formation have indicated dates which are compatible with the Precambrian stratigraphic age of the Patuxent Formation: (1) Four samples of felsic flows are dated at 1210 - 76 m.y. (2) Diabase sills intruding the Patuxent metasediments are estimated to be about 778 m.y. old.

These dates are summarized in Table 21. Prior to the deposition of the Middle Cambrian Nelson Limestone, the Patuxent Formation sediments and included igneous rocks were 100

Table 21: Summary of Age Determinations for the Pensacola Mountains

Rock Unit Age (m.y.) ( S r 87/Sr86) 3

Gambacorta Fm. plus

Serpan Granite and 4 - Gneiss 510 - 35 0.7080 - 0.0024

Serpan Granite and .1, J , Gneiss 555 - 26 0.7065 - 0.0005 Serpan Gneiss A. 516 J 14 0.7084 | 0.0002 B. 531 - 5 0.705 7 - 0.0 wt. avg. 525 - 15 0.705 7 - 0.7086 Serpan Granite 530 - 34 0.7064 - 0.0061

Gambacorta 568 | 39 0.7052 jjj 0.0015 Formation B? 572 | 81 0.7051 J 0.0032 • c. 563 - 2 0.7063 J 0.0001 D. 580 - 5 0.7032 - 0.0001 wt. avg. 5 73 - 81 0.7031 - 0.7083

Diabase A. 760 0.7067 B. 1267 0.7020 c . 778 - 59 0.7065 - 0.0003

0.7052 - 0.0008 Felsic Flows o 1210 - 76 B. 500 t 8 0.7074 J 0.0002 C. 475 - 2 0.7171 - 0.0001 wt. avg. 488 - 6 0.7072 - 0.7172

Patuxent .1. 4* Formation 402 - 5 0.7146 z 0.0004

aInitial ratio. Omitted from average and considered best estimate of the age. 1 0 1 intensely folded and subjected to mild regional metamorphism. This event has not been detected by the age measurements. The next event, in Cambro-Ordovician time, is as well recorded in the Pensacola Mountains as it is throughout most of the Transant- arctic Mountain chain: The Ross Orogeny. This orogeny in the Pensa­ cola Mountains is represented by the intrusion of the Serpan Granite, together with a mafic border phase, the Serpan Gneiss, at 555 - 26 m.y. The granitic intrusive activity may have been contemporaneous with extensive volcanism, represented by the Gambacorta Formation + which was dated at 568 - 39 m .y. The possibility, suggested by Schmidt, that the Serpan Granite and the Gambacorta Formations are co-magmatic appears to be con­ sistent with the Rb and Sr isotopic analyses. Figure 32 is an isochron diagram on which are plotted the combined data for the Serpan Granite and Gneiss and the Gambacorta Formation. The individually determined ages for the three igneous units are idential, within the limits of 87 fifi analytical error. The initial Sr /Sr ratios are also identical within the limits of error. The chemical analyses of the Serpan Granite and Gambacorta Formation listed in Tables 14 and 15 show strong similarities and also support the hypothesis that these two rocks are co-magmatic. Metamorphism during the Ross Orogeny re-set some of the felsic flows of the Patuxent Formation to a date of 488 - 6 m.y. The Patuxent Formation itself remained an open system to Rb and Sr much longer; the date of 401 - 5 m.y. for the Patuxent Formation in the Patuxent Range is the youngest event detected. However, this date may be related to 0.820

0.800

0.780

0.760

T * 510^35 n*y* (Sr87/3r86)0 = 0.7080 ±0.002^ © Gambacorta Formation 0.720 $ Serpan Gneiss 0 Sorpan Granite

0.700 0 2 6 8 10 12 Rb87/Sr86 102 Figure 3 2 . Pooled laocbron for the Gambacorta Formation, Serpan Granite, and Serpan Gneiss, Neptune Range. the different geographic locality of the Patuxent Formation samples. Unfortunately, this formation was not dated in the Neptune Range. It is possible that the Ross Orogeny persisted longer in the Patuxent Range than in the Neptune Range, 100 km away. CHAPTER IV

THIEL MOUNTAINS

Introduction

The Thiel Mountains, at latitude 85°S. and longitude 90°W ., lie about midway along the 85° S. parallel between the Ohio Range of the Horlick Mountains and the Patuxent Range of the Pensacola Mountains (see Figures 1 and 33). They were originally thought to be part of the Horlick Mountains until mapping by the Horlick Mountains traverse party in December 1959 showed that they formed a separate range. U.S. Geological Survey field parties did reconnaissance map­ ping in the Thiel Mountains in January, 1961, and from November 1961 to January 1962. The results of these investigations have been reported by Ford (1964), Aaron and Ford (1964), Anderson (1963), Ford and Aaron (1962), Ford and others (1963), and Schmidt and Ford (1969).

General Geology

The Thiel Mountains consist predominantly of a large still­ like body of cordierite-hypersthene quartz-monzonite porphyry, which is intruded by several granite plutons. In addition to the igneous rocks there are relatively minor amounts of thermally-metamorphosed clastic sedimentary rocks. Radiometric age determinations summarized by Schmidt and Ford (1969) and listed in Table 22 indicate late Precambrian

104 105

K f c s s

H O P^ta<5*i i «*=2u MOPl 911 Kb 800 P i \ Elliot Nupajak 90°—Hamfl Clif

50):r«*Bj M« Rl i 411 Kb 1 | 920 P i Ufr,rtiit 2812 910 P i 504 Kb

Moulto Escarpmen

0 20 2;0 60 80 igo Km I i_ _ i — Jd D iab ase J u r a s s i c ? OCg G r a n itic Upper Cambrian to Rock Lower Ordovician pCm C-H-Q Precambrian monzonite porphyry pCs Metasedimentary Precambrian Rocks Figure 33. Geologic map of the Thiel Mountains (from Schmidt and Ford, 1969). Table 22: Published Age Determinations for the Thiel Mountains, A ntarctica

Location M ethod & Age Reference M aterial (m .y.) A. Cordierite-hypersthene quartz-monzonite porphyry 85° 10' S. Pb-alpha: 620 - 70 2 90° 30' W . Zircon

85° 5* S. Pb-alpha: Zircon non-magnetic 630 J 70 2 m agnetic 530 - 60 2

85° 19' S. Pb-alpha: 670 ± 50 1 87° 50 ’ W . zircon B. Granodiorite

[Pb-alpha: 720 - 90 3 85° 17' S. . 1 zircon 89° 20’ W . | K-Ar: [ biotite 500 - 5% 3 ""Rb-Sr: w hole rock 648 - 85 3 85° 2' S. j Rb-Sr: 91° 37' W. H K-feldspar 646 - 85 3 K-Ar: ^ biotite 491 - 5% 3 f Rb-Sr: I whole rock 570 - 70 3 85° 27' S. j 1 K-Ar: 87° 00' W . * biotite 484 - 5% 3 Pb-alpha: zircon 470 - 50 1 Pb-alpha: 85° 17’ S. J zircon 560 - 60 1 89° 30' S. ^ K-Ar: biotite 511 - 5% 3 107 Table 22 (Continued)

Location Method & Age Reference M aterial (m .y.)

r Pb-alpha: 510 4* - 50 85° 2' S. zircon 3 91° 4 5 'W . I K-Ar; 4* 1L biotite 504 - 5% 3

References: 1. Ford, 1964. 2. Ford, etal., 1963. 3. Schmidt and Ford, 1969. • 108 to Early Paleozoic ages for the bedrock of the Thiel Mountains.

Metasediments

The oldest rocks of the Thiel Mountains are low-grade ther­ mally metamorphosed thin-bedded clastic sedimentary rocks. They crop out in the easternmost nunataks of the Thiel Mountains, and consist of spotted homfelses, impure marbles, sandstones, and siltstone. These

“beds total about 100 m in thickness and are nearly horizontal. Thin sills or flows of dacite are concordantly intercalated with the meta­ sediments. The metasediments are of unknown age, but are late Pre- cambrian or older because they are intruded by the cordierite-hypersthene quartz-monzonite porphyry for which Schmidt and Ford (1969) reported a late Precambrian age. ‘

Cordierite-Hyperstene Quartz- Monzonite Porphyry The principal rock of the Thiel Mountains is a medium-grained dark-gray cordierite-hypersthene quartz-monzonite. It crops out through- 2 out the 200 km area of the Thiel Mountains and shows no foliation or layering in most exposures. At one locality faint layering in the porphyry defines a broad, open anticline with a minimum amplitude of 500 m, and at another locality a gneissic texture may be related to magmatic flowage (Ford, 1964). About 60 percent of the porphyry is composed of large, angular phenocrysts of plagioclase and angular to rounded and embayed pherocrysts of quartz ranging from 2 to 6 mm in size. These are set in a very fine-grained holocrystalline groundmass of anhedral quartz and alkali feldspar. Smaller phenocrysts of potassium feldspar, hypersthene, 109 and cordierite are also present (Ford, 1964). Table 22 lists dates obtained by the lead-alpha method on zircons from the hypersthene quartz-monzonite porphyry. There is reasonably good agreement for a late Precambrian-Cambrian age. Although the presence of cordierite might suggest a meta-

morphic origin of the porphyry, an igneous origin is clearly indicated, according to Ford (1964) and Vance (1962), by abundant euhedral or fragmented plagioclase phenocrysts showing delicate oscillatory zoning, as well as by large quartz phenocrysts showing considerable resorption effects. There is no clear evidence, however, whether the porphyry is

volcanic or hypabyssal in nature. The very fine-grained groundmass may be the result of rapid cooling on extrusion at the surface. But many other characteristics favor an intrusive origin, perhaps as a large sill: the absence of bedding, the vertical and lateral homogeneity, the absence of individual flow units, and the uniform chemical composition. In his description of the porphyry, Ford (1964) noted the presence of granulite inclusions containing cordierite and hypersthene. He suggested that these inclusions are metamorphic xenoliths from original cordierite and hypersthene granulites (charnockites) and that their presence may explain the uniform and widespread presence of cordierite and hypersthene within this rock.

Biotlte Granite and Quartz Monzonite Several large masses of light-colored granitic rock intrude the porphyry. These have been dated as Cambrian to Early Ordovician in age (see "granodiorite" in Table 22). The granitic intrusives are granodioritic to quartz monzonitic in modal and chemical composition. 110 The intrusive character of the granitic rock is shown by contact breccia, with blocks of altered porphyry included in the granitic rock; by granite dikes and pegmatites in the porphyry; and by recrystallization effects in porphyry samples collected near the contacts (Ford, 1964).

Age Determ inations

Samples of the cordierite-hypersthene quartz-monzonite porphyry and the granitic rocks that intrude it were analyzed for dating.

Cordierite-Hypersthene Quartz- Monzonite Porphyry Four samples of the principal rock of the Thiel Mountains were analyzed for dating by the Rb-Sr whole-rock isochron method. The loca­ tions of these samples (493, 494, 495, 496) are shown on the map of the Thiel Mountains, Figure 33. Analytical data for these four porphyry samples are given in Table 23 and plotted in Figure 34. The four porphyry samples form a line whose slope indicates an age of 632 - 102 m .y., with an initial Sr^/Sr®^ ratio of 0.7086 - 0.0059. Unfortunately, the similarity of the Rb/Sr ratios of these samples does not allow the isochron to be determined with more adequate precision and leads to the large uncertainty (- 16%) of the date. The numerical value of this date is , however, in agreement with the dates reported by Schmidt and Ford (1969) shown in Table 22.

Biotite Granite and Quartz Monzonite The granitic rocks that intrude the cordierite-hypersthene quartz-monzonite porphyry are represented by two specimens of biotite granite 497 and 498, and three specimens of quartz monzonite, 499, 111 Table 23: Analytical Data for Rocks from the Thiel Mountains, Antarctica

Sample Rb Sr Rb 87 /S r 86 (Sr87 /S r86)b {ppm)a (ppm)a + - error ± 2

Cordierite-hypersthene quartz -monzonite porphyry 493 197.2 127.4 4.191 - .065 0.7447 - .0027 494 191.6 130.1 3.941 - .060 0.7427 - .0018

495 211.6 112.6 5.134 - .078 0.7544 - .0036 496 184.4 126.4 3.835 - .059 0.7433 - .0018 Biotite granite

497 153.7 154.4 2.722 - .043 0.7325 - .0017 498 185.2 155.6 3.276 - .050 0.7355 - .0026

Quartz monzonite

499 303.7 66.0 12.62 - . 20 0.7913 - .0028 500 147.2 91.9 4.386 - .069 0.7446 - .0014

501 147.5 102.3 3.930 - .060 0.7417 - .0007

aBy x-ray fluorescence. b 86 88 Fractionation corrected assuming Sr /Sr = 0.1194 112

0.760 2^495

/ T = 632*102 n.y 0.720 {Sr87/2r86)0 = 0.7086*. 0039

0.700 HbS7/Sr86 Figure 3l*. Isochron diagram for the Cord­ ierite, hypersthene quartz-monzonite porph­ yry, Thiel Mountains. 113 500, and 501. Analytical data for these samples are given in Table 23 and plotted in Figure 35. The three quartz-monzonite samples define a good isochron, labeled A, indicating an age of 409 - m.y. with an in itial Sr 87 /S r 86 ratio of 0.7194 - 0.0003. The two samples of biotite granite, 497 and 498, are very similar in Rb/Sr ratios and a reliable isochron cannot be drawn. Instead, model dates have been calculated assuming an initial Sr /Sr87 86 ratio of 0.7194. This initial ratio is the same as that for the porphyrltic quartz- monzonite, considered to be approximately contemporaneous with the biotite granite by Ford (1964), Another reason for choosing 0.7194 and an initial ratio for the biotite granites rather than 0.7100 (which is commonly estimated for granitic rocks) is that the line formed by the p n qc two points, 497 and 498, intersects the Sr /Sr coordinate at 0.7180. The model dates calculated in this way are 346 - 3 m.y. for 498 and 352 - 3 m.y. for 497. These dates are close enough to be considered one result. An average date of 349 m.y. has therefore been taken to be the best estimate of the age of the biotite granite. This isochron is labeled B in Figure 35.

Summary

The isochron age of 632 m.y. for the cordierite-hypersthene quartz-monzonite porphyry (Table 24) is in agreement with dates cal­ culated by other methods for this rock. The intrusion of this rock may indicate the presence in the Thiel Mountains of the late Precambrian Beardmore Orogeny, defined by Grindley and McDougall (1969) for the central Trans antarctic Mountains. o.soo

0.780

0.760 - fer 3? ISr86 0 .7 ^ 0

O Quartz monzonite (A) T 1;09±4 m.y* 0.720 (Sr87/Sr86 )0 0.7191; ± 0.0003 O Biotite granite (B) T 3l;9 £$% m.y. (Sr87/Sr86 )0 - 0.7191; assumed 0.700 _L X 8 10 12 lit

Rb87/Sr86 114- Figure 35- Isochron diagram for granitic rocks from the Thiel Mountains, 115

Table 24: Summary of Age Determinations for the Thiel Mountains

Rock Unit Age (Sr87/Sr86)Q - ^

Biotite Granite 497 352 3 m.y. 0.7194 (assumed) 498 346 - 3 0.7194 (assumed) avg. 349 - 5% Quartz monzonite 409 - 4 0.7194 - 0.0003 Cordierite-hyper­ 632 - 102 0.7086 - 0.0059 sthene quartz- monzonite porphyry 116 The model ages of 346 and 352 m.y. and the isochron age o f 409 m.y. determined for the granitic rocks are in agreement with their intrusive relationship into the late Precambrian porphyry. The ages of the granitic rocks are younger than the period characteristic of the Ross Orogeny, 520 to 450 m .y., and may not be related to it. CHAPTER V

NILSEN PLATEAU

Introduction

The Nilsen Plateau is part of the Queen Maud Mountains, located along the Antarctic coast near the southernmost extension of the Ross Ice Shelf as shown in Figure 36. The plateau is located at 86°30'S. latitude and 160°W. longitude, on the west side of the Amundsen Glacier, 100 km inland from the Ross Ice Shelf. The Faulkner Escarpment, the western boundary of the Nilsen Plateau, overlooks tributary glaciers leading to Scott Glacier. A systematic geological investigation of the Nilsen Plateau was carried out by an expedition of The Institute of Polar Studies, The Ohio State University, during the 1963-64 field season. The geology of the crystalline basement complex was described by McLelland (unpub­ lished manuscript).

General Geology

The Queen Maud Mountains, of which the Nilsen Plateau is a part, consist of flat-lying clastic sedimentary rocks overlying with angular conformity a basement complex made up of granitic intrusives and minor amounts of metamorphosed sedimentary and volcanic rock.

117 118

Explanation

Pliocene lo u Moralnal deposits o Pleletocene T O m No z ui Pliocene (7) to Civ Volcanic rocks Plel»toceno(?)

Jurasitc (?) Flat-lying sedimentary rocks with sills and Trlaitlef?) dikes; equivalent to Beacon rocAj o f D P b P erm ian southern Victoria Land (formations and Lower Devonian llthologles Indicated In correlation diagram)

Unconformity (Kukri Peneplain) O ------g f U p p er Deformed limestone, sandstone, and rhyollle, O J Precambrlan(7) Cl locally metamorphosed (Includes Lovorott u j I to C am b ria n Formation and Henson Marble) Q-< •. U p p er Metavolcanlc rocks (Includes Wyatt pC v Precambrlan(?) Formation and Fairweather Formation)

Metasedlmenlary rocks; melagraywacke, slate,phylllte, schist (IncludesLa Gorce pCI Formation. Duncan Formation, and < Goldie Formation) a: U pper. to Precambrlan 2 < iu(J p C m Undifferentiated melamorphlc rocks a. CL BASEMENT BASEMENT COMPLEX

Intrusive rocks, mostly granitic In composition

Precambrlan lo Ordovician

?p £ O b J Undifferentiated Basement Complex v i* ri. .

F ig u re 3 6 . Geologic 'nap of the eastern Queen Maud Mountains and Horlick Mountains (from Mirsky, 1 9 6 9 ). 118 a . 119 The basement rocks of the Nilsen Plateau are described by McLelland (unpublished manuscript). Most of the basement consists of a composite batholith composed of three major granitic plutons: the Lonely Ridge Granodiorite, the South Quartz Monzonite, and the Cougar Canyon Quartz Monzonite. Another pluton, the North Quartz Monzonite, is exposed just north of the main outcrops of the Nilsen Plateau (Figure 37 and Table 25). Minor outcrops of metamorphosed sedimentary and volcanic rocks, which have been intruded by granitic rocks of the bath­ olith, occur in scattered localities along the escarpment (McLelland, unpublished manuscript). An erosion surface with relief up to 110 feet separates the basement complex from the overlying sediments. This surface is known as the Kukri Peneplain in the Western Queen Maud Mountains and in Victoria Land. The flat-lying sedimentary sequence is 600 to 1200 m thick and is mostly of Permian age, correlative with the Beacon rocks of Southern Victoria Land. The basal unit of the sedimentary sequence is a tillite belong­ ing to the Scott Glacier Formation. The glacial deposits are overlain , by a sequence of clastic sediments which include coal and carbonaceous beds containing the Glossopteris flora (Queen Maud Formation). The sedimentary rocks are intruded by abundant diabase sills which are considered correlative with the Ferrar Dolerites of Jurassic age in Victoria Land (Mirsky, 1969). The upper beds of the youngest rocks, the Nilsen Formation (Table 25 ), may extend into the Early Triassic (Long, unpublished manuscript). Volcanic rocks of Pleistocene to Recent age occur 50 km south of the Nilsen Plateau (Mirsky, 1969). [5 3 Norrw G w r i [pTT] PltniflH-TXIHSictn STKm* — W'T« S t LIS KTCl CCUCAk CA.YO* tMNIOffirt |MV I META'/Oi.CAMlCI L-'jrtJ sou*** ouaru MtiNierttrr 123 MITAjtuiMrvK [T rU O m Y RIB6E SRAHOBIoAITf

DC.i in'»« A o r ■ v».m jM.niltx

Figure 37. Geologic nap of the Uilsen Plateau (after McLelland). Table 25: Stratigraphy of the Nilsen Plateau, Queen Maud Mountains, A ntarctica

Stratified Rocks Lithology Intrusives

Jurassic Diabase Permian to Nilsen Forma­ Sandstone, Early Trias - tion: conglomerate sic (?) Queen Maud Sandstone, Formation: Siltstone, Shale Permian coal Amundsen Formation: Sandstone Late Roaring Valley P aleozoic, Formation: Shale Permian Scott Glacier (?) Formation: T illite unconformity North Quartz Monzonite ; Cougar Canyon Early Quartz Paleozoic (?) Monzonite South Quartz Monzonite Lonely Ridge I (Metavolcanics Granodiorite Precambrian J (Metasediments

(From Mirsky, 1969, and McLelland, unpublished manuscript) 122 Metasedlmentary Rocks

The oldest rocks in the Nilsen Plateau are metasedlmentary . rocks which crop out along Black Rock Glacier (Figure 37) and are com­ posed of interbedded metagreywacke and slate. Neither top nor bottom of the 330 m section is exposed. The beds are asymmetrically folded along north-south horizontal axes with a wavelength of about 1% km (McLelland, unpublished manuscript). The metagreywacke occurs in beds h to 3 m thick and con­

sists of fine, subangular grains of quartz and albite, with minor K- feldspar and epidote, in a matrix of biotite, sericite, and a little chlorite. The beds of slate are less than 15 cm thick and consist

of very fine-grained biotite and sericite with slightly larger quartz lenses and grains of euhedral pyrite. The only exposure of the contact between metasedlmentary rocks and the granitic plutons is on the southwest side of lonely Ridge, where metasedlmentary rocks occur as xenoliths in the lonely Ridge Granodiorite, A Rb-Sr date on biotite from the lonely Ridge granodiorite indicates an age of 846 - 35 m.y. (McLelland, published manuscript) and provides a minimum date for the metasedlmentary rocks. McLelland (unpublished manuscript) and Minshew (1967) have correlated the metasedlmentary rocks of the Nilsen Plateau with the Late Precambrian La Gorce Formation in the Scott Glacier area of the Queen Maud Mountains. 123 Metavolcanic Rocks

Metavolcanic rocks crop out at the southern end of the Nilsen

Plateau, in the Cougar Canyon-Airstrip Ridge area, and also in the Black Rock Glacier area. The metavolcanic unit consists of quartz, albite, biotite, and minor K-feldspar phenocrysts 1 to 5 mm in size set in a very fine-grained groundmass of quartz, albite, and K-feldspar. The albite phenocrysts are partially altered to chlorite, sericite, and mag­ netite, and much of the groundmass is altered to sericite, epidote, chlorite, and calcite (McLelland, unpublished manuscript). An outcrop in the Black Rock Glacier area shows that the metavolcanics are discordant to the underlying metasedimentary rocks, with a chilled zone in the metavolcanics at the contact. In the same area, the metavolcanic rocks are intruded by the North Quartz Monzonite. No other contacts with granitic rocks in the area are exposed (McLelland, unpublished manuscript). Both McLelland and Minshew (1967) have correlated the meta- volcanic rocks of the Nilsen Plateau with the Wyatt Formation. The Wyatt Formation was defined by Minshew (1967) for exposure at Mt. Wyatt in the Scott Glacier area of the Queen Maud Mountains. Although the Wyatt Formation is exposed in the Wisconsin Range (Murtaugh 1969) and the Scott Glacier area in an attitude stratigraphically above the metasedimentary rocks of the La Gorce Formation, the Nilsen Plateau is the only area where the contact is exposed. 124 Igneous Rocks

Lonely Ridge Granodiorite The Lonely Ridge Granodiorite crops out in an area 2k km wide and 8 km long between Lonely Ridge and the east side of Cottonwood Canyon. The dark, medium-grained rock consists of plagioclase (An 33 to An 45), quartz, biotite, and microcline-perthite, with minor horn­ blende (McLelland, unpublished manuscript). The granodiortie has been cataclastically deformed, producing gneissose textures of narrow bands, containing augen of quartz and feldspar up to 10 mm in width. Bands of extreme deformation up to 9 m wide occur throughout the granodiorite. These blastomyIonite bands and + the gneissose foliation strike N.40°W. - 10° with an approximately vertical dip (McLelland, unpublished manuscript). Along its northern border, the Lonely Ridge Granodiorite is in fault contact with the Cougar Canyon Quartz Monzonite. However, the South Quartz Monzonite has extended apophyses into the Lonely Ridge Granodiorite. In adition, large slabs of the granodiorite are in­ cluded in the main body of the South Quartz Monzonite near their contact (McLelland, unpublished manuscript).

South Quartz Monzonite The South Quartz Monzonite forms the major part of the base­ ment complex in the southern end of the Nilsen Plateau. The rock is light-gray or greenish-gray, medium to coarse-grained, and locally porphyritic in texture. It consists of microcline-perthite, quartz, and plagioclase, with minor amounts of biotite and muscovite. The South 125 Quartz Monzonite also shows some cataclastic effects, although on a smaller scale than does the Lonely Ridge Granodiorite. On Lonely Ridge, the quartz monzonite intrudes granodiorite and metasedimentary rocks and is itself intruded by dikes of aplite and pegmatite (McLelland, unpublished manuscript). A similar quartz monzonite occurs as tabular and lens-shaped bodies within the Lonely Ridge Granodiorite adjacent to its contact with the South Quartz Monzonite. McLelland has designated this rock as a border phase of the South Quartz Monzonite, although no actual gradation between the two is known.

Cougar Canyon Quartz Monzonite The Cougar Canyon Quartz Monzonite is porphyritic, with phenocrysts of microcline-perthite up to 60 mm long in a medium to coarse-grained groundmass of quartz, plagioclase, microcline, and biotite. The groundmass shows cataclastic textures. The contacts of thus plutonic unit are not exposed, but another similar unit, McLelland's Unit U-l, intrudes a small apophysis of South Quartz Monzonite, This relationship may mean that the Cougar Canyon Quartz Monzonite is younger than both the Lonely Ridge Granodiorite and the South Quartz Monzonite (McLelland, unpublished manuscript).

North Quartz Monzonite The fourth pluton described by McLelland, the North Quartz Monzonite, is not in contact with the three plutons just described. Stocks of this quartz monzonite intrude metavolcanic rocks in the northern Nilsen Plateau, adjacent to Amundsen Glacier. The North 126 Quartz Monzonite is porphyritic, with large K-feldspar phenocrysts in a medium to coarse-grained groundmass of smoky quartz, plagioclase, and biotite. Some phenocrysts show rapakivi rims of albite. The North Quartz Monzonite is not appreciably deformed, which may mean that it is younger than the three other units of the batholith.

Age Determinations

Four rock units were analyzed for dating. These are the meta­ morphosed sedimentary rocks, the metavolcanic rocks, the lonely Ridge Granodiorite, and the South Quartz Monzonite.

Metasedimentary rocks Six metasedimentary rock samples were available for analysis.

Three of these are metagreywackes, 472, 473, and 475. Two samples are quartzites, 474 and 476. Sample 471 is a phyllite. All the samples except 471 are from the head of Black Rock Glacier (Figure 37). The phyllite, 471, is from lonely Ridge (Figure 41), where a lens of meta­ sedimentary rock occurs as a xenolith within the South Quartz Monzonite

C; and Unit 1 of the Cougar Canyon Quartz Monzonite. Analytical data for the six metasedimentary rocks are listed in Table 26 and plotted in an isochron diagram in Figure 38. Four of th ese sam ples form an isochron which indicates an age of 728 - 27 m .y. and an initial Sr®^/Sr^ ratio of 0.7117 - 0.0005. The two remaining samples, 471 and 473, define a line whose slope indicates a date of 485 m.y. with an initial ratio of 0.7173 - 0.0005. The origin of sample 471 from a xenolith within two 127

Table 26: Analytical Data for Metasedimentary Rocks from the Nilsen Plateau, Queen Maud Mountains, Antarctica

Sample Rb Sr Rb87/S r86 (Sr87/S r86)b (ppm) (ppm)a + a - error 1 2 < r

471 245.9 36.7 19.07 - .29 0.8464 -.0012 472 113.2 171.9 1.798- .028 0.7297 - .0012 473 153.3 138.4 3.012 - .046 0.7377 - .0026 474 97.7 219.4 1.208 - .019 0.7244 - .0024 475 108.9 175.3 1.703 - .027 0.7293 - .0012 476 59.8 154.0 1.074 - .017 0.7228 0.7224 avg. 0.7226 - .0004

aBy x-ray fluorescence. ^Fractionation corrected assuming Sr88/Sr88 = 0.1194. 37/Sr86) O O.flO 0.76 0.73 0.72 0 Figure Figure J*.76 33 2 ioho darm or h mtsdmnay ok, le Plateau. llsen K rocks, metasedlmentary the r fo diagram isochron . k 6 8 (Sr87/Sr86 10 )0 = 2 2 m.y. *27 720 = T 071±0.0005 0.7117± = 12

16

IS 128 129 granitic rocks suggests that it may have been isotopically rehomogen­ ized by the intrusives. The reason for sample 473's nonconformity with the age of the other samples from Black Rock Glacier is not clear. The 728 m.y. age of the metasedimentary rocks is a minimum estimate of the time of deposition of the original sediment. The iso­ chron result indicates when the metasediments were last homogenized in regard to Rb and Sr. Two samples were reset by a still later event, dated at 485 m.y.

Metavolcanic rocks Nine samples of metavolcanic rocks from the Nilsen Plateau have been analyzed for dating. The analytical data are listed in Table 27 and plotted in Figure 39. Sample 470 is from an outcrop at South Ridge, The remaining samples are from an area at the head of Cougar Canyon, about 30 km from South Ridge.

4 - An isochron fitted to all nine points yields a date of 466 - R7 + 26 m .y . with an in itia l Sr /S r ratio of 0.7179 - 0.0021. Two points, 463 and 461, lie outside the limits of error for this isochron and were omitted from a recalculated best-fit line. The isochron which results from omission of 461 and 463 indicates an apparent age of 486 - 10 m.y. with an initial Sr^/Sr®® ratio of 0.7150 - 0.0007, Because the metavolcanic rocks were regarded by McLelland as equivalent to the Wyatt Formation for which an age of 633 m.y. was reported by Montigny and Faure (1969),the isochron date of 486 m.y. for the metavolcanic rocks is regarded as a reset date. The metavolcanics may be about the same age as the metasediments, but a more accurate estimate of their age is not possible. The only igneous rock observed 130 Table 27: Analytical Data for Metavolcanic Rocks from the Nilsen P lateau, Queen Maud Mountains, Antarctica

Sample Rb Sr R b f /S r 86 (Sr87/Sr86)b

461 219.2 87.7 6.806 - .107 0.7636 - .0006 462 - - 5.628 - .087 0.7527 - .0016 463 67.1 159.3 1.147 - .018 0.7292 - .0018 464 -- 5.873 - .093 0.7554 - .0028 465 128.2 121.2 2.887 - .044 0.7344 - .0014 466 120.1 147.3 2.199 - .035 0.7307 - .0032 467 205.9 85.4 6.539 - .102 0.7583 - .0028 469 -- 6.047 - .094 0.7560 - .0022 470 - - 6.399 - .111 0.7589 - .0014

aBy x-ray fluorescence. U Q C O Q Fractionation corrected assuming Sr /Sr = 0.1194. fn Iro 0.730 0.760 0.720 0.710 iue 9 Iohc darm or h metavolcanic m the r fo diagram Isochrcn 39. Figure 0.700 oh, .isn Plateau. I.'ilsen rochs, (Sr87/Sr36)0 = 0.71^0 ±0.0007 0.71^0 = (Sr87/Sr36)0 T = 436 ± 10 m.y. m.y. 10 ± 436 = T 131 132 by McLelland to be intrusive into the metavolcanics is the North Quartz Monzonite, which he believed to be the youngest pluton in the basement complex possibly of post-Ross Orogeny origin. The lonely Ridge Gran­ odiorite, which was found to be late Precambrian in age, intrudes the metasedimentary rocks and may also intrude the metavolcanics. If this relationship is assumed to be true, it is another reason to classify the metavolcanic date of 486 m.y. as being reset. It is interesting that the metasedimentary rocks were not completely reset by later metamorphic events as the metavolcanics were. Ordinarily, sedimentary rocks, having a high clay content, are suscep- 87 tible to Rb and radiogenic Sr loss from clay minerals during metamor­ phism. Volcanic rocks, on the other hand, contain most of their Rb and Sr 87 in feldspars which are more retentive minerals. In this case, however, the sediments were originally sandstones and greywackes, high in feldspar and low in clay minerals. The one phyllite of the metasedimentary suite was reset as expected. The metavolcanics are described by McLelland as being much altered to sericite and chlorite. If during an early metamorphism (perhaps at 728 m .y.), the volcanics were recrystallized, then a later event at about 486 m.y. would more easily reset their radiometric age. The two reset metasediments also indicate this later event, at 485 m.y.

Lonely Ridge Granodiorite Seven samples of the Lonely Ridge Granodiorite were anal­ yzed for dating. The data are listed in Table 28 and plotted in Figure 40. All of the samples are from Lonely Ridge (shown in Figure 41) or nearby, an area in which McLelland (unpublished manuscript) found complex 133 Table 28: Analytical Data for the lonely Ridge Granodiorite, Nilsen Plateau, Queen Maud Mountains, Antarctica

Sample Rb Sr Rb87/S r88 (Sr87/S r86), + (ppm)a (ppm)a - error - 2

47 7 70.4 182.1 1.052 - .017 0.7206 - .0018 478 88.7 163.6 1.487 - .025 0.7242 - .0018 479 99.3 . 231.4 1.161 - .019 0.7216 ~ .0018 480 114.5 161.2 1.946 - .031 0.7284 - .0036 481 120.8 138.6 2.398 - .038 0.7300 0.7309 avg 0.7305 ± .0009

482 337.6 12.9 71.52 - 1.42 1.164 1.164 , 1.164 ± .000

483 396.5 5.4 270.7 - 6.6 2.225 1.000c 2.159 2.192 - .066

502 414.4 31.7 39.55 1.183 biotite^

aBy-x-ray fluorescence. b 86 88 Fractionation corrected assuming Sr /Sr = 0.1194 . cOmitted from average calculation.

j Analyzed by Isotopes, Inc., Westwood, N .J., (McLelland, unpublished manuscript). see i n s e r t ^

T = 611 j :17 m.y. (SrS7/Sr%) = 0.7116 i 0.0003 0.730

0.720 2.0

1 .5 - 0.710 502 W © 4 3 2

0.700 1.0 2.5 3.02.0 Hb87/Srfl6 Figure Zj.0, Xsochron diagram for the Lonely Ridge Granodiorite,

Hilsen Plateau. 134 O tooo zooo n; LOCATION

PTr-. Permian-Trlasslc seds and Jurassis sill HI; lil quartz monzonite CG: Cougar’Canyon qtz-mon. SM; South quartz nonzonlte MS*. Metasediraents LR-. Lonely Ridge Granodicr

Figure 41• Geologic map of Lonely Ridge, Rilsen Flateau (after McLelland). SCI 136 intrusive relationships among the several granitic rocks of the batholith. Only four of the seven samples fit an isochron within exper­ imental error. The isochron formed by these four points, 477, 478, 479, . an qg and 480, indicates an age of 611 - 17 m.y. with an initial Sr /Sr ratio of 0.7116 - 0.0003. Two of the samples (482, 483) which do not fit this isochron are greatly enriched in Rb and radiogenic Sr 87 . These samples, and perhaps to a lesser degree sample 481, have not remained closed systems to Rb and Sr and are not suitable, for dating. By assuming n initial Q«7 q c Sr /Sr ratio of 0.704, model ages were calculated for these three samples. The model age for the least affected sample, 481, is 789 m.y. and is a maximum estimate of the age of this rock. The model ages for 482 and 483 are 461 m.y. and 394 m.y. respectively. These two rocks would be expected to indicate a Precambrian model age similar to that for 481, but their degree of alteration in Rb and Sr content makes inter­ pretation of their anomalously young model ages a matter of conjecture. The Late Precambrian-Early Cambrian age of 611 m.y. cal­ culated for the Lonely Ridge Granodiorite is consistent with its intrusive relationship into the metasedimentary rocks, for which an age of 728 m.y. was calculated. An age of 611 m.y. for the Lonely Ridge Gran­ odiorite is not compatible with the model age of 846 m.y. for biotite from one sample of this rock reported by McLelland (unpublished manu­ script) . The biotite sample is numbered 502 and is also plotted in

Figure JL;0. Because the best age consistent with the isochron data is 611 m .y., the model age based on the biotite sample must be in error. 157 87 86 The cause of this anomalous result is probably the initial Sr /Sr ratio of 0.712 which was assumed in order to calculate the model age. It is possible that sample 502/ like 482 and 483, is greatly enriched in 87 radiogenic Sr . The biotite therefore may have had a much higher R7 Rfi initial Sr /Sr ratio than 0.712. A hypothetical isochron for separated minerals from sample 502 would presumably indicate a post-611 m.y. event when that sample was re-homogenized with regard to Rb and Sr.

South Quartz Monzonite Six samples of the South Quartz Monzonite were selected for isochron analysis. The data for these rocks are listed in Table 29 and plotted in an isochron diagram in Figure 42. Samples 506 and 511 are from the southwest wall of Cottonwood Canyon. Samples 507, 508, and 509 are from Windy Ridge. Sample 513 is from an outcrop about half way to South Ridge. Five points fit an isochron within experimental error. This isochron indicates an age of 452 - 14 m.y. for the South Quartz Mon-

87 8fi 4* -5 zonite. The initial Sr /Sr ratio is 0.7248 - 0.0037. Sample 508 does not fit this isochron and a model age has been calculated for this 07 pc rock by assuming an initial Sr /Sr ratio of 0.704. This calculation results in a date of 405 m.y. Sample 508, like sample 482 and 483 of the Lonely Ridge Granodiorite, appears to be enriched in Rb and depleted in normal Sr and does not lie on an isochron. These rock samples evidently have not remained closed to Rb and Sr since intrusion of their respective p lu to n s. 138

Table 29: Analytical Data for the South Leuco Quartz Monzonite/ Nilsen Plateau, Queen Maud Mountains, Antarctica

• Sample Rb Sr Rb87/S r86 (Sr87/Sr86)b ± 2 (ppm) O (ppm)a t error

506 306.1 24.8 34.37 - .54 0.9483 - .0042

507 318.3 18.5 49.59 - ;76 1.042 - .004 508 370.3 8.3 134.7 - 2.9 1.404 1.494 avg. 1.464 - .090

509 117.0 95.9 3.346 - .052 0.7397 - .0041 511 238.9 82.2 7.931 - .123 0.7760 - .0015

513 306.0 20.4 41.64 - .68 0.9737 - .0041

aBy x-ray fluorescence. i> 86 88 Fractionation corrected assuming Sr /Sr = 0.1194 i.5oo 508 O

1.300

1 . POO

Sr' 1.100

/C 1 .0 0 0 T - 4 5 2 ± ll| ra.y.

0.900 (Sr87/Sr86)0 = 0.72i;S *0.0037

0 .9 0 0

0.7C0

figure 42. Isochron diagram for the South Quartz Monzonite, Mlsen Plateau. 140 Summary

Table 30 summarizes the age determinations for the Nilsen Plateau. The metasedimentary, rocks which are the stratigraphically oldest rocks in the Nilsen Plateau, have produced the oldest isochron age, 728 m.y. This age represents the time when these rocks were last metamorphosed and became isotopically. homogenized and closed systems to Rb and Sr. The calculated age of 728 m.y. is a minimum estimate of the time of deposition of the sediments. It may reflect a partial reset­ ting of the metasediments due to intrusion by the lonely Ridge Grano­ diorite . The isochron age of the Lonely Ridge Granodiorite is 611 m.y. This age is a revision of the 846 m.y. model date for this pluton reported by McLelland (unpublished manuscript). The intrusion of the Lonely Ridge Granodiorite and the isotopic homogenization of the m etasediments of the Nilsen Plateau appear to represent the Beardmore Orogeny (680— 621 m .y .) in this area. The metavolcanics which overlie the metasedimentary nocks are probably e quivalent to the Late Precambrian Wyatt Formation of the Scott Glacier area and are probably older than the isochron date of

486 m.y. This date is regarded as a reset date and, together with two samples of metasediments dated at 485 m .y., may reflect intrusion by the younger plutons of the basement complex. One of these plutons, the South Quartz Monzonite, was found to have an age of 452 m.y. and may have been emplaced during the Ross Orogeny. 141

Table 30: Summary of Age Determinations for the Nilsen Plateau, Queen Maud Mountains , Antarctica

Rock Unit Age (m.y.) (Sr87/S r86} + - error t tf °

South Quartz Monzonite 452 - 14 0.7248 - 0.0037 Lonely Ridge Granodiorite 611 - 17 0.7116 - 0.0003

Metavolcanic rocks 486 - 10 0.7150 - 0.0007 Metasedimentary Rocks 728 - 27 0.7117 - 0.0005 142

CHAPTER VI

COATS LAND

Introduction

The Littlewood and Bertrab nunataks are located at 77°53' S. and 34°10'W., about 20 km inland from Duke Ernst Bay in Coats Land, as shown in Figure 43. The Littlewood Nunataks consist of four small outcrops (each is about 50 m in width) at the intersection of the Schweitzer and Lerchenfeld Glaciers. Bertrab Nunatak is located about 10 km southwest, at the intersection of the Lerchenfeld and Penck G laciers. An Argentine party visited Bertrab Nunatak in January, 1955

(Capurro, 1955). In January, 1956, another Argentine group visited the area, but it is not clear whether they went to Bertrab Nunatak or to the Moltke Nunataks, near the shore of the Weddell Sea (Cordini, 1959). J. C. Behrendt (Aughenbaugh and others, 1965) was the first to visit the Littlewood Nunataks when he arrived by helicopter from the U.S.S.

Edisto on January 28, 1959. The geology of the Littlewood Nunataks has been described by Aughenbaugh and others (1965). The rocks exposed in Bertrab Nunatak were described by Capurro (1955), while the Moltke Nunataks may have been visited by Cordini (1959). According to Aughenbaugh and others (1965) the bedrock in all three localities consists of brick-red *

77* 3 0 8

oueen MAUD LAND W e d d e l l Figure 43

N T A4Rft C T I C A

Duke Ernst ■ 11 11 I I I I I I I Boy

, Littlewood N.

I " o , t Moltke f Nunolokt 7 8*00 S

F tLC H N E R

36°W/ 35° W 34* W 143 Figure if.3. Map of Coats Land, showing outcrop areas of the Littlewood Volcanics. 144 acid volcanic rocks which they named the Littlewood Volcanics. On the basis of petrographic descriptions and a partial chemical analysis of specimens from one of the littlewood Nunataks, they classified the rocks as rhyolite or rhyodacite. These small, isolated outcrops in Coats Land are important because they appear to be located at the Weddell Sea end of the trend of the Trans antarctic Mountains. The Theron Mountains, located 150 km southeast of Coats Land, are the nearest major outcrops. Beyond the Theron Mountains is the Shackleton Range, 175 km further south, which in turn lies 350 km away from the Pensacola Mountains. The strati- graphic relationships of the Littlewood Volcanics to the rocks of the Transantarctic Mountains is not known, as no contacts with other rocks are exposed. The nearest exposure of volcanic rock within the Trans­ antarctic Mountains is in the Pensacola Mountains. Radiometric age determinations are virtually the only method of testing the correlation of the Littlewood Volcanics with similar units in the Transantarctic Mountains. Aughenbaugh and others (1965) re­ ported a whole-rock K-Ar date of 840 - 30 million years for a specimen of rhyolite from one of the Littlewood Nunataks. They regarded this date as a minimum estimate of the age of these rocks because of the probability of argon loss from the feldspar. They concluded that the Littlewood Volcanics are of Precambrian age and suggested their tenta­ tive correlation with the older units of the crystalline basement complex of the Transantarctic Mountains. 145 Age Determination

In order to determine a more precise age for the Littlewood Volcanics, seven samples were obtained and analyzed by the Rb-Sr whole-rock isochron method; the data are listed in Table 31 and plotted in Figure 44. Samples 235 and 367 are from one of the Littlewood Nun­ ataks. The remaining five samples are from Bertrab Nunatak, Pre­ liminary reports of the results of this investigation have been published by Eastin and'others (1969) and Eastin (1970). The five rock specimens from the Bertrab Nunatak form a satisfactory isochron which indicates a date of 998.8 - 19.0 m.y. The initial Sr^/Sr®® ratio is 0,7042 - 0.0014. The data for the two rock specimens from the Littlewood Nunataks are compatible with dates

07 OC ranging from 98.5 to 103.3 m .y., relative to an assumed initial Sr /Sr ratio of 0.7042. A pooled isochron of all the specimens from the Bertrab

-f- and Littlewood Nunataks gives a combined age of 1001.1 - 15.8 for these rocks. The initial Sr R /Sr7 f l f i ratio for the pooled samples is 0.7042 - 4*

0.0011. These results are consistent with the interpretation that the rocks of the Bertrab and Littlewood Nunataks crystallized within a short interval of time, 1001 - 16 m*y. ago and that they had similar initial S r^/S r^ ratios. This confirms that the K-Ar date (840 - 30 m.y.) reported by Aughenbaugh and others (1965) is indeed an underestimate of the time that had elapsed since these rocks crystallized. A remarkable feature of these volcanic rocks is that they do 40 not appear to have lost radiogenic Ar during the Ross Orogeny , which occurred in Cambro-Ordovician time about 460-500 m.y, ago. The 146 Table 31: Analytical Data for Rhyolites from the littlewood and Bertrab Nunataks Coats Land, Antarctica

Sample Rb Sr Rb87/S r86 Sr87/Sr86)b (ppm) + a (ppm)a - error ± 2< r

Littlewood 235 95.9 48.4 5.733 - 0.072 0.7871 - 0.0025 Littlewood 367 82.2 62.4 3.831 - 0.048 0.7570 - 0.0027 Bertrab 405 98.4 95.8 2.983 - 0.037 0.7429 0.7442 avg 0.7439 - 0.0013

Bertrab 406 82.9 99.9 2.409 - .030 0.7397 - 0.0013 Bertrab 407 240.5 45.1 15.75 - .20 0.9274 ± 0.0019 Bertrab 408 46.8 357.8 0.379 ± .005 0.7083 0.7098 0.7093 - 0.0015 Bertrab 409 94.4 ' 11.2 25.19 - .31 1.0440 1.0500 1.0485 - 0.0060

aBy isotope dilution, L gg Corrected for fractionation, assuming Sr _ 1.0500

1.0000

0.9500

o <0 co 0.9000

N CD (Jj 0.0500

0.8000 235 = 0.7 04 2i 0.0011

0.7500 ° Bertrab Nunatak

o Littlewood Nunataks

0.7000. 22 26

Figure Ijij.. Isochron diagram for the Littlewood Volcanics Coats Land. unexpectedly high value of the K-Ar date suggests that the rocks of the Bertrab and Littlewood Nunataks may not have been subjected to the Ross Orogeny, which caused widespread metamorphism of the pre- Beacon rocks in the nearby Transantarctic Mountains. CHAPTER VII

WESTERN QUEEN MAUD LAND

Int roduction

The coast of Western Queen Maud Land extending from 2° E. longitude to 6° W. longitude is known as the Princess Martha Coast. The area inland from this coast (71°-74° S. latitude) was investigated by the Norwegian-British-Swedish Antarctic Expedition in 1949-52 (Roots, 1953, 1969). More recently, the geology has been studied by the Soviet Antarctic Expedition, 1961-63 (Klimov and others, 1964), and by the South African Antarctic Expeditions, 1960-present (Neethling, 1964, 1969, Allsopp and Neethling, 1970). The geography of Western Queen Maud Land is shown in Figure 45. Two large outlet glaciers, the Schytt and Jutulstraumen

Glaciers, flow from the polar plateau through breaks in the Kirwan Es­ carpment and the Sverdrup and Gjelsvik Mountains. Between the two glaciers are numerous nunataks and isolated mountains that make up the Borg Massif and Ahlmann Ridge (Ahlmannrygg). The eastern edge of this outcrop area, bordering the Jutulstraumen Glacier near its mouth, is named the Trollkjell Ridge (Trollkjellrygg). The rocks exposed in nunataks on Trollkjell Ridge are mafic to intermediate lava flows with minor tuff beds. Most of the lava is amygdaloidal; quartz amygdules are the most common. The flows show

149 150

------7 V

r i v a fi w v j/ /■: /. r n i! i: <■ 1 h i t d TnlHJilM irt h filftinJ'**'*1

Nunata* I

M*A Rn T H A # COAST ►C ',* Q P R I « C E S V Viittiltfit1rtl? NwMlal u V m ^ v C l."t« A H L w A K N y ™ > v

IUW« N | i | GIAEVS" * * V ij n .i* J ri* « iu r H*U** V‘ """I * HI it**y«'*t*,*r Nw"r#*i < I O G E V i^*klM j ______i : ™ : . ! ______;+kt»U*■~rx - -P* ------■—•—- - - r —■ ■* •-.*; ------_ s ^ r — myf-y ir

luH 11V I e f*|i|l«4M(4 't ', i 'v* • l » PatHC* #■ „ . t t B f 5> *i*** ►*♦** trti iI.k* , ,1 4*iCY»^*i» SVWDEUB '■"'■«• , a. H | M l .* Ghyni.p«>*.*iis- tevL, *y;jsa'f.£ ri fn' , - h . n ft Pm » A ■«-* V H tlM olA t. rrr-j* * - ■ '« fN »«)>«• Ml V'r “ ’ t f f w R l ® ^ KHaJV J S f iJfiti 1 MOUNTAINS MOUNTAINS k Mtn.lM) r4l9j#ta* 5 |1W “ ■ - w - ™ " *o V 0M ,7“ J-tpM H7l [mountains Maw***

r ' > '•*1* 1 ' //. >%V>* I _ w S*J*(jlSfcl v ^ V * JrriiaJV W ,0 ^ r u . . '•-Sip*;«« j|5w)i» »2

MASSif

R 1 T 9 CHJ_? V n t ^ t * *•<(• I 1® «pdA i*a f r»* **t

T f O U f l h p

VI H NM

U P i t * H °

M| » K l P tt Hm UMM r 5<«t* 1 ;1 ,009,000

mtm* 'y«*i S r^ n w

Figure 4£* &aP °* v estern Q,uoen Ma.ud Land (from Roots, 196 ?). 1 5 1 pillow structure and ripple marks are present in the tuffs. The field re­ lationships of the volcanics of the Trollkjellrygg Group were perhaps best summarized by Roots (1969), who noted that they were not in con­ tact with any other formation and were of unknown age. The objective of this part of the study then, is to date the Trollkjellrygg Group and attempt to resolve the problem of stratigraphic succession. Samples of the volcanic rocks were provided by Neethling.

General Geology

The geology of this portion of Western Queen Maud Land is shown in Figure 45, and the stratigraphy is listed in Table 32 (Roots, 1969). The Sverdrupfjell Group are the oldest rocks in the area and make up most of the Kirwan Escarpment and the Sverdrup Mountains. This group consists of quartz-feldspar-biotite-amphibolite gneiss, quartzite, amphibolite, pematite, and gneissic granitic rocks. The known thick­ ness is at least 2000 m. The Sverdrupfjell Group is overlain with angular unconformity

by clastic sediments of the Ahlmannrygg Group. According to Roots (1969), the Ahlmannrygg Group includes all the sedimentary rocks ex­ posed in the Borg Massif and on Ahlmann Ridge (at least 1600 m) ex­ cepting the Trollkjellrygg Volcanics. The stratigraphy of Ahlmann Ridge itself has been reported by Neethling (1969) and is shown in Table 33. In addition to the Ahlmannrygg Group, Neethling has defined two younger clastic sedimentary units, the Tindeklypa and Istind Formations, which unconformably overlie the older rocks. 152

Table 32: Stratigraphy of Western Queen Maud Land, Antarctica (from Roots, 1969)

Stratified Rocks Intrusives

P'eridotite Miscellaneous: gabbro, d io rite, syenite Borg Intrusions Trollkjell Group c ■g Ahlmannrygg Undiff, elastics •S 0 Raudberg Fm. (0 *3 Group: Upper Borg Fm. « g Lower Borg Fm. £ © Fram Fm. I-. (D a) a Pencksokk Formation b i J Tvore Intrusions Heksegryte Intrus,

Juletopper Intrus. pC? Sverdrupfjell Group 153 Table 33: Stratigraphy of Ahlmann Ridge, Western Queen Maud Land, Antarctica (Neethling, 1969)

Dolerite sills Jurassic (?) or younger Dolerite or basic dike Peridotite dike Jorgen Syeno-Diorlte

Pre cambrlan Roberts Knoll Peridotite (?), possibly younger Boreas Dolerite Borg M etamafics Trollkjellrygg Group Precambrian Istind Formation (?), possibly Paleozoic Tindeklypa Formation unconformity Jutul Volcanics Nils red beds Ahlmannryggen Grunehogna arenite Formation Precambrian Schumacher sediments (?) unconformity?

Pyramiden beds 154 The Ahlmannrygg Group has been extensively intruded by sills of feldspathic, diabiasic gabbro of the Borg Intrusions. These sills, as well as the Ahlmannrygg Group, have undergone low-grade regional metamor­ phism. McDougall (in press) reports a K-Ar date of 1650 m.y. on horn­ blende from the Borg Intrusions. He also reports a K-Ar date of 825 m.y, on plagioclase from a dolerite at Boreas Nunatak, which may be part of the Borg Intrusions. The 165 0 m.y. date was substantiated by Allsopp and Neethling (1970), who reported a Rb-Sr whole rock isochron + age of 1700 - 130 m.y. for the Borg Intrusions. The Ahlmannrygg Group must therefore be older than 1700 m.y. According to Neethling (1969), two intrusions younger than

the Borg Intrusions occur on Ahlmann Ridge; these are the Roberts Knoll Peridotites and the Jorgen syeno-diorite. Allsopp and Neethling (1970) reported a Rb-Sr whole rock isochron date of 1030 - 70 m.y. for the Jorgen intrusive. The age of the Roberts Knoll body is not known. The relationship of the Trollkjellrygg Group to the other rocks of Ahlmann Ridge is not known. The Trollkjellrygg andesite and basalt flows and tuffs are not in contact with any other unit. Klimov and others (1964) supposed that they were correlative with the Jutul volcanics which are contemporaneous with the Ahlmannrygg sediments. The table of Roots (1969) (Table 32) and that of Neethling (1969) (Table 33) both place the Trollkjellrygg Group above the Ahlmannrygg Group. Neethling implied that the Trollkjellrygg Group is older than the Borg and Jorgen Intrusives by placing the volcanics beneath the intrusives in his strati- graphic table. He also indicated the Trollkjellrygg volcanics to be younger than the Ahlmannrygg Group and unrelated to the Jutul Volcanics. 155 Neethling (written communication) has recently revised this sequence, however, to agree with the Russian interpretation, combining the Ahlmannrygg Group and the Trollkjellrygg Group into the Ritscher Super­ group .

Age Determinations

Nine samples of the Trollkjellrygg Group were analyzed for

an age determination. The data are listed in Table 34 and plotted in Figure 46. Eight of the samples fit an isochron that indicates a date of 856 - 30 m.y. with an initial Sr^/Sr®*’ ratio of 0.7097 - 0.0009. One sample, 484, which is from the lowest member of the volcanic sequence, does not fit this isochron. If an intercept of 0.7097 is assumed, a model age of 1735 m.y. can be calculated. However it is equally possible that this specimen was contaminated with radiogenic 87 87 86 Sr at the time of extrusion and that its initial Sr /Sr ratio, there­ fore, may be higher than that of the other samples. Two other possi­ bilities are (1) 484 has not remained a closed system for Rb and Sr, and (2) 484 may have a different age than the other samples. However, the map of the Trollkjell Ridge area (Figure 45) does not show any near­ by intrusions that could cause partial or complete rehomogenization of Rb and Sr in the Trollkjellrygg Group. Sample 484 does not show any lithologic differences from the other eight samples. Its position as the only sample from the lowest member of the volcanic sequence appears to be its only characteristic field relationship. 156 Table 34: Analytical Data for Volcanics of the Trollkjellrygg Group, Western Queen Maud Land, Antarctica

Sample Rb Sr Rb87/S r86 {Sr87/S r86)b (ppm)a (ppm)a - error - 2

484 37.3 115.7 0.7577 - .0122 0.7282 - .0038 485 120.1 179.6 1.543 i .023 0.7284 - .0030 486 158.3 134.7 2.714 - .042 0.7446 - .0028 487 129.3 57.6 5.183 - .081 0.7725 - .0020 488 96.5 151.7 1.486 - .023 0.7281 - .0016 489 118.7 110.7 2.469 - .039 0.7374 - .0018 490 102.2 146.0 1.606 - .026 0.7285 - .0008 491 46.2 141.2 0.7399 - .0135 0.7210 - .0026

492 51.3 142.5 0.8454 -.0130 0.7205 - .0030

aBy x-ray fluorescence. b 86 88 Fractionation corrected assuming Sr /Sr = 0.1194. 0.780

Sr

T - 5£6 i 30 m.y. 0.720 (SrQ7/£r86)0 = 0.7097 ±0.0009

0.700

Figure lj.6. Isochron diagram for the Trollkjellrygg Volconlcs, western Queen Maud Lond. 157 Summary

The age of the Trollkjellrygg volcanics is 856 - 30 m.y.

Therefore, the stratigraphic sequences suggested by Neethling and Roots should be revised to show the Trollkjellrygg Group as younger than the Jorgen syeno-diorite. There should also be an unconformity at the base of the Trollkjellrygg Group. The coincidence of the model age of the basal sample of the Trollkjellrygg Group with the age of the Borg Intru- 87 sions may be due to contamination with radiogenic Sr Inspection of the radiometric dates listed in Table 35 seems to indicate two periods of igneous activity in Western Queen Maud Land: (1) The intrusion of the Borg diabase sills at 1700 - 130 m.y. (2) The intrusion of the Jorgen syeno-diorite and the extrusion of the Trolkjellrygg volcanics at 1030 - 70 m.y. and 856 - 30 m .y., respectively. The K-Ar mineral dates of 825 and 1010 m.y. reported by McDougall (in press) probably reflect the re-heating of Borg Intrusions by this late activity. 159

Table 35: Radiometric Dates from Western Queen Maud Land, Antarctica

Rock Unit Age Reference and Method

Trollkjellrygg 856 - 30 m.y. This study; Volcanics Rb-Sr rock isochron. Borg Intrusions 825 McDougall, in press; (?), Boreas K-Ar, p lag io clase. Nunatak

II tl 1010 McDougall, in press; K-Ar, pyroxene. Jorgen 1030 - 70 Allsopp & Neethling, syeno-diorite 1970; Rb-Sr rock isochron. Borg Intrusions 1650 McDougall, in press; K-Ar, hornblende. II II 1700 - 130 Allsopp & Neethling, 1970; Rb-Sr rock isochron. CHAPTER VIII

CONCLUSIONS

The ages that have been determined for the rock units anal­ yzed in this study are listed in T3ble 36 and arranged in a correlation chart in Table 37. The earliest event detected is the crystallization of the felsic flows interbedded with the sediments of the Patuxent Forma­ tion in the Neptune Range of the Pensacola Mountains. The age of these flows and the time of deposition of the Patuxent Formation is 1210 - 76 m.y. The Patuxent Formation is therefore one of the oldest rocks in the Trans antarctic Mountains. The presence of rocks older than 1000 m.y. in the Trans- antarctic Mountains has only recently been reported. Grindley and McDougall (1969) reported an average date of 1020 m.y. by the K-Ar method on hornblende from amphibolite and pegmatite of the Nimrod Group at the head of Nimrod Glacier. They interpreted these dates as marking the end of regional metamorphism during the Nimrod Orogeny which they postulated may have produced the several occurrences of high-grade metamorphic rocks that have been reported in the Shackleton Range (Stephenson, 1966), the Wisconsin Range (Murtaugh, 1969), and Victoria Land. The age of the Nimrod Group was determined by Gunner and Faure (1970), who reported a Rb-Sr whole-rock isochron age of 1980 m.y. for these rocks. They may be even older.

160 161

Table 36: Summary List of Age Determinations

Location Rock Unit Age (m .y.)

Pensacola Gambacorta Formation 568 - 39 M ountains Serpan Granite and Gneiss 555 - 26 D iabase 778 - 59 Felsic flows 488 - 6 (a)

II t l 1210 - 76

Patuxent Formation 402 - 5 (a) Thiel Mountains Biotite Granite 350 - 20 Quartz monzonite porphyry 409 - 4 Cordierite-hypersthene quartz monzonite porphyry 632 - 102 Nilsen Plateau South Quartz Monzonite 452 - 14 Lonely Ridge Granodiorite 611 - 17 Metavolcanics 486 - 10(a) Metasediments 728 - 27 (a?)

Coats Land Littlewood Volcanics 1001 - 16 Western Queen Maud Land Trollkjellrygg Volcanics 856 - 30

a Re se t date Table 37j Correlation Chart of Bailment Rook Units Dated Proa The Central Tranasntarotle Hountalns

G eological Ago V ostern Queen . Pensacola T h iel H o rlle t Ellssn Plateau Orogeny Coat* Land Rlnrod Glacier Period K, Y n , Kaud Land Mountains Kountoln* Mountain* Scott Glacier A roe C*rbon- _lfarau* Baaeon Baaeon Beacon 350 B io tite G ranite Savonian Beacon (1) Group Group Group 6oa 602 Patuxent Ft. 609 Qta-Kon Porph. _JSllurian, re e o t 652 South Qtz-Kon. 658 Klnrod Group Crdo- i Roia 672 Rhyollto r e s e tj TlClan I 60S Patuxent Fit, 679 Qtr-Iton. b 686 Katsvoleantea flows reset 699 KhyolJta re s e t 500 555 Serpan Granite and Gneiai Casbrlan1 568 Oanbaeorta Fa, Uelaon La. Leverett Frt. Leverett Fh. Shackleton Li. 600 632 C-H-Q Konxonlte 627 Crenodlorlteb 611 Lor.ely Ridge 600 iilnrod Group Be enino re t Porphyry 633 V yatt Ftx. Granodiorite r e s e t. 1 re * e te Katavoloanloa i 700

Pre- Kstasedlnenta La Gore* Fb . 723 Keteaodinent* 778 Patuxent Fa, dlabaee till* 800 caab rlan :B56 Trollltjoll- i rygg sole. i I'i-V 1000 I Slarod '1030 Jorgen InJlOOl L ittle- 1020 lilnrod Group tru s io n . wood Vola (E-Ar born.) 1210 Patuxent Fa. f flow* dsp.

1700 Veatfold 1700 Borg Intn (first) . eior.9a j

1980 Hlnrod Group, 2000 Ahlnannrygg Group

a. Allsopp and Keethllng, 1970. b. Faure and others, 1968. d. Gunner and Faure, 0. Monttgny and Faure, 1969. In press. i_j e. Crlr.dley and Mo -tt, D ougsll, 1569. {(j 163 Because of the great age of the Nimrod Group, they can no longer be regarded as being contemporaneous with the Patuxent Forma­ tion. Roots (1969) had suggested a correlation of the Patuxent Forma­

tion with the Ahlmannrygg Group in Western Queen Maud Land, How­ ever, Allsopp and Neethling (1970) reported an age of 1700 m.y. for the Borg Intrusives which cut the Ahlmannrygg Group, The sediments of the Ahlmannrygg Group are therefore older than 1700 m.y. and older than the Patuxent Formation. The Patuxent Formation may, however, coincide with a period of sedimentation represented by the Turnpike metamorphics in the Shackle- ton Range (Stephenson, 1966), metasediments in the Thiel Mountains (Ford, 1964), and the LaGorce, Duncan, Goldie, and Cobham Formations of the Horlick and Queen Maud Mountains (Mirsky, 1969, and Grindley

and McDougall, 1969). The metasediments of the Nilsen Plateau, probable equivalents of the LaGorce Formation, were found to have an age of 728 - 27 m.y. This is the first age determination of these rocks which is in agreement with their stratigraphic position. Even so, the indicated age represents the time when the rocks were isotopically homogenized and closed to Rb and Sr. Deposition of the sediments probably took place earlier. The next event determined by this study is the extrusion of •J* the Iittlewood Volcanics in Coats Land at 1001 - 16 m.y. This event, together with an age of 1030 m .y. reported by Allsopp and Neethling (19/0) for the Jorgen syeno-diorite of Western Queen Maud Land and the 1020 m.y. date on hornblende from the Nimrod Group (Grindley and McDougall, 1969), appear to indicate the widespread nature of the 164

Nimrod Orogeny. Angino and Turner (1964) termed a related event on the East Antarctic Shield the Bunger Orogeny. In Western Queen Maud Land, + the crystallization of the Trollkjellrygg Volcanics at 856 - 30 m.y. and a date of 825 m.y. by the K-Ar method on plagioclase from the Borg Intrusives (McDougall, in press) may indicate a later phase of the Bunger Orogeny. It is not clear whether the Nimrod Orogeny affected the Pen­ sacola Mountains. Although the best estimate of the age of the diabase sills intruding the Patuxent Formation is 778 - 59 m .y., the sills may be as old as 1267 m.y. In either case, because the sills are folded along with the intruded sediments, it is not possible to pinpoint the time of folding as part of the Nimrod (~ 1000 m.y.) or the Beardmore {•^ 625 m.y.) Orogenies. The limiting dates of folding of the Patuxent Formation are 1210 m.y. (the felsic flows) and about 550 m.y. (the Middle Cambrian Nelson Limestone). In the Nilsen Plateau an undetermined interval of time sep­ arates the metasediments and the discordantly overlying metavolcanics. The Wyatt Formation, probably correlative to the metavolcanics of the Nilsen Plateau, was found to have an age of 633 m.y. in the Wisconsin Range by Montigny and Faure (1969). If the 728 m.y. age of the meta­ sediments and the 633 m.y. age of the Wyatt Formation are not reset dates, they may indicate the actual interval of time between deposition of the two units. However, there is evidence of the Beardmore Orogeny (620 - 680 m.y.) in both the Nilsen Plateau and the Wisconsin Range. The age of the Lonely Ridge Granodiorite of the Nilsen Plateau is 611- 17 m.y. 165 This corresponds to the age reported by Faure and others (1968) of 627 -

22 m.y. for a granodiorite pluton intruding the metamorphic rocks of the

Wisconsin Range. The cordierite-hypersthene quartz-monzonite porphyry of the Thiel Mountains was found to have an age of 632 - 102 m.y. It also intrudes metasedimentary rocks. These plutons may have produced reset radiometric dates on the metamorphosed sedimentary and volcanic rocks that were intruded. No events during this period were detected in the Pensacola Mountains, but the isoclinal folding and low-grade meta- morphism of the Patuxent Formation may have occurred at this time (Schmidt and others, 1965). Gunner and Faure (1970) recorded a date of about 600 m.y. from metasedimentary rocks of the Nimrod Group at the head of Nimrod Glacier, indicating a metamorphic event at the time of the Beardmore Orogeny. Their Rb-Sr analyses did not, however, detect the Nimrod Orogenic period reported by Grindley and McDougall (1969) from K-Ar analyses on hornblende. Following the Beardmore Orogeny, a period of erosion lowered the land surface. A marine transgression then resulted in deposition of a widespread limestone unit containing Middle Cambrian fossils. This is the Nelson Limestone in the Pensacola Mountains (Schmidt and others, 1965), part of the Leverett Formation in the Scott Glacier area (Mirsky, 1969), and the Shackleton Limestone of the western Queen Maud Mountains (McGregor and Wade, 1969). The next event is the Ross Orogeny, a period of thermal meta­ morphism, granitic intrusion (the Granite Harbour Intrusives) and volcanism, in Cambro-Ordovician time. The Ross Orogeny in the 166 Pensacola Mountains is recorded by the intrusion of the Serpan Granite + and Gneiss at 555 - 26 m .y., and volcanic activity represented by the •j* Gambacorta Formation whose age is 568 - 39 m.y. Most of the felsic flows of the Patuxent Formation were isotopically rehomogenized at this time and record a reset date of 488 - 6 m.y. The thermal effects of the Ross Orogeny in the Patuxent Range of the Pensacola Mountains did not subside until the end of the Silurian; the reset date of 402 m.y. for the Patuxent Formation indicates this cooling period. The Thiel Mountains apparently were also active at this time. The age of 409 m.y. for the quartz-monzonite porphyry that intrudes the cordierite-hypersthene quartz-monzonite porphyry coincides with the Ross Orogeny. Model ages calculated for the biotite granite indicate that it is about 350 m.y. old and probably contemporaneous with the quartz-monzonite porphyry. Several granitic plutons were intruded into the rocks of the Nilsen Plateau during the Ross Orogeny. The South Quartz Monzonite + is found to have an age of 452 - 14 m.y. During this time the Lonely Ridge Granodiorite was severely deformed cataclastically and the meta- volcanic rocks were reset isotopically to a date of 486 - 10 m.y. The same orogenic period was recorded in the Wisconsin Range by crystallization of a quartz-monzonite pluton at 479 - 10 m.y. and by rhyolites dated at 498 - 454* m.y. and 472 - 11 4* m.y. (Faure and others, 1968). Metasedimentary rocks in the Wisconsin Range were found to have a reset date of 460 - 16 m.y. by Montigny and Faure (1969). Gunner and Faure (1970) likewise found that an internal isochron on mineral separates from the Nimrod Group showed isotopic rehomog- 167 enlzation at 456 t 14 m.y. Orogenic activity in the Wisconsin Range

and the Queen Maud Mountains appears to have ceased about 50 m.y. sooner than in the Patuxent Range and the Thiel Mountains. The cooling and period of erosion following the Ross Orogeny completes the known sequence of events in the formation of the base­ ment complex of the Trans antarctic Mountains. Lack of evidence of any post-Nimrod (or post-Bunger) orogenic activity in Coats Land suggested that, like Western Queen Maud Land, it is a part of the East Antarctic Shield and has not undergone the same history as the Trans antarctic

M ountains. APPENDIXES

1 6 8 Appendix Ai Computer Programs 1. Isochron analysis Z, Sr isotope ratio analysis 3. Rb/Sr ratio by XRF 4. Rb and Sr concentration by XRP Standard deviation

Appendix B: Sample Descriptions APPENDIX A: COMPUTER PROGRAMS

Rb—Sr Isochron by York's Method (1966)

Fortran IV G Level 18

Input data: L - No. of data sets to process

Title of isochron B = Estimated slope N = No. of points to be fitted

SPEC1,2 = sample no. X (I) = X value R (I) = of X value

Y (I) = Y value S (I) = ti^of Y value C RB-Vr ISCCHRCN BY YCRK'S BEST FIT. ’ VER~OF"5-20-7C Q______X. (RB87/SR86) AT Y f_JSRe?/5R8fi )CCRR. ______1 7 1 C KECu'lKES EST. SLCPEtB), NC. CF POINTSIN), t WEIGHTS CKX C V. C. _ IMPLICIT REAL*8 tA-H,C-Z) ______REAL*4 SFEC1, 5PEC2 DIPENSICN X (200 ) • Y 1200 ) » U(2CC), V(2CC), P(2C 0), C12C0), WI2C0), ______15CW (200J L RE5X(200) , RE_SY (2Q0Jj_SP.EC 1 (ICC). SPEC2UC0), R(2CC). S( 12C0) ■J READ (5.11) L ______11 FCRPAT (13) ______DC ICO J * l, L „ ______READ (5,12) 12 fcrpat (ihOjlLFatej_s_ap.ple_ncsLCCATJGNj_EIC. ______1 * • ) ■_____ WRITE (6,12). READ (5,1) B, N, I SPEC 1(1 ), SPEC2( I ) »• X 11 ), R (I), Y (l>, S ( I ) , 1 = 1, IN) _ „ ______“l FORPAT (F15.8,ii0'/(2A^,2X,F15.e,F15.iC,Fl5.8,Fi5.1C) ) WRITE (6 ,3 4 ) B, N 34 FCRPAT ( IHO,’ ESTIMATED SLGPE = * ,F 15 .8 ,* NO. OF SAMPLES = • , 110) 2C0 CCNTINUE „______.______SUPK=0 SUPA = 0______SUPB = 0 SUPC = 0______SUPC = 0 supe_=_o ______:______SUMS = 0 SUPJ =_0______XBAR = 0 YBAR = 0______DC 2 I = 1, N p ( I ) = i .q/.(Rj I )**2) C(I ) = 1.0/(S(I)**2) HU )__= P (I )*C (I )/ID *E»C (IL± PJJJ ) SCR1I) = WU)**2 _2_SUPW = SLPW » _H.( IJ______CC3I ~ 1, N —XBAR S-XBAR. + H ( I ) *X (1 ) /SUPW. 3 YBAR = Y t AR ♦ H(I)*Ytl)/SUPW AC_$_I. = _1, , N ______U(I) = XU) - XBAR y.UJ_=_Y.( I » _=:,YBAR ____ SLPA = SLPA ♦ SCW((J*(U(I)**2)/P(I) _slpb_e_slpb t_scwm*u(i)*vu)/p(i) SUPC = SLPC ♦ SCW(I)*(V(I)**2)/P(I) SUPO = SLPC ♦ H(I )»(U( I)»»2)______4 SUPE = SLPE + W(I )*U( I )*V( I ) CCA = 0.£66fc667*Sl)PB/SUPA______COB = (SLPC - SUPC)/(3.C*SUPA) j — CCC = -SLPE/SUPA , CPHI = (CCA**3 - l.5*CCA*CCB + 0.5*COC)/(CCA**2 - CCB)**1.5 . (F(CPH(*<2 - t.0 1 6,6,1C ______6 ALPHA = (CSCRT(1 .0 - CPF 1**2 ) )/CPFI IF(^ALPf-.A) 7 ,7 , B 7 PHI = OA1 AN(ALPHA) CC _TC 9 . ______8 Phi = 3.1415927 + CAT AM ALPHA ) 9 SLOPEA = CCA + 2 . 0*CSCRTI CCA**2-CCB)*CCCS(P F I /3 .0 ) j SLCPEB = CCA + 2.0*CSCRTICCA**2-CCB)*CCCS((PHI+6.2B31S5)/3.C) SLOPEC = CCA_i 2.0*CSCRT(CCA**2-CCB)*CCCS((PH 1+12 .5 663 7) /3 . C ) ______j GC TC 30 10 A = 3.0* (CCE - C0A**2) ... _ _ C = - 2 . 0 * (CCA**3) * 3 . C*CCA*CCE - CCC Z = t-C/2.0 ♦ DSCRTUC**2)/4.C + tA**3)/27.C))* *(1.C/3.C) Vlll = (-C/2.0 - CSCRT((C**2)/4.0 * (A**3)/27.C))**(!.C/3.C) .SLCPEA = 2 ♦ V(.U +..CCA______.______SLCPEB = O.CCCOCOOO _ SLOPEC = O.CCCOCOOO .___ ;______T/fe 3C TEST1 = CABS(B-SLCPEC) ^ TEST2 = CABS(6*0.01) ______1 1F(TESTI.LE.TEST2) GG TC 38 B = SLCPHC______GC TO 2CC 30 A I M = Y B A R SLOPEA*XBAR ______:______BINT s YEAR - SLCPEB#XBAR ____ CI NT * YEAR - SLOPEC#XBAR ______SUPRX = C.O _____ SI^FRY _=„C.O______DC 31 I = 1. N ____ 5UFS...r-.SlFS„4 Will* (SLCPEC*U( t) . V( I) )**2______s u n = SLPT + M 11) * ( X I 11**2) ____ R E S X n ) = ,-(SLOPEC )#W( I )*ICINT4SLCP£C#X( 11-YIII )/ ( P ( U * X U ) J______RESY(I) = W (I)*(CINT4SLCPEC*X(I )-Y ( 1 ) ) / (C II )* Y I I) ) SUPRX. .=_ .SUPRX *_ RESX (I)______:______l______31 SUPRY = SUPRY + RESYtl) _____ A_N_= N ______SIGFAB = CSCRTlSUPS/t(AN-2-01*SUPC) ) SIGPAA = SIGPAB*D5CRT(SUMT/SUFW)______WRITE (6,32) 32_JiCRiiAT._(. 1 b0.iJ_S AKfiLE R.087/SR_06._ (*/.$_ SIGPA_ ._R.B/.SR WEIGHT R/.S___ 1 RESICUAL SR87/SR86 S/S SIGKA SR/SR HEIGHT S/S RESIDUAL

w rTt e” ( 6 7 3 7 Y - (spec I T i T , s p e c 2 Tf )T x (i ) ,r'( i i, p (f >*7re sx i'ff, v T n , sT i »7c JULL).«RES.Y.(.I) ,..l?„l.f N )______33 FORPAT ( 1H0,2AA,F12.6,F12.6,C15.6,F15.S,F15.6,F12.6,D15.6,F15.8) _____ WRITE 16 ,A3JL SUPRX, SUPRY______:______A3 FCRPAT ('O',33X,'RESICUAL SUP =•,F15.0,20X,•RES IDUAL SUP =',F15.8> _____ WRITE 16,35) XBAR, Y B A R ______'______35 FCRPAT I///* THE CCCRC INATES CF THE CENTROID CF REVOLUTION (YCRK, 11966) _A R J XBAR =JLfFl5.0,^ YBAR = ' , F 15.8 )______WRITE (6,36) SLCPEA, AINT, SLCPEB, BINT 36 FCRPAT (1H0,* THE FIRST TWC RGCTS CF CUBIC ECUAT1CN ARE SLCPEA ^ ___ 1F15.8,' '* A INT =',F15.8/A5X,'SLCPEB =',F15.8,' BINT =',F15.8 1) . ______HRITE (6,37) SLCPEC, SIGPAB, CINT, SlGPAA ' 37 FCRPAT (IHO,1AX,'THE TH IRC RCCT £ BEST SLOPE = SLOPEC =',F15.8,'_____ I 'ITS STC DEV = SIGPAB = •*, F15.8/IHO,23X, « THE BEST INTERCEPT = CIN 2T =' , F 1 5.8.' ITS STC CEV = SIG H AA =', FJL5_._8J______XYSUP = C ! XSUP f _ _ 0 ______:______; YSUP = 0 ! SUPX2 = C______[ SUPY2 = C DC AO 1 = 1, N ______XYSUP = XYSUP + Xin*YIII x s u p = x s u p ♦ xij) ...______;______SUPX2 = SUFX2 + X (I ) **2 SUHY2, = SUPY2 + Y (I) * *2 ______YSUP = YSUP + Y (i) AC CONTINUE ______ANUFER = j AN#XYSUP) - (XSUF*YSUF) DENCP=(CSCRT((AN#SUPX2)-tXSUP**2)))*(CSCRT((AN*SUPY2>-IYSUP##2) ) )____ CCRCCE = ANUPER/CENCP WRITE (6,A2) CORCCE ______A~2 FCRPAT ( IHO,27X,'CORRELATION COEFFICIENT =',F15.8) AGE *=_(1C00. ♦ CLOG I SLCPEC 4 l.))/0.0139 ______AGEPAX = (1C00. # DLCG(SLCPEC4SIGPAB4l.)J/C.C139 AGEPIN = (ICCO. # CLCG(SLCPEC-5IGPAB4l.))/C.0139 ______AGERCR = ((AGEPAX-AGE)4(AGE-AGEPIN))/2. WRITE (6,A1 ) AGE, AGERCR ______A1 FCRPAT ( IHO»13X , * THE ISCCHRCN AGE IN PILLIONS OF YEARS =',F11.A/1H 10.2AX, 'EPHCR IN FILLICNS CF YEARS = » ,F11.A)______WRITE (6,99) 99 FCRPAT ( 1H 1 )_.______ICC CCNIINUE SERPAN GRANITE ♦ SERPAN GNEISS 20JULY

___ ESHHAJEC. .SLOPE.-__0 .C083CC00 ___ NO. OF !SAKPLES.-...... U _____ ...... — ------, . . , .. — — . ----- .. SAHPLE RB87/SR86 R/S SIGKA RB/SR WEIGHT R/S RESICLAL SR87/SR86 S/S S1GHA SR/SR WEIGHT S/S RESIOUAL 626 C.962318 0.0169C2 0.650309C 06 0.06528116 C.715300 C.CC020C C.25CC00C 08 -G.001617B1

. .625______... 1.36671 ?__ _0.021C60 __0.225667C 06 -C.C0667776 ____ .C.7157CC__ o.ccoecc. . 0.156210C.C7.. 0.00166U6 .926 . .. C.286236 C.C06618 0.512329C 05 -C.C1162655 0.7C7800 C.CCC20C 0.25CCC0C 08 0.00123609 627 C.6096CC C.C06575 0.2313170 05 -C.C0C16376 C.7C87CC O.OC22CC C.2C6612C 06 C.CC136899 ___628 ______1.C19516__ ..0.015786, ... 0.6013B9C 06 . -C.CCCBC826. ___ 0.713C0C o.ocieoc C.3C8662C 06 C.OC196203

629 C.382598 O.C06C57 0.27Z576C 05 -C.CCCC2335 0.709600 0.001600 0.510206C 06 C.CC0Q8695

63C 3.156809 C. 068669 0.626020C 03 0.C0C5C263 C.731 IOC C.0C160C 0.51C2C6C 06 -0.0C023391

...631______l. 156628.__ .O.C18333 __0.297531C 06 C.C0C57789 ..C.7162CC___C.CCl 70C.__C.366C21C. .06 .. -0.OC1O369O 632 11.637306 . 0.196970 0.263066C 02 -0.C07319C6 0.793300 0.0C3C00 O . m i l l C 06 C.00328656 633 11.667766 0.186129 0.296955C 02 -0.01266668 0.7936C0 • C.0C26CC C.167929C 06 C.00679572

uses___ ...16, 76C0C0 C. 176250 0. 3293680 02 -C.C0762926. C.81.5600. O.OC3COO 0 .1 U 1 1 1 C 06 ,C. 00528208 RESIOUAL SUM - 0.C0167I06 RESICUAL SUN - 0.01696892

.THE COORDINATES.CF THE_CENTROIO.CF REVOLUTION (YORK, .19661 ARE XBAR - . _ C .71138563 YBAR .« ____ 0.71200633

THE FIRST ThO ROOTS CF CUBIC EQUATION ARE SLOFEA - O.C225e6S6 AINT - 0.69596C01 SLOPES ■ -0.01515225 BINT - 0.7227E562

THE THIRD ROOT *£ "BEST SLOPE - SLOPEC C.CC773930 ITS STC DEV - SIGNA8 - "* 0.CC036755'

ThE BEST INTERCEPT"-" CINT~i 0.70650071 ITS “STD DEV - SIGhAA* 07CCC66B29 ...... -CORRELATION COEFFICIENT - 0.59970259

THE ISOCHRON AGE IN PILLIONS OF YEARS - *156.6605 ...... ' “

eFroF iTTFill'ions of years' - 2 6 .2 3 9 1 ...... 174 2. Sr Isotope Ratio Calculation Fortran IV G level 18 Input data: ND = No. of data decks (runs) to process Title of run N = No. of sets (of six scans each) in run

RB85 Measured peak heights for isotopes scanned. SR86 Ratio between recorder scales for Sr88 and the SR87 other three isotopes = 10:1 SR88

BASE = Baseline of scale used for Sr88, read between Sr peaks and recorded on alternate scans only Calculated variables: SUM85-88 = Sum of peak heights for six-scan set SUMB3 = Sum of Sr88 baseline for three scans SUMB6 = Sum of Sr88 baseline for six-scan set SUM88C = Sum of Sr88 peaks adjusted to the same scale and baseline as the other peaks S8786 = Ratio of Sr87/Sr86 S8786C = Sr87/Sr86 corrected for fractionation assuming Sr86/Sr88 = 0.1194 A8786 = Average of Sr87/Sr86 Ratios for N sets of run DSQ = Square of difference of S8786C value from average (SR87/Sr87)(-, value HI8786 = Maximum value of Sr87/Sr86 SL0876 = Minimum value of Sr87/SR86 HISRC = Maximum value of (Sr87/Sr86)c SLOSRC = Minimum value of (Sr87/Sr86)^ 175 P,Q,R = Single-dimensioned counterparts of isotope ratios, required by plotting subroutine

P^OTA ) Printer plot subroutine used at The Ohio State PIOTC ) University Computer Center

SRC2 = (Sr87/Sr86)c values which differ from the mean by less than 2 K = Number of these values ASRC2 = Average of these values DSQ2 = Square of the difference of SRC2 values from ASRC2 SDSQ2 = Sum of DSQ2 values STDEV2 = 6 of group of SRC2 values SDMEN2 = l> of group of SRC2 values A87862 = Average of SRC2 values 5 CONTINUE 35 ______------SUMO 0 = SQ — ______------S8 8 11)—=—SUMQ6/SUM38C 3 6 ------5 CONTINUE 25 I ______------: 0.0- = SUK87 — ------RT ( 50) 0 ,5 (6 HRITE ^ ------A » 'ECTE' ^ D -SR.* 'B7/5i-».'Rfl6—L,-*RAIIJLfT-O- , T68 0.0 0 = TB688 i FORMAT-!.13) - 4 ------______15 FORMAT. {F5.1*5X,F4.0,6X,FA.0»6X,FA,Q,AX,F.A.l J ______FORMAT. 15 {F5.1*5X,F4.0,6X,FA.0»6X,FA,Q,AX,F.A.l ------1 SCUU, E(O) IARY 48» HA19, RLI) AL1(6) ; ), ABL 6 ( 1 0RDL1I6), I HEAD1I91, ARRAY! », 1428 SET(IOO), SRC2U0U), 1, : 1 : ______------SUM88, SUP87, SUM86, SUM65, ABL2, 0RDL2, ABL?, CRDLl, SET, REAL*4 ~ ______------______n h n 5 OMT IO 3 7 F 1,F7.1,3F14.6) , 1 . 7 F , .1 0 5F1 , 1 F7. , 0 FORMAT F3. IIHO, 75 0 OMT 0 E R8 S8 S8 S8C R8 S SR88 SR87C SR87 SR86 RB85 SET *0 FORMAT I 50 U .6 SB7U61UV.B6, FRA IH,'U N. DT, APE O + LOCATION + NO. SAMPLE DATE, NO., 'RUN FORMAT I1H1, 5 R STP RTO AC I AD E SA, IK CT AUS RAE TA ! VALUES CUT GREATER THAN PICKS SCAM, CARD PER I CALC. RATIO ISOTOPE SR R8 BASE 1R88C C02(. ) 3 I 2 L B A 2CR0L2 (7.1 DIPENS ION S8786(ICO !, 3 8 6 8 8 4 1 0 0 ], .SB786C(100J , . DSQ11001, . DSQ211001 DSQ11001, . , .SB786C(100J ], 0 0 1 4 8 8 6 8 3 !, DIPENS S8786(ICO ION ,B6 R'' O'' .URED*, S8,'6SR*' ,'AI•,•CORR' , • , R' ATIO• •, 8 *,'8 R 6/S ' SP8•, ,' * D E R '.'U S A E '.'H IO T '.'A R 6 ','B R 3 LJOTEL- !_,J L,J-OAT-E-L,-! 2 ) AR . =. -SR86-*~SLM86- SUK36 1ABRT LSUMB3 SRSiL*—BASE,_SUMG6 SR36,_SRB7-. «—R385-, _SUM87C.». ,_RB8Z,_SUK88(1,

SUMB3-=—0 0 . ------______B7 SM5 0.38600L------; L 0 0 6 8 3 . 0 * SUM85 = RB87 AB68B _=„T868B /N SI) ((S76() 88C. . C00I 2 * 000.I* 1C *. A8786CJ. S8786C(I) ( ( = DSQII) 0 0 =, N 1=1, 40 00 =_.S8786 ( T8786 TS7B6C -a—S8786CI1)—*■—T8786C 83C T0786C/N = A8736C 88 = T87B6/N = A8786 U BC (U8 * U8) 10.0 0 1 * SUM86) * (SUM88 SUMB8C = R T (,5 SFTt) SM5 SM6 SM7 SP7, U8, U8C S SUM88C, SUM88, SUP87C, SUM87, SUM86, SUM85, tI), T F S (6,75) WRITE UB = AE SUMB3 ♦ BASE = SUKB3 ($85 SUMB5 = D0-2-S—R=-l»-6 8BCI = SB786I 2) Il S68II)/0.1194)) . 0 / ) + l 8QI(S86 I I * ) /2 IN 6 8 7 B IS = S87B6C(I) SUM87C/SUM86 = II S8786( 2.0 SUMB3 * SUMB6 = BASE SR88, SR87, SR86, RB85, ) 5 ,1 (5 READ 8B = I + T8688 + II) 8 8 6 8 S = T86B8 SUM87 + SR87 = SUP87 N A) , 5 ( READ E!I) I i I = ) SET!I N 1=1, 35 DO SUK8.7C-S. sup.aa-s—SR88_*.-sup.Ba 0.0 = SUP88 16,5) HRITE U 8 = .0 0 SUM86 = SUHB-5—=- 0.0 T8786C—=—0*0 T8786-»~a.O NO L=l» 1000 DO ED54 ND READ15»4) READ43+S.) A A ED1 0U1 AL1 RL, B2 ALT•RR ' UN'' i ',' N RU ,' ABLET/•SRIR* ABL2, QRDL2, ABL11 DATA HEAD 0RUL1, 1, ELA (O) Q O) RUODI HB8, L86 H88, LBB HIS SLOB6B, HI8683, SL0876, HIB786, I, D O U R QI LOO), P(IOO), REAL*A MLCT RAf. AH Q IA-Ht REALfB.IMPLICIT- ______------ls (I), ------u ______------aaax) — u m * SUM85 1 ______)_.+_.T8786 S86BBI ------______a-X^TDOEV-C-JLECALC.—AVERAGES^.. DOES -2. -PLOTS SR87/SRS6 ------____ ------______1 t ) , -S8766CI ) -S8766CI , ______------, ZI ------______------L,JLSAMPi ,-'LE L| ------SR86/SR88 , ------I ) ______: ------______

------STJ,*UB,'E- / . 0 , ' ■ , 'SET_J.,-*NUMB', ' ER- ,'.JSSUE .tSBLi/ 1 L,.'P.FJVS SOURED '.,t_SRBJL,i7/S : tSfiB7/-SR86.)CJ/) ______------.... ------! ------______176 ------______! ______i ----- __ a ; ! i - i - 1 177

SUFOSC = DSO(I) ♦ SUMDSQ 40-C0NUMJE :------! STOOEV = (blS CRT C SURDSO/ (N -1 .0 )))/1 C 0 0 0 . I i. SDMEAN = STOOEV/ (ESQRT(DFLOATiN) I )------] j hRITE (6 ,1 2 0 ) ! U - 120 FORMAT ('O U ST . OF 1D*10000)**2 .VALLES!) ______j ! \ WRITE (6 ,4 1 ) (OSCI I) ,1 = 1, M ! ! 41-FORMAT—(IB -, 10F11.2J------1 ' WRITE 16 ,4 5 )N,AS786, A8688, A8786C,STOOEV, SOMEAN ! . 45. FORMAT . l.'OAVERAGES C F .* ,I3 ,» SETS ARE... SR8 7/SR86. = ' ,F 12. 8/ IHO,2 0 ------j IX,'SR06/SR88 =',F12.e/lHC,25X,'(SR87/SR86)C = •,F 12.8/IHO,3IX,•STDD !______2EV .=.' ,FL2.a/lH0,31X,.'.S0«EAN .= • ,2X,F10.8)------ic 'r. TRY Tn pi riT-R7/B6-VS. R6/.80 _ AND—1877.66)Ci_\6S_SE.T-S ------1 ______c 1 = 0 .______I ! HI 8786 = 0. | ------00 -53-JJs.l »_A------| 1 = 1 + 1 ______lF-(-HL8XB6-——SB786L1-L)52, -S3, -S3 ------52 HI8786 = S8786II) — .5 3 CONTINUE------1 = 0 ______SLC876—=_1Q0. ------DO 55 JJ = 1, N ------1—s—I—*—1— ------IF(SL0876 - SB786II))55, 55, 54 j 54 SLC876 ,-_Sa7.86(U ------!------i 55 CONTINUE . I 1 0------HI86BB = 0 . ' j ** 7—t_l** = 1 f _ K ■ —, 1 = 1 + 1 ------IF (HIB688--: -S86881.DJ 56.,—57, 53 ______56 HI 8688 = S8688II) 57 ..CONTINUE______:______1 = 0 ------SLCB68--- IPO. ______; DO 59 JJ=1, N =„.I_+_1------:------: IF(SL0868 - 58688(11)59, 59, 58 58 . SL0868 . p -S8688 ( I )______;______59 CONTINUE 1—=—0------HI SRC = 0. !------oo. 6 1 ..j j n ------:______; ’ i = i + i i------IFIHISRC --..S87B6C ID )6Q,_61,-.6I ______60 HI SRC = S8786CII) 61—CONTI NUE------:______1 = 0 '------5LCSRC -=t-100.------j 00 63 JJ=l, N L------1 . -1------I IF(SLOSRC - S8786C(I)i 63, 63, 62 !------62—SLCSRC—=—S87-86CLI-) ------I 63 CONTINUE .------DO ■ 64 -J= 1, 100------— ------; P(J) = S8688(J) ------Q( J 1.= S 8 7 8 6 1 J) ------_ ------R( J ) = S8786C(J) .------64—CONTINUE------CALL PLOTA ( IARRAY,SL086e,HI8688,SL0876,HlB786,l) i------CALL PLOTB. (P( II ,Q( 1) ,4HC00X,N)------' CALL PLOTC

CALL PLCTA ( IARRAY#A8LFT, AQRT, SLOSPC,HI SRC»1 ) -CALI PLOTO -( SET ( 1) *R I D , 4HCOOX*NI ------CALL PLOTC (HEAD1,9,0RDL2,7,ABL2,31

jc BEGIN SECOND LOOK AT DATA

DO 140 JJ=1, 2 -TOT-2—=-0*0 ------:------T 86882 = 0.0 . T37B62--= 0 .0 ------j K = 0 | WRITE ( 6 ,6 6 ) ------! 66 FORMAT ( 1H1, 'THE FOLLCWING (SR87/SP86IC VALUES DIFFER FROM THE MEA LN _BX_K ORE THAN—T WICE-THE-SIO-DE-V-D ------00 70 1=1, N DIFF =-DABS(S8786CtI1-AB706CJ ______IF(0IFF.LE.(2.#ST0DEV)> GO TO 65 WRITE-.(6 ,67) -1 S 8 7 8 6 C .H .) ------67 FORMAT (IHO,I3,F15.6) SRC2 (J )—=—10011.------GO TO 70 -65-K- = ..K _ ± _l_ SRC2(1} = S8786CII* - J 0 T 2 . = .SRC211 )._*_TXir2 ------T87862 = S8786(I ) ♦ T 8 78 62 —186882—? SH6S8 ( L )_* -1 8 6 8 fl2 - 70 CONTINUE ASRC2- =-T0T2/(K*i.»- IF (ASRC2.E0.A8786C) GO TO 145 S 0 5 Q 2 = - 0 .0 ______DO 100 1=1, N IF. I SRC2(.LI_-—10QQ^L9.9»__aa^_58_ 98 DSQ2(I) = 0.01 GO.TO.100______99 0SQ2(I) = ((SRC2(1I - ASRC2) * 100C0.)**2 SDSQ2 . =_SD-SQ2. t . DSQ21 L)______100 CONTINUE -A87862-5-18.7.862/(ICtLU- A36882 = T86882/(K*l.} STDEV2 = I OS CRT I S 0 S 0 2 /.I I DFLOAT IK. J ) - J .. 0 ) . ) 1/10000.0, | SDMFN2 = STDEV2/tDSQRT tDFLOATIK))) WRITE (6 ,1 20 ) WRITE (6,41) (0SG2CI 1,1 = 1, N) -WRITE--!6 ,-LlQ.J- 110 FORMAT COTHE FOLLCWING ARE RECALCULATED VALUES AFTER REJECTION OF 1THE SETS -LISTED ABCVE' )------'------—------WRITE (6 ,4 5)K, AU7862, A86882, ASRC2, STDEV2, SDMEN2 . STDOEV.=-STDEV2------140 CONTINUE —145-.WRITE-I6 ,13 0)------130 FORMAT ( 1H1) -1 0 0 0 CONTINUE------CALL EXIT ------END------RUN 2100 SRI R. 506 SOUTH 0T2-H0N., NILSEN MTNS. 5-29-70 16 SFTS 179 180 > i L L L l i L U . L i i . i 1 . 1 . 1 i i i . i ii i j 036* . . 1-511 ; .10-3561*1 .. . 10-3661*1 1111 © e i.i i . 9 1.1111 © /t* /t* © © 11111 it J n i l l i i.i i i.i u.i Li.i-UUJ. 111 U.LL! ______♦ ot-yr-s- 1.0-3261*1 ------3iva >» U .88BS/98BS.03BnSV3K V U O 11 i.n n.I Ljm LLI 111 10—3VIS*6 - mas m _ i i o-.ast***_ m _ yes** *,r»& ' C.Q'rt SRI A DATE f-Z I-IO C 9.519E-01 ---

r

a ’VAAJE-Ol'

97 * 28E-oi' 11111 n n i t i f i i i i fi ri rn i i i ri i T ffi i 111 rrn rm n i 11 nrr f n i m (Tj 11 r n n n n 111 n i n n 111111 t t i u 11 rr- 181 ~ 0 0.0“ ' 3.700E 00 ' ‘ 6.*00E 00 " 9.600E 00 1.280E 01 " 1.600E 01 THE FOLLOWING ISR87/5R86)C VALUES DIFFER FR[]M THE MEAN BY M.1RE THAN TW1CF THE STD DEV

10 0.967950 irST"flF'"(0*t 00001**2 VALUES . " ...... ' * " 561 .74 166.06 0.05 167.65 689.89 668.69 30Z.33 153.15 566. 99 0.01 1802.11 1200.6R 16.26 730.32 2.60 10.09

THE FOLLOWING ARE RECALCULATED VALUES AFTER REJECTION OFTHE SETS LISTED ABOVE

AVERAGES OF' 15 'SETS'ARF.;.' SR87/SRB6'-* 0.R6A0T015 ...... ' ‘ * ...... “

SR96/SR8B * 0.11066566

(SR87/SR86IC ■ 0.96632836

------* STOOEV -"0.00212806 " "" ...... *

SDMEAN ■ 0,00056966 XRF Program to calculate (Rb/Sr) Intensity Fortran IV G level 18

Input data: J= no. of data decks to process Title of deck

K= No. of samples in deck THETA1-5 = 2-theta positions, in increasing order XFACT = conversion factor between (Rb/Sr)j and (Rb/Sr) ppm XFACTE =

TSM1-5 = seconds at each 2- theta position CSM1-5 = counts at each 2-theta position Variables calculated: ARBSRI = average value of (Rb/Sr)

STDDEV = f-f‘ of average value of (Rb/Sr)j

SDMEAN = If of average value of (Rb/Sr) j

the remainder is similar to "ppm by XRFuc DAMON Curve" program FQRMAT_I_2AA 0 3 3 ______. ______PE A SR. ^ IX M MPLE _SA ' AT_.(././/_ Jt3A_F0RM : ______:

______DIMENSION TSH(1Q»* DIMENSION TSH(1Q»* ______A AN LI ______<■» n 1 6 2 3 FRA (0, FOO I 5FIO.O) FORMAT (30X, 333 3 FRA (IO 2HT =•,X, X,52,5,5.2,5,F5. 5X, »X ; 2»9X, . 5 ,F X ,5 .2 5 F 5X, , 2 . 5X,F5 , ,F5.2 5X , 2 . 5 ,F ,6X • = '2THETA IHO, FORMAT ( A33 2.5.. 0 OMT lO«"F RGA T CL (BS)N, IER AEIE ) ! •) BASELINE LINEAR PROGRAM (RB/SR)INT, CALC FORMAT TO tlHO,«x"RF 10 1 OMT 1I7HRY AA AE SML NMS R O. N. F STDS OF NO. SAMPLE NAMES DATA NOS., OR DATE, FORMAT t1HIt79HXRAY 11 12_.F0RMAT_ (.13.1 12_.F0RMAT_ I'.XFACT CONTINUE NT R,I • T DV (TE) DEN/H 8X» SDME ,86X,» SDMEAN'/lH Z(STDEV) DEV STD ,• X I2 SR1, NET 3 6* /PX.' B ' . 26 * X /IP LAN LS._5.am PkE.S_U LS._5.am NETR8*, ( SR)*, •VR/P 1,• R7S8• X• RB87/SR8 1X,• SR87/SR86•, • I,1X, ' ,•AV(RB/SPI X ,2 )I* R /S B (R ,' * 8 R T E IN _REAL*R. WPIT tI WRITE,E RBRG._E_3BtJA.CK* PH._PS .^O .__PS(2J 2 0.__*_CP.SM( ..T^.O. ) 3 ( CPXH,.=_CP.SM FORMAT. RBBACKTHETA5-THETA3J ._= (THETAArTHETA3)/( RBPK. BRNN) RP/RK ; RBPK/SRPK = RBSRIN(NX) £LP.SJ1.U L_i=_£.SJiUJtZJLIS fUJ.l=P.x5QE=J36_*_C5M.LIJL> £LP.SJ1.U L_i=_£.SJiUJtZJLIS RSI=R.RNN)» RS TRBSRIRBSRI_=_RB.SRININX)—» I R AK (THETA2—THETAl)/(THETA3-THETAI) SRBACK = RG SBC*CX-PM «CS l i SRBACK*(CPXM-CPSM< (l) - SRUGm«-CPSM K 1, = L 999 00 P E IREAD, . ) AII t i f READ (IREAD, (IREAD, READ DO IWRITE, ( WRITE R K CPSM(2)-SR0G = SRPK ED_J.1R _ READ .l, A T jm ) 3 3 .,A E L I R WP.ITF_(JW IKRI.TE_=_6 DD I1J 11WRITE, WRITE 0 0 0 1 DO ED IED2) ,HT1,HT2 HT3 HTA HT5XAT FCE , THETAA, THETA3, ,THETA2, THETA5.XFACT, XFACTE K,THETA1 (IREAD,25) READ E D IED 11 J 121 IIREAD, READ TRBSRl R PORM O AC (R/R T GR8/R6 VER GIRB87/SR06) I NT. RB/SR) PROGRAM” ( XRF CALC- TO RA = 5 = IREAD MLCT EL8 IA-H.O-Z) REAL*8 IMPLICIT READ. 6 11 5 1=1, 261 II 1, = NX 99 t

______.READj. 1_T 3 3 j_.3 D A E j.IR . ) .J 0 ° _H. . CPSM(A.).-RBBG SPEC M = 1, 1, M = .3j (.13 E A 3) St1 _S(2) C ES M CSMt ), AD1) 2 ,_CSH( j 333) FJ0.8, X. .X ,2 ..8 0 J .F ^ ______16X, ______,2X, ,2X,

iE _.E2TH AL .F.2,H.A. H .AtHTA,H.A,.H1__ THE J.AA.tTHET.A5,JHC.TAQ,..LHE1A_ ,THE.TA3., T.HFJ.A2 TA L, »_S.PEC2xT.HC I ______ACK.ULL._3ACi

1 0 3 3 p jUEISL. (CPS tt< t q _ l _ : ______3 i 1 43A J j 2£12tfll l f t 2 1 £ i2 .jL 7 _ F 5 3,7£x.10x6«.LQ_X. 1P._91 6 F x 0 xF. 1 £ 7 13., ______SPEC1, SPEC2, I I , S87B6C, S87B6C, , I I SPEC2, SPEC1, ______l ______CS.MUO) SMil.) J.-C S ,. LQ.AJ .,A Q JL .,..E _ = S 0 L L ______

PXfcLLtC PXfcLLtC : ______THETA2 , __.Ia_.. MlJ MI) _TS.Mi^J M.IA). T S ,_ I _ , M.l3J 5 .1 t_T_S.MI.ai_,. , _CPSM( ,_RBSRI N( 10) 50) ______J ______; ______PXH lj)4CK 12J lj)4CK THETA.3, ______31,_C S 1., C MI_ .3 .A( 1_, .S _C H (_5_) ______K±j THETAA ,THETA5 . XFACT. XFACTE ______JOX, .. X* 5X.» j R »E 0. .p AXX15 _ . , * _ J.O X , AC.PJ ) L3J^5JtxJ _L X C j)A aA.CK.lPBJ ______S8786E . 501 0 I5 Q S J t.J : ______0 7 - 9 1 - 5 ______: ______184 ' i ___ | ; \ ; ; 1 I | j ! ! ! ; 185

WHITE tlWRITE, 435) SPEC1. SPEC2, CPSMl2)t CP SHI 4 ) t R8PK* RBSRININ .)X),_.CPSHi 1lj_5R.B0i_.CP5H13.L» Sh'L511__5R£K„ 435 FORMAT 11HO.2A4, 1IX,FI 0 .2 110X,F10.2,15X,F10.2tF12.6/10X.5F10.2,5X»F 110.2)______99 CONTINUE ARBSRI _= TRBSRI/_LNX*JL*J ______SUMDSQ = 0 .0 o n . 40. J. - 1 , . NX ______:______05Q,( I ) = (R8SR1NI I )-ARBSRI ) * * 2 SUHOSQ_«..DSQ(l)tSUH0SQ______40 CONTINUE STDUEV..=_DSQRT( SUHDSO/.INJC-U 1.1_____ IF IS87B 6C.E0.0.0) GO TO 41 S WiEAN_S_.SJ.DDE V/.OiOR J.LDF_LXlA.TJilXil. RBRAT = 0.2785/85.46B07333 5R.878B = SQ7B6C * 0.1194 ______SRSUH = 0.0067854114 «- 0.1194 + SR8738 *■ 1.0 __A8SRB4„= .0.006 78 541 14/SRSUH ______A8SR86 = 0 . 1194/5RSUM AB.S ? 8 7 = SR 87 8 87.S RSUH ______ABSR88 = l.O/SRSUM WT.84_=„ABSR 84. *_.83.913.43 ______WT86 = ABSRH6 * 85.90929 WT87-_=..ABSR8.7. # 3 6 .9 0 0 3 9 ______WT68 = 4BSR88 * 87.90564 ______A.TWLSfi_=„HI8.4_ £ WT86 +_.HTB7_» WT8B CONFAC = I0 .2 7 8 5 /8 5 .4 6 8 0 7 3 )* (ATWTSR/ABSR86) „RBSR A.T.. s. .t.ARB SR I *XF ACLW .ONEAC ______| CFACTE = 0.28333333#S8786E I______THING=I.XFACTE/XFACT ) **.2M S0ME4N/.ABB.SR,L1**2£ IC.FACIE/XQNE4CJA5Z. | R8SRAE « 10 SORT( THING) ) *RBSRAT I___ 4JL_WJELU.f ^L L H R .lJ£j_43j») ,,.ARB.S.R1.> -S8.Z86G_t. 1. SOHEAN 4.36..F0RMAI_t 1H..J 81X.F12.6 ,£1I..6,F 12..6/.1H_»MX. FIQ.J. j JX j U i l . 7 , ZX j FJ jO. ZA. 11H ,84X,F10.7) _ 9 9 9 . CONTINUE ______WRITE (IWRITE.437) _43.7..EQ8HAT_t LUU ______1000 CONTINUE CALL_EXLT_ END 1RCLL VCLS... LAST CGHR. 18 JUNE70 .XRF PRCCKAt'. TC.CALC JHB/SK) INT. LINEAR BASELINE

2THETA ■ . 35.00 35.85 35.92 37.99 41.50 XFACT - 1.28396788 +CR- 0.01952020

SAFPLE _ SR PEAK R0 PEAK NET RB (RB/SRIt AV(RB/SR11 _SR87/SR86 _R887/SR86_ BACKI1) BACK t SR) BACK 12 I BACKtRB) BACK(3 ) NET S R * ' ~ STO CEV 21ST0EV) SOFEAN SOFEAN

484 464.51 217.80 54.68 0.20C448 ------j 206.02 191.72 . 173.72 163.12 128.36 272.79

484 461.01 .”. 216.47 54.05 0.201505 i 208.27 192.77 173.27 162.42 126.86 268.23 ! 484 464.61 218.70 56.43 0.207016 i 207.27 192.03 172.85 162.27 127.57 272.58 » ! 484' 465.91 ' 217.52 55‘. 44 0.201544 ; 205.02 190.85 173.01 162.09 126.24 275.06 i

! 484 _ _ _ 469.21 226.03 54.08 0.204582 j " 221.52 204.85 183.85 171.94 132.88 264.36 i

I 484 465_.3 l 226.78 53.83 0.205491 218.27 203.36 . 184.58 172.95 134.78 261.95 1 0.2C3431 0.728173 0.757675 ] 0.0026302 '0.0038000 0.0121965 ____ ! 0.0010738 • i 486 537.34 416.79 249,62 0.730810 t 209.72 195.77 178.22 167.16 130.91 341.57 1

486 536.44 416.44 247.23 0.731493 I * 212.72 198.46 180.52 169.21 132.11 337.98 I 486 5 39 L 85 414.99^ 245.40 0.718120 | i 211.22 198.12 . 181.62 169.58 130.11 341.73

! 486 543.85 _ _ 423.29 247.74 0.732116 219.72 205.47 187.52 175.55 136.31 338.38

4E6 538.54 415^65 245.91 0.725772 ______214.82. _ .199.72 ...... 180.72.. 169.75 ... 133.76. 338.82 0.727663 0.744555 2.714499 | 0.0058965 0.0028000 0.0424307 _____ •

0.0026370 186 187 Rb and Sr ppm by XRF and Damon Curve Fortran IV G Level 18

Input data: J - No. of data decks to process Title of data deck MNOSTD = No. of Stds. used THETA = Degrees 2-theta of the seven positions used (in increasing order)

STD1,2 = Name of stds . SrX, RbX = Concentration (ppm) of Sr and Rb in standard

SMOKA^ 1 ” Seconds counted at each 2-theta position for TS1-5 ) standards, in increasing order

CMOKA^I = founts measured at each 2-theta position for 1 standards, in increasing order

K = No. of samples in deck SPEC1, 2 = sample no. SR8786 = Sr87/Sr86 value for sample R7 flfi SR8786E = 2 d for Sr /S r measurement TSMOB, TSMO, TSM 1-5 = seconds at each 2-theta position for sample (increasing order)

CSMOB, CSMO, CSM 1-5 = counts at each 2-theta position for sample (increasing order) Computed variables for standards: SRBACK, RBBACK, = Fractional distance of K peak from low 2 -theta background relative to distance between two adjacent backgrounds

CPSST ) CPSM O ) = C°unts per second (CPS) for 7 positions of \ standard, corrected for counter dead time CPSMOB ) 188 BACKMO = fract. dist. of MoK «: C peak between backgrounds PKMOKA = net cps of MoK

CPXST - cps of background between Sr and Rb, adjusted for overlap, if any SRSTNT )_ Net cps of Sr and Rb K peaks, adjusted RBSTNT ) for a linear background

SRMO = j /*MoK ' C RBMO, ZK' - SRFACT* _ Slope of best fit straight line in plot of RBFACT IZK,, / I MoKr< c v s . ppm Z SRALFA pi . i RBALFA. - sl°Pe + 1

SRBETA' _ „ .nat i RBBETA ‘ Sl° pe -1

Variables calculated for samples:

ciwr^DQ \ °PS for ? positions of samples, corrected for SMBCPS) counter dead tlm e BGMO = cps of background calculated beneath MoK •* C

PKMO = net cps of MoK*: C CPXM = cps of background between Rb and Sr, adjusted for overlap, if any

= °PS BG calc, for Sr and Rb K KBBtj.

R B ^ ) = net CpS an<^ ^ RBSRI = ratio of net intensity of Rb and Sr

SRMOLY _ T /T RBMOLY ZK c /AMoK ■: C 189 QDOT noor/^ ' = '’" ° t °PS measurement for Rb and Sr K peaks RBSIG^

RBLMDT ” l° wer limit of detection (ppm)

SRDEV \ _ of ppm determination, based on of cps meas- RBDEV . urement only, not on

' RB £ SR ‘f f H“ b y "x RF £ OAHCN“CURVE*.' LINEAR BACKGROUND VER. F

I FPL ICI T REaW (A-H tC-ii REAL*A SFECl,SPEC2,STCl,5TC2.TJ-ETAl,TFETA_2tTHETA3rniiT*./'»-THETA5i I»i ' 1ET AC, THE TAP L‘ tFENS ICN CS(10I.TS( 10),CPSST(IC),CSF(1CJ,TSF(1C »,CPSF( 1C),SRFC(90 "l)i RBPQKO), STCK9C), STC2(9C), SRX(9C), RBXI9C), SRe7e6(2CCj, SP 2EC112C0 ) i SFEC2I2C0). PFFRE(2CC). PPFSR(2CC), KESRAT(2CC), RBFOLV( 32CC), SRFCLY(200)1RBSR 2C(T) ~ " IREAC = 5__ 1______IWRITE = 6* R6AC (IREAC, 12) J______12_ FCRFAT (13) _ CC_lCCO H - It J ______;______fix = 0 READ (IREAC,1 1) ______ll'FCRPAT ( 1H0• 79HXKAY DATA CATE. SAPPLE NAFES CR NCS., NO. CF STOS 1£ SAFPLES USED, ETC. _ ) ______HEAD (IREAC,13) PNGSTCrTHETAC, THETAF, THETA1, THETA2, THETA3. TH 1ETAA, THFTA5 ______;______13 FCRFAT (i3,2X,7F7.2) SREACK = (THETA2-THETA1)/(THETA3-THETAI)______RBEACK = (THETAA-THET A3)/(THETAS-TFETA3) REAC (IREACr 135) 1STCK1). STD21I). SRXH). RBX(I). 1 = 1, FNCSTO) 135 FCRFAT (2AA, 2X, 2F1C.Q) ViR 1 TE t IVRITE, 10J______1C FCRFAT (*l ***** RB/SR EY XRF £. CAKCN CURVE ***** •) WRITE (IWRITE, 11) ______!______,______WRITE (1 WRITE,8) ThET AC ,f)|ET AF,THETA 1,THETA2,THETA3 ,THETAA,THETA5 fl FCRFAT (//•C2THETA =1,7F1C.2I______WRITE (IWRITE, 7) 7 FCRFAT ( ■OSAFPLE*,15X,'PC PEAK^,13X , •SR PEAK*,13X,»RE PEAK«.19X.«R IE FPF " RGSB LFCT RB/FC/* SRE7/SR86 BG(C) FC BACK _2 BG(1) SR BACK BGI2 L **B EACK BG(3)*/* 2(SIGFA) * ,7B X , 3 1 SR PPF ' SRSC “ LFCT SR/FQ*/' RBe7/SR8'6*, 13X, »F0 CPS'.IAX,' ASR CPS!_,1AX,'RB CP_S'/' STD OEV.aSX.'SR SIC’.IAX.'RB SIG',A6X,«R 5B/SR' ) ...... * WRITE. .(.IWRITE,9.) ______9 FCRFAT ('0*+******* ***** ****** ***** ****** *** 1** *««*** • * * * * _ ****** *♦*♦ **** »»♦*»«) DC 15 N" = I, FNCSTO" REAC (I READ ,26) SFQKAE, SFCKA , TS (1) , TS ( 2), TS ( 3 ) ,IS (A) ,JS_( 5)______26 FCRFAT ( IOX,7FIO.O) REAC (IRE AC , 26 ) CFDX AE, CFCK.A , C S J . l > ,*CS ( 2 ). CS ( 3 ), CS (A ) ,CS (5 )______DC 13C I » 1,5 c f s s t (I) = csm/(rstn_-_c.5CE-_C6_ * c s i m ______13C CONTINUE CPSFC a CFCKA/(SF0KA-C.50E-C6*CFCKA)______CFSFCB = CFCKAB/(SF.CKAE-0.5CE-C6*CF.CKAE> BACKFC f (TFETAF-TFETACJ/tTFETAI-THETACJ______>KFCKA'*‘CPSFC-IBACKFC*(CPSST(1l-CPSFOBMCPSFOB) CPXST = CPSST C3 I - 0.0 * CPSST(2)______SRSTM = CPS5TI2)-(5REACK*(CPXST-CPSST(i))+CPSSTIl)) RBSTM = CPSST(A)-(REEACK*(CPSST(5 )-CPXST l+CPXST)______SRFC(N) = SnSTNT/PKFQXA RBPC(N)_= HESTM/PKFCKA______' 15~CCM1NUE SLFA = C.O ______DC 16 A - 1, FNCSTC SUFA = SLFA ♦ SRX (N ) * *2______16 C C M I N U E SUFC =» C.O______DC 17 N 3 1, FNCSTD SLPC = SLFC ♦ SKX (N ) *SRFC (N ) ______17 C C M I N U E SUFC 3 C.O ______.„. . 191

DC 18~N = 1* FNCSTO SUFC = SLFC ♦ (SRFC1M ♦ SRFC(M)______liT'cCNT INUE SRALFA - S U F A /S U F C ______SRGETA « SUFC/SUFC SRFACT * ( SRALFA + 5RBETA1 / 2 j ______SLFE = 0 .0 CC 22 N = 1, FNCSTC______;______SLFE « SIFE + REX(N)**2 22 C C M I M J E ______SLFG = C.O DC 23 K = 1« FNCSTC______SUFG = SLFG ♦ RBX(N) + RBFO(M 23 CCMINUE______;______SLFH = 0 .0 CC 24 N : If FNCSTC ______SLFH = SLFH + (RBPG(N) * REFC(M 1 24 CCNTIMJE_ .______REALFA = SUFE/SUMG REBETA = SUFG/SUNH______REFACI a (REALFA * REBETA 1/2 READ IIREAD,_251 K______25 FCRFAT 1 13 I . _ DC 999 . L. = It__K ______NX = KX •* 1 . REAC ( IRFACf 3311 SPECl.(NX.).,.SPEC2LMA».SR£J.86J2{XJt1_SJ7£6£______331 FCRFAT I 2A4, 12X, F 10.6.ICX,F10.8) REAC 11R E AC, 3 32 ) TSFCB, TSFC , TSF (1.), T SF C.21 T SF.13 ). t TSFJA1 .5>______332 FCRFAT (1CX,7F10.C) READ IIREAD,3 32)_CSFQE,(CSFCfCSF_(_lJ,CSF,(.2.l_,_C5MI3J.t.C.SFJ_AJ_*CSFI5.) ______DC 261 1=1, 5 ] ! CP SF 111 = CSF1H/ITSFU )-0.5CE-Cfe ♦ CSF(Il)______;______| 261 CONTINUE ' !_____ SFCFS = CSFC/(TSFC-0.50E-C6*CSF01 ______;______“ "SFBCPS " = CSPCB/(TSFCE-0.5CE-06*CSF0B) [ EGFC = EACKFC*tCPSFM)-SFECPS)*SFECPS ______PKFC * SFCPS-GGFO ______CPXF =_CFSF(3) - C.O * CPSF(2) ______SRBG = SPEALK*CCPXF-CPSF(I)i+CPSFI 1) REHG = REEACK*(CPSF(51-CPXF)+CFXF ______~...... SRPK = CFSF (2 l-SRBG j RBPK = CFSF (A l-RBBG ______! RBSRI(NX 1 = REPK/SRPK SRFCLVINX) = SRPK/PKFC______! ______KBFCLYINX) = RBPK/PKFG * j PFFSRINX) = SRFACT*SRFCLYINX) ______:______;______PFFRBINX) = RBFACT*RBFCLY(NX ) _ THFC = C5CRT (CPSF(1)/TSF( 11J______1 ThSR = CSCRTICPSF(2>/TSF(2)) j IWSX » CSCRT (CPSF(3)/rSF(3]J______! ' TNRB' = CSCRT(CPSF(Ai/fSF(A>) * TWSV * CSCRT(CPSF(S»/TSF(5n ______SKEGSC = DSCKT( ThFC* + 2 -* Th$X**2t ( REBGSC = CSCRT1ThSX**2 + THSV**2) ______j SRS1G = CSCRT(ThSR**2 + SREGSC**2> j KE5IG » CSCRT (T!»RE+*2 ♦ REEGSG**2) ______~ SRLFCT = (3*FFFSR{NX1*SRB0SG»/SRPK RBLFCT = (3*PPFRli(NXI*REBGSGI/RBPK ______; SRCEV = (SRSIG/5RPKI+FPPSRINX) RBCEV a (RES(G/RBPK1*PPFRB(NX)______; IF tSR07fc6(NX).EC.C.O) GO TG 27 _ SR37B8 = SHE 786 (NX) * _0 . 1194 ______SPSLF = C.CC67054 ♦ 0.1194 * SRE7E8 ♦ l.C ABSKB* = C.CC67854/SRSIIF ______' A GSR 86 = 0 . 1 194/SRSL'F AESRB7 = SRB/H8/SRSUF ______— r 0 n 1 J l 1 1 i j n m N 'fO 0 1 n o o fO I »-• o «o ifo ro ro 1 n u> * 1 0 : *- -VI *0 Ui J) i® - J > n n ro X lA ft X xnxxxxxnxoxoxnxx «• .n x x o x x n x« T> n : X • n 7 x x 9 n » ro x x ® ro -4 -* m —4 ro NJ X *— ^ 3 n n 3 3 -H ? r * 0 X X a X * - in — > tr Z T CD ro m CO in r H 1 CD H tt ^ H-*X^-H-H-HMX^X-*X-JX—l-H *> *t *H ^ TP -H *« H * •H -n Tl m liJ — X ^ X ^ O 9 Tl —»ro *0 O' 9 x> o* m o t> rr. m>mrnmmmi>m>fTi>m>mm > o m m z> m m i» m J m ** 9 m > m t» ft *4 ti. 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» . I General Standard Deviation calculation

Fortran IV G Level 18 Input data: ND = No. of data decks to process Title of data deck N = no. of measurements to be averaged

SAMI-3 = sample no. X = individual measurement Variables calculated: AVGX = Average of measurements DIFF = Difference of measurement from average SUMD2 = Sum of squares of differences STDEV = Standard deviation (d') PCTSD - Standard deviation as a percent of average

SDMEAN = ^ of average ( ) PCTSDM = as percent of average 196

;C GENERAL STD DEV CALC. DATA DECK IS AS FOLLOWS... j;______nd = no . of pecks n format ______,C HEADING...70 SPACES, LEAVE CCL. 1 BLANK 1C______N =_Nn OF POINTS_ ___ 13 FflP^AT______„ C SAN°LE NO, 12 SPACES 3AA FORMAT... X VALUE, IN COLS 21-35 USF DEC' C______„F15,R.____ FORMAT._RFPE.AI_ THgSF._CAR_.QS .I.TIMg.S ______■______'C """HEADING CARD C*f’ NFXT DATA SET. . . .ETC. .£ _ ------IMPLICIT REAL*fl (A-H,0-ZJ ______REAL*A SAMI f SAM2.3AM3. ______;___ DIMENSjON SAMLI100 ),SAM2t10 0 1,SAM3I 1 0 0 ),X( 2 0 0 ) ,DIFFI 2 0 0 ) ,DIFFSOt200

REAH'TsiTorim ■ " ■ 10 FORMAT 1 1 3 )______DO 1000L=1, ND :______R£AP__L5j ?Q.)______20 FORMAT (IH O ,‘ TITLE OF DATA.. .7 9 SPACES OF INFO. LEAVE CDL. 1 tJLANK l______:______l>------:____ WRITF (6 ,2 0 ) WR I TF ( 6 .3 0 ) 30 FORMAT I//IHO,' SAMPLE* .25X, *X VALJE ‘ ,9X, U X I-I X AVG) • ,9X, ' (01 1FF)**2‘ ) 1 READ (5 ,1 0 ) N TOTX - 0 .0 ’ on 100 1=1, N • READ ( 5 , AO) SAMim.SAM?m.SAM3(II,X(I) ------_ ...... AO FORMAT (3AA, 8X,F15.8) ______TOTX = TOTX i- XI U______:------I 100 CONTINUE i______AVGX =-_T.QTX/N_ .:______SUMD2 = 0 . 0 :______on 200 1 = 1. N______, DIF-F(I) = Xtl) - AVGX I______ryjfESQt_JJ__-^D.LF_F t i l * *2 ------:------; SUMD2 = SUM02 + DIFFSDII I :___ ZPQ-CO.NT.I-NUE______.------STDEV = DSORTISUM02/(N -l. 0 ) I *______PCTSO = 1 STDEV/AVGX ) * 10Q..Q ______SDMEAN = STDEV/IOSORTCDFLDATCN))) ■______E£LSPM-J5-,IS D!dEAN/Ay.GXL*lQO.JO------, WRITE 16,50) 50 FORMAT I IMP)______------WRITE (6,60) (SAMi(I),SAM2m,SAM3(I),X(II,0IFFCI|,DIFFS0(I), 1=1, 1 N)------:------60 FORMAT ( 1H0 ,3 AA, I OX, BX, F1 5 .ft, 5X, F 1 5 .3 ,5 X,0 1 5 .6 ) :_ WR1T.E_.t .6,1 0 )„Nj J 0 r X, SUM.D2., A VG X,.STDE.Vj PC T S0, SDMEA.N, PCT s DM ...... 70 FORMAT I//1H0,*N = ',I3 ,1 5 X ,‘X SUM = • ,F 15.3 , 11 X,' SUM OIFF**? = __1D15.6/JH0,22X ,JX. AVG. F LS...H/LUG,2GXS TD _DE.V = > F15 ■ 8/ 1H0, 12X, . ,—— . 2 ‘ PFRCFNT STD DEV = ' , F 1 0 .3 /lH 0 ,2 lX ,• SDMEAN = ■ ,F 1 5 .3 /1H0, 13X, ' PERC —3 ENT SDMEAN = ‘ .F1Q.3J------WpITF (6 ,8 0 ) BO -FORMAT,_(JiUJ______:______1000 CUNT INUE ______CALL EXIT______;______:______END *05 XRF DMA SUM 23JUNE70

SAMPLE X VALUE m - i x avc )

0 .7 1 3 0 1 0 0 0 0.7710830-05

0.733R 2300 0.3870810-05

C .73900000 C.C0320956 0.10 30130-0*

7 90 3990- 072 6 9 0 0 0 0 0.0C 8R90** 0 .7 9 0 3 9 9 0 -0 *0.7

0 .7 2 7 0 0 0 0 0 0.77271R0-04

0 .161531D-03

8 2*2 390- 076 * 5 0 0 0 0 0 .8 2 * 2 3 9 0 -0 30.7

*05 0.9802890-03 0.5013320-03

2 1 875 70 - 001*790**. 2 1 0 0 0 0 0 1 * 7 9 0 * *0.7 0 .2 1 8 7 5 7 0 -0 30.0

0 .7 3 0 1 0 0 0 0 0.0C 5650** 0.323R110-0*

0.7778770-03

0 .7 3 7 6 0 0 0 0 0.00180956 0.327*520-05

0 .7 3 3 1 0 0 0 0 0.7238*50-05

0.378*730-05

0 .7 5 5 8 6 9 0 0 0.02007856 0.A03U9D-03

16 X SUM - 11.7726*700 SUM D1FF**2 « 0.*092070-02

X AVC *

STO DEV PERCENT STO DEV - 197 SOHEAN - PERCENT SOHEAN 198 Appendix B: Sample Descriptions (Using Classification of Williams, Turner, and Gilbert, 1954)

Pensacola Mountains: Samples collected by D. L. Schmidt, U.S. Geol­ ogical Survey, Federal Center, Denver, Colorado O .S.U . No. 290 (Schmidt No. W 21d.12.27.63) Gambacorta Formation, Red-Brown Member, Bragg Valley, S. Neptune Range. Rhyolite, grayish red with prominent red-brown flow banding. Porphyritic, with highly embayed quartz, and pseudomorphs of sericite after feldspar. Inclusions of altered pumice.

291 (Schmidt No. N l. 12.24.63) Gambacorta Formation, lower Member, Upper Jackson Valley, S. Neptune Range. Latite, aphanitic, greenish- gray, with dark greenish-gray streaks.

292 (N 2.1.12.64) Gambacorta Formation, Hawkes Porphyry Member, west side of "Hawkes camp" valley, S. Neptune Range. Porphyritic quartz latite with phenocrysts of K-feldspar, plagioclase, and quartz in a dark red groundmass.

293 (S 25.12.29.64) Gambacorta Formation, Hawkes Porphyry Member, middle "Bragg" valley, S. Neptune Range. Same as 292 except more phenocrysts (33%).

294 (S 2-11.12.63) Pyroclastic rhyolite, autolithic breccia, from basal part of Elliott Sandstone, Pemberton section, one mile west of Wiens Peak, S. Neptune Range.

348 (45 Sa.13.12.65) Gambacorta Fm., Hawkes Porphyry Mem., Hill Nunatak, Neptune Range. Rhyodacite, phenocrysts (20-25%) of quartz and altered K-feldspar in a greenish-gray aphanitic groundmass. 349 (73 S .17.12.65) Gambacorta Fm ., Hawkes Porphyry M em., east face of Mount Hawkes, Neptune Range. Rhyodacite* similar to 348. 199

350 (46Sa.13.12.65) Gambacorta Fm., Hawkes Porphyry Mem., Hill Nunatak area, Neptune Range. Rhyodacite, altered, olive-gray vitric-crystal tuff. Quartz (30%), alkali feldspar (10%), and plagioclase (15%) are identifiable.

351 (46 Shl3.12.65) Gambacorta Fm., Hawkes Porphyry Mem., Hill Nunatak area, Neptune Range. Vitric-crystal tuff similar to 350.

389 (23 S .28.12.63) Gambacorta Fm ., Red-Brown M em ., upper Bragg Valley, Neptune Range. Vitric-crystal tuff? Quartz and plagio­ clase in aphanitic groundmass.

390 (21 W a.27.12.63) Gambacorta Fm., Red-Brown Mem., Bragg Anticline, Neptune Range. Vitric-crystal tuff? Similar to 389, but with light and dark bands.

391 (5N.12.1.64) Gambacorta Fm., Johnston Porphyry M em ., eastern Hood Ridge, Neptune Range. Black ash flow tuff, phenocrysts (33%) of quartz and plagioclase.

356 (47Wa. 28.1.64) Hypabyssal porphyry intrusive into Patuxent Fm. at Pope Nunatak, 120' diameter plug. Porphyritic felsite, pheno­ crysts of quartz, K-feldspar, and plagioclase. Black angular inclusions.

352 (12 Sa.11.1.66) Rhyolite, east prong of Gorecki Peak, Schmidt H ills, Neptune Range. Light gray vitric-crystal tuff? Quartz and K-feldspar grains are abundant (60%). Black angular in­ clusions up to 1" long.

353 (32 Sa.7.2.64) Rhyolite plug (-~ 100' diameter) intrusive into Patuxent Formation, Williams Hills, Neptune Range, Phenocrysts of K-feldspar (15%) in a aphanitic groundmass. 354 (12.Sb.11.1.66) Rhyolite, Gorecki Peak, Schmidt Hills, Neptune Range, Similar to 352.

355 (32 Sd.7.2.64) Rhyolite, Williams Hills, Neptune Range, Different Outcrop, but similar to 353. 200

357 (18.SB.5.2.64) Felsic tuff, east-central Williams Hills, Neptune Range. Numerous black angular inclusions (25%) in gray aphanitic rock.

358 (W 44a.23.1.64) Rhyolite, Gorecki Peak, Schmidt Hills, Neptune Range, Similar to 352, 354.

434 (1 Se.6.12.65) Rhyolite, Williams Hills, Neptune Range. From area 1% miles west of 353,355. Part of shear lense in folded Patuxent Fm. Quartz and plagioclase phenocrysts and minor K-feldspar. Sericite (?) abundant in groundmass.

435 (1 Si. 6.12.65) Rhyolite, Williams Hills, Neptune Range. From area lk miles west of #353,355 . Similar to 434. 414 (Schmidt's No. S23-24B.2. 7.64) Basalt, Patuxent Fm., Williams Hills, Neptune Range. From interior of 30 m thick flow, Nunatak #6.

415 (S 5.2.4.64) Basalt, Patuxent Fm., Nunatak #8, Williams Hills, Neptune Range. Moderately amygdaloidal, mostly chlorite, but some calcite. 416 (1 S.1.13.64) Basalt, Patuxent Fm., Nunatak #2, Williams Hills, Neptune Range.

417 (B4.15.1.64) Pillow basalt, Patuxent Fm., Nunatak #11, Williams Hills, Neptune Range. From interior of 30 cm. diameter pillow.

418 (10 Sa.11.1.66) Diabase, Gorecki Peak, Schmidt Hills, Neptune Range, Medium-grained. From near base of 180' thick sill intrusive into Patuxent Fm. Sill is about 100' below rhyolite flows.

419 (10 Sb.11.1.66) Diabase, 87' above sample 418. 420 (10 Sc.11.1.66) Coarse grained diabase, 13 7" above sample 418. 421 (10 Sd.11.1.66) Fine-grained diabase, 6 " below top of same sill as samples 418, 419, 420. 201 422 (B 30.1.64. BGP .11. D-3) Medium-grained diabase, Nunatak #10, Schmidt Hills, Neptune Range. From interior of 300-400* thick sill.

423 (B 30.1.64.BGP. 11.D-4) Moderately coarse-grained diabase, same locality as 422,

424 (W 66a.11.2.64) Granite gneiss, Serpan Peak, Neptune Range. Biotite (?) altered to chlorite. 425 (W 66 a a . l l . 2.64) Granite gneiss, Serpan Peak, Neptune Range. Chlorite common. 426 (W66 c . l l .2.64) Homblende-biotite-sphene gneiss, Serpan Peak, Neptune Range. Biotite partly altered to chlorite.

427 (W 66 cc.11.2.64) Homblende-biotite-sphene gneiss, Serpan Peak, Neptune Range. Biotite altered to chlorite.

428 (W 6 6 d .ll .2.64) Granite gneiss, Serpan Peak, Neptune Range.

429 (W 66e.ll.2.64) Homblende-biotite-sphene gneiss, Serpan Peak, Neptune Range. Contains a dark alteration lenticule. Biotite is chloritized. 430 (W66 f. 11.2.64A) Granite gneiss, Serpan Peak, Neptune Range. 431 (W 66 f . l l .2.64B) Granite gneiss, Serpan Peak, Neptune Range. 432 (18 S.2.12.64 R-l) Coarse-grained granite, near Serpan Peak, Neptune Range. Red variety.

433 (18 S.2.12.64W-3) Coarse-grained granite, near Serpan Peak, Neptune Range, White variety.

436 (1 Sa.2.12.65) Interbedded siltstone and slate, Patuxent Fm., Far West Peak, Patuxent Range. These samples of the Patuxent Fm. are numbered in geographic order, from North to South. 202 437 (5 S .12.4.62) Laminated slate, Patuxent Fm., Seminole Nunatak, Patuxent Range. 438 (65 S .12.11.62) Subgraywacke, Patuxent Fm., Winnebago Nunatak, Patuxent Range.

439 (9 S.2.12.65) Slate, Patuxent Fm., Pueblo Nunataks area, Patuxent Range. 440 (IS .11.30.62) (Subgraywacke, Patuxent Fm., Dash Nunatak, Patuxent Range. 441 (1 S .1 .2 4 .62a) Interbedded siltstone and slate, Patuxent Fm., Mohawk, "A" Nunatak, Patuxent Range. 442 (2XS.11.13.62) Slate, Patuxent Fm., Snowback Nunatak, Patuxent Range, 443 (95 Sb.22.12.65) Subgraywacke, Patuxent Fm., Black Pyramid, Patuxent Range. 444 (3 Sa. 11.16.62) Laminated siltstone and subgraywacke, Patuxent Fm., Comer Glacier area, Patuxent Range.

445 (S.1.2.63) Laminated siltstone, Patuxent Fm., Bannock Ridge, Patuxent Range. 446 (65F-1.31.12.62) Slate, Patuxent Fm., Ogalalla Ridge, Patuxent Range.

Thiel Mountains: Samples collected by A. B. Ford, U.S. Geological

survey, Menlo Park, California Q .S.U . No. 493 (Ford's No. 5.12.61.15) Cordierite-hypersthene quartz-monzonite porphyry, Thiel Mountains. See map of Thiel Mountains for location. 203

494 (7.12.61.1) Cordierite-hypersthene quartz-monzonite porphyry, Thiel Mtns. Slightly recrystallized, biotite rims on hypersthene. 495 (31.1.61.9) Cordierite-hypersthene quartz-monzonite porphyry, Thiel Mtns. Slightly recrystallized.

496 (10.1.62.20) Cordierite-hypersthene quartz-monzonite porphyry, Thiel Mtns. Much recrystallized, adjacent to contact with biotite granite.

497 (10.1.62.10) Biotite granite (quartz monzonite?), Thiel Mtns. Intrusive into C-H-Q porphyry. Sample is from contact zone, near #496.

498 (10.1.62.5) Biotite granite, Thiel Mtns. Same as 497, but 100 m from contact.

499 (7.12.61.4) Porphyritic quartz monzonite, Thiel Mtns. Intrusive into C-H-Q porphyry. 500 (27.12.61.8T) Biotite quartz monzonite, Thiel Mtns. Intrusive into C-H-Q porphyry. Biotite partly chloritized, plagioclase sausseritized. 501 (28.12.61.3T) Biotite quartz monzonite, Thiel Mtns. Similar to 500.

Nilsen Plateau: Samples collected by D. McLelland, made available to the author by M. J. Hibbard, University of Nevada, Reno.

O .S.U . No. 461 (McLelland's No. 77) Metavolcanic, from spur SW into Cougar Canyon, 7000' ENE of base camp, Nilsen Plateau, Queen Maud Mtns. Phenocrysts of quartz, plagioclase, and biotite set in aphanitic light gray groundmass. Hematite staining around quartz phenocrysts. 204

462 (80) Metavolcanic,' same location as 461. Similar to 461, but less numerous phenocrysts (10%).

463 (87) Metavolcanic, same location as 461. Brecciated and lacking hematite stain, but otherwise similar to 461.

464 (92) Metavolcanic, same location as 461. Shows weak foliation.

465 (131) Metavolcanic, Thermometer Ridge, east side of east branch of Cougar Canyon, Nilsen Plateau. Numerous phenocrysts (70%) of quartz, plagioclase, and biotite in gray aphanitic groundmass.

466 (132) Metavolcanic, same location as 465. 467 (137) Metavolcanic, same location as 465 and similar, but fewer phenocrysts (40%) and dark gray groundmass. 468 (143) Cougar Canyon Quartz Monzonite, (?), near location of 465, but on opposite side of a fault. Quartz phenocrysts (15%) in medium to fine-grained groundmass of K-feldspar, plagioclase, and biotite.

469 (154) Metavolcanic, South Ridge, Nilsen Plateau. Similar to 465.

470 (135) Metavolcanic, same location and similar to 465. 471 (284) Metasediment (phyllite), SW spur of Lonely Ridge. Inclusion in South Quartz Monzonite.

472 (260) Metagraywacke, south side of mouth of Black Rock Glacier, Nilsen Plateau.

473 (267) Metagraywacke, spur at head of Black Rock Glacier, Nilsen Plateau. 205 474 (271 ) M etaquartzite, south side of head of Black Rock Glacier, Nilsen Plateau.

475 (324) Metagraywacke, near location of 473.

476 (347) Metaquartzite, spur just north of Black Rock Glacier, Nilsen Plateau.

477 (49) Lonely Ridge Granodiorite, North side of Lonely Ridge, Nilsen Plateau. Medium-sized grains of plagioclase, quartz, and biotite. Shows a weak gneissic foliation. 478 (46) Lonely Ridge Granodiorite, north side of Lonely Ridge. Similar to 477. 479 (44) Lonely Ridge Granodiorite, north side of Lonely Ridge. Strong gneissic foliation, augen of plagioclase 1 cm wide.

480 (208) Lonely Ridge Granodiorite, south side of Lonely Ridge. Similar to 477, not foliated.

481 (211) Lonely Ridge Granodiorite, south side of Lonely Ridge. A "cataclastic gneiss, " foliation more pronounced than 479.

482 (215) Lonely Ridge Granodiorite, south side of Lonely Ridge. Thoroughly deformed cataclastic gneiss .

483 (216 ) Lonely Ridge Granodiorite, south side of Lonely Ridge. Similar to 482, but more intense deformation.

506 (62) South Quartz Monzonite, southwest wall of Cottonwood Canyon, Nilsen Plateau, Light gray, medium-grained, consisting mainly of quartz, K-feldspar, and plagioclase, some biotite. 206 507 (64) South Quartz Monzonite, Windy Ridge, Similar to 506, pink variety, weak gneissic foliation.

508 (94) South Quartz Monzonite, Windy Ridge. Similar to 506.

509 (103) South Quartz Monzonite, Windy Ridge. Similar to 506, but with weak gneissic foliation. 511 (148) South Quartz Monzonite (granite?), southwest of Cotton­ wood Canyon. Phenocrysts of K-feldspar (up to 1" long) in medium-grained groundmass of quartz, biotite, and plagioclase.

513 (233) South Quartz Monzonite, halfway to South Ridge. Similar to 5 06.

Coats Land O .S.U . No. 235 Rhyolite or rhyodacite, Iittlewood Nunataks, Coats Land. Small plagioclase phenocrysts (1-5 mm) in a dark-red aphanitic groundmass. Collected by N. B. Aughenbaugh and described in Aughenbaugh and others (1965). 367 Rhyolite or rhyodacite, Iittlewood Nunataks, Coats Land. Similar to 235. Collected by J.C, Behrendt.

405 (Instituto Antarctico Argentino No. CE.75 .533) Rhyolite (?), Bertrab Nunatak, Coats Land. Described as: "Graphic granite; microcline and some plagioclase grains are idiomorphic, somewhat altered to kaolin, calcite, and iron oxide. Biotite has altered to chlorite."

406 (CE.75.534) Rhyolite (?), Bertrab Nunatak, Coats Land. Similar to 405. 407 (CE.75.535) Andesite (?), Bertrab Nunatak, Coats Land. Described by Instituto Antarctico Argentino as "Micro trondjemite: quartz with undulating extinction, plagioclase (olig.-andes.), turbid because of advanced state of alteration. Abundant biotite altered to chlorite. Alotriomorphic hornblende. " 207 408 (CE.75.536) Andesite (?), Bertrab Nunatak, Coats Land. Described as "microdiorite."

409 (CE. 75.537) Rhyolite (?) Bertrab Nunatak, Coats Land. Described as "graphic granite, groundmass too fine for minerals to be determined."

Western Queen Maud Land: Samples made available by D. C. Neethling, Antarctic Division of Geological Survey, Republic South Africa.

O .S.U . No. 484 (Neethling's Lab. No. 1, Field No. U3) Basalt, Trolkjellrygg Group, Lower Member, Utkikken, W. Queen Maud Land. Very fine-grained, medium gray.

485 (Lab No. 2, Field No. SL1) Basalt, Trollkjellrygg Group, Transitional or Middle Member, Nunatak. 820. Dark gray, finegrained. 486 (Lab No. 6, Field No. SN 20) Basalt, Trollkjellrygg Group,Upper Mem., Snokallen. Similar to 485. 487 (Lab No. 9, Field No. SJ11) Basalt, Trollkjellrygg Group, Upper Mem., Snokjerringa, Similar to 485. 488 (Lab No. 10, Field No. SJ22) Basalt, Trollkjellrygg Group, Upper Mem., Snokjerringa. Similar to 485. 489 (Lab No. 12, Field No. B8) Basalt, Trollkjellrygg Group, Upper Mem., Bolten. Dark red-brown, small phenocrysts of olivine and pyroxene. 490 (Lab No. 16, Field No. SN5) Basalt, Trollkjellrygg Group, Upper Mem., Snokallen. Similar to 485.

491 (Lab No. 17, Field No. SN39) Basalt, Trollkjellrygg Group, Upper Mem., small Nunatak southeast of Snokallen. Similar to 489. 492 (Lab No. 19, Field No. SN6) Basalt, Trollkjellrygg Group, Upper Mem., Snokallen. Similar to 485. BIBLIOGRAPHY

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