Precambrian Geology of the North Mawson Escarpment Area, Prince Charles Mountains, Antarctica

Precambrian geology of the North Mawson Escarpment area, Prince Charles Mountains, Antarctica

Adrian F. Corvino

Submitted in total fulﬁlment of the requirements of the degree of Doctor of Philosophy

May 2009

School of Earth Sciences The University of Melbourne ii Declaration

This is to certify that

(i) the thesis comprises only my original work towards the PhD;

(ii) due acknowledgement has been made in the text to all other material used, and;

(iii) the thesis is less than 100,000 words in length, exclusive of tables, maps, bibliogra- phies and appendices.

Signed,

Adrian F. Corvino

iii iv “In the exploration of a continent the mountainous areas are generally the last strongholds of mystery...”

— Eric Shipton

v vi Abstract

Part of East Antarctica’s shield collided with Greater India during assembly of the Rodinia supercontinent, causing these landmasses to become welded together by about 900 million years ago. The pre-Rodinia continental margin of the Antarctic landmass is represented by the North Mawson Escarpment area of Antarctica’s Prince Charles Mountains. The size of this postulated Antarctic landmass is still unknown, though it might make up a considerably vast segment of the presently subglacial East Antarctic shield. Only with the assembly of Gondwana about 500 million years ago was the entire shield fully consolidated. The above conclusion is supported by the ﬁndings presented in this thesis, which is the ﬁrst detailed examination of the Precambrian geology of the North Mawson Escarpment area incorporating the Lawrence Hills and Clemence Massif. The North Mawson Escarpment, 72◦30’–73◦10’S, 68◦E, consists of grey gneisses of granitic to granodioritic composition, including adamellitic augen-gneiss types, and metasupracrustal successions; the latter contain multilayered calcsilicate gneiss, metacarbonate, metapelitic gneiss and schist, quartzite and amphibolite. Radiometric dating results presented in this work demonstrate conclusively that the grey gneisses are of Palaeoproterozoic age. These grey gneisses originated from large magmatic bodies that were episodically emplaced and crystallised in the period 2490–2420 Ma. Other granitic protoliths, of lesser volume, were emplaced in the interval 2180–2080 Ma at which time the older types were at least thermally overprinted if not substantially deformed. The exact age and origin of the metasupracrustal rocks is unknown, though their precursors were for the most part laid down after 2450 Ma and before 900 Ma. They are interpreted as having been deposited during periods of tectonic extension operating throughout the Mesoproterozoic in a pas- sive margin setting; that is, on the converging Antarctic landmass prior to its collision with India in Rodinia times. Bordering directly on the northern margin of the escarpment are the low-lying Lawrence Hills, 72◦30’S, 68◦43’E, where Palaeoproterozoic and Late Mesoproterozoic crustal components are juxtaposed. Further north at Clemence Massif, 72◦12’S, 68◦40’E, only high-

vii grade metamorphic rocks of Late Mesoproterozoic age are exposed. Thus, a southward progression from Late Mesoproterozoic to Palaeoproterozoic to Archaean crust is clearly recognised for over 100 km along the study area. Having examined the structure, it is my conclusion that the rock masses were stacked by oblique northward overthrusting motions while they were deforming pervasively in the infrastructure zone of a convergent orogen, i.e. when this part of pre-Rodinia Antarctica collided with India. The older over-riding Palaeoproterozoic basement of the North Mawson Escarpment was at this time exhumed to shallower, but still deep crustal levels, resulting in a Barrovian-type metamorphism that evolved to high–T, low–P conditions. This transitional amphibolite to granulite facies regional metamorphism outlasted most of the ductile deformation with temperatures reaching 750◦C, though potentially greater, under pressure conditions of about 5 kbar. Whereas, the underthrust Late Mesoproterozoic rocks of Clemence Massif were meta- morphosed to even higher granulite facies temperatures followed by an isobaric cooling history. It is also found that the areas dominated by Late Mesoproterozoic crust, i.e. from Lawrence Hills northward, correspond closely to a prominent series of linear NE–SW trending positive magnetic anomalies. Such anomalies do not appear across the North Mawson Escarpment, though these older rocks nevertheless share the same trend in their basement structure. There is little doubt that the trend of the magnetic anomalies is directly related to the deformation that produced the Rayner belt, which is the zone of collision between the aforementioned Indian and Antarctic landmasses. It is my contention that the Late Mesoproterozoic crust and the magnetic anomalies correlate with arc-related crustal additions originally formed in a convergent margin setting leading up to this collision; that is, they lie within the intensely deformed orogen interior rather than on the continental basement southward. Structural and metamorphic interference between the Rayner belt and the younger Gondwanan Prydz belt, which is more NW–SE trending, becomes increasingly important southward of the study area. Much work still needs to be done to correctly determine the overprinting relationships between these two high-grade belts, a problem that is most likely to be resolved by more targeted analyses of rocks from where the North and South Mawson Escarpment overlap.

viii ix x Acknowledgements

First and foremost I thank Prof. Chris Wilson for his patience and help in supervising my research, and for granting me the greatest undertaking of my life to work in Antarctica. Secondly, I thank Steve Boger for sharing the fieldwork and providing endless hours of discussion on the geology of the Prince Charles Mountains, especially the Mawson Es- carpment. As far as I know, he remains the only person who has seen and traversed the entire length of this escarpment by foot! I owe a debt of gratitude to many other people. In no particular order, Glen Phillips and Mark McLean for their mateship, and who shared the journey of Ph.D. research on Antarctic geology; Friedhelm Henjes-Kunst for his collaboration on rock samples from the Lawrence Hills and Rofe Glacier; Ian Fitzsimons for his assistance with the U–Pb zircon dating and accommodating me on visits to Perth; Bill Baxter and Gary Kuehn for their invaluable field guidance; Richard White for his assistance with the computer program Thermocalc; Liaxi Tong and Cameron Quinn for discussions on the geology of the Prydz Bay area, and Jacqueline Halpin on the Stillwell Hills; Daniel Viete for the opportunity to assist with his fieldwork on the classic Barrovian series rocks in Scotland; Mark Quigley for the opportunity to collaborate on his rock samples from Tibet; Gordon Holm and Graham Hutchinson for their help with the thin section preparations and electron microprobe work, and; Richard Stanaway for lending his oblique aerial photos of the Mawson Escarpment. I thank them all for their friendship. I am also grateful to Ed Grew, Wilfred Bauer, Chris Carson, Geoff Clarke, Eugene Mikhalsky and Nigel Kelly for critically reviewing particular chapters published in the course of putting this thesis together. Special thanks to Ron Vernon and Ed Grew for their very generous thesis reviews. Thanks to Mum, Dennis, Kris, Jess and Dad for all their encouragement over the last six years. Lastly and most of all I thank Angela for her love and undying support of my endeavours. This thesis was compiled using the typesetting system LATEX 2ε. All errors are my own.

xi xii Contents

Abstract...... vii Acknowledgements ...... xi Abbreviations...... xxiii Mineralsymbols ...... xxv

I Background Information 1

1 Introduction 3 1.1 Scientiﬁc relevance—understanding East Antarctica ...... 4 1.2 Exploration in the Prince Charles Mountains ...... 7 1.3 Fieldwork ...... 8 1.4 Thesis overview and publications ...... 8

2 Physical geography 13

3 Tectonic subdivisions of the Prince Charles Mountains 17

II Clemence Massif and Lawrence Hills 21

4 General geology of Clemence Massif 23 4.1 Summary ...... 23 4.2 Introduction...... 24 4.3 Field relationships and petrography ...... 27 4.4 Structure ...... 31 4.5 U–Pbzircondating...... 35 4.6 Discussion...... 41 4.7 Concludingremarks ...... 46

xiii 5 Metamorphism of a Clemence Massif metapelite 47 5.1 Summary ...... 47 5.2 Introduction...... 48 5.3 Petrography and mineral chemistry ...... 48 5.4 Bulkchemicalcomposition...... 52 5.5 Pseudosectionmodelling ...... 55 5.6 Temperature estimates using geothermometers ...... 59 5.7 Discussion...... 59

6 2.5 and 1.1 billion year old crust in Lawrence Hills 63 6.1 Summary ...... 63 6.2 Introduction...... 64 6.3 Localgeologicsetting ...... 65 6.4 Sample descriptions, geochemistry and radiometric dating results ...... 67 6.5 Evidence for Early Palaeoproterozoic crustal development ...... 80 6.6 Evidence for Late Mesoproterozoic crustal development ...... 84 6.7 Timing of reworking and juxtaposition of crustal components ...... 84 6.8 Signiﬁcance of the Neoarchaean ages ...... 85 6.9 Origin of the high magnetic anomaly ...... 86

III North Mawson Escarpment 89

7 Lithodemic Units 91 7.1 Introduction...... 91 7.2 Lithodemicsubdivisions ...... 91 7.3 Field and petrographic descriptions ...... 92 7.4 Lategranites ...... 118 7.5 Closingremarks...... 119

8 Superimposed events at 2450 Ma, 2100 Ma, 900 Ma and 500 Ma 123 8.1 Summary ...... 123 8.2 Introduction...... 124 8.3 Previousradiometricdating ...... 125 8.4 Sampleselection ...... 128 8.5 Sample descriptions and U–Pb zircon dating ...... 131 8.6 Interpretationofresults ...... 147

xiv 8.7 Regionalimplications...... 151 8.8 Conclusions ...... 155

9 Structure and tectonic evolution 157 9.1 Introduction...... 157 9.2 Structural subareas and deformation histories ...... 158 9.3 Large-scale development history of structural subareas...... 182 9.4 General description of microstructures and metamorphism...... 185 9.5 Key microstructures in metapelites ...... 186 9.6 Physical conditions of metamorphism ...... 190 9.7 Radiometric age constraints on the deformation history ...... 193 9.8 Tectonic interpretation with emphasis on the Rayner belt ...... 196

References 205

A Analytical methods 237 A.1 ChemicalandSm–Ndanalyses ...... 237 A.2 Zircon separation and SHRIMP ion-microprobe U–Pb analysis ...... 238

B Mineral chemistry of some maﬁc rocks 241

C Chemical analyses of augen-gneiss 247

D Chemical analysis of an amphibolite dyke 251

E Chemical analyses of metapelites 253

F Microprobe analyses of minerals in metapelites 255

G P–T Pseudosection for Barkell Platform metapelite 265

xv xvi List of Figures

1.1 Map of the Prince Charles Mountains...... 6 1.2 Field camp in the Waller Hills, North Mawson Escarpment...... 9 1.3 Fieldwork in the North Mawson Escarpment...... 10

2.1 Oblique aerial photographs of the Mawson Escarpment ...... 14

◦ 3.1 Map of tectonic subdivisions recognised in the East Antarctic sector between long. 45 and 80◦E ...... 18

4.1 Oblique aerial photograph of Clemence Massif...... 25 4.2 Simpliﬁed geologic map of Clemence Massif ...... 26 4.3 Field photograph of magnetite-bearing felsic orthogneiss at Clemence Massif ...... 29 4.4 Field photograph of macroscopic layering in metasupracrustal rocks at Clemence Massif . 31 4.5 Photomicrographs of granoblastic quartz–feldspar microstructures in Clemence Massif rocks...... 32 4.6 Photomicrographs of microstructure in maﬁc and felsic layers in two-pyroxene gneiss from Clemence Massif...... 33 4.7 Orientation data for Clemence Massif...... 34 4.8 Field photograph of early layer-parallel shear structure at Clemence Massif...... 35 4.9 Field photograph of late folds at Clemence Massif ...... 36 4.10 Concordia plot of U–Pb zircon analyses for magnetite-bearing felsic orthogneiss from Clemence Massif...... 37 4.11 Concordia plot of U–Pb zircon analyses for leucogneiss from Clemence Massif...... 41 4.12 Concordia plot of U–Pb zircon analyses for crosscutting pegmatite dyke from Clemence Massif...... 42

5.1 Clemence Massif metapelite...... 50 5.2 Photomicrographs of mineral relationships in Clemence Massif metapelite...... 51

xvii 5.3 P–T pseudosection in MnNCKFMASHTO for Clemence Massif metapelite...... 58

5.4 P–T pseudosection for Clemence Massif metapelite contoured for XFe of garnet and biotite. 59 5.5 P–T pseudosections for Clemence Massif metapelite contoured for mineral proportions. . 60

5.6 T–XEBC pseudosection for Clemence Massif metapelite...... 61

6.1 Oblique aerial photograph of the Lawrence Hills...... 65 6.2 Field and aerial photographs of the study sites at Lawrence Hills...... 68 6.3 Photomicrographs of Lawrence Hills rocks...... 75

6.4 Zr/TiO2 vs. Nb/Y diagram for Lawrence Hills rocks...... 76 6.5 Normalised trace element abundance diagrams for Lawrence Hills rocks...... 77 6.6 Concordia plot of U–Pb zircon analyses for metapsammitic gneiss from Lawrence Hills. . 78 6.7 Concordia plot of U–Pb zircon analyses for Mesoproterozoic leucocratic gneiss from Lawrence Hills...... 78 6.8 Concordia plot of U–Pb zircon analyses for Palaeoproterozoic leucocratic gneiss from Lawrence Hills...... 81

7.1 Series of maps showing the distribution of lithodemic units along the North Mawson Escarpment...... 93 7.2 Field photographs of granitic grey gneiss in the Waller Hills, North Mawson Escarpment. 94 7.3 Field photograph of metasupracrustal rocks intruded by leucogranites in Lines Ridge. . . 99 7.4 Field photograph of meta-ultramafic lens enclosed by migmatitic-leucocratic-biotite gneiss in the Rofe Glacier area...... 102 7.5 Field photograph of migmatitic-leucocratic-biotite gneiss in the Rofe Glacier area. . . . . 103 7.6 Field photograph of layered grey gneiss crosscut by pegmatitic leucogranite bodies in the Rofe Glacier area...... 104 7.7 Field photograph of grey gneiss crosscut by swarm of pegmatite dykes in the Rofe Glacier area...... 105 7.8 Photomicrograph of calcic amphibole replacing clinopyroxene in grey gneiss from the Rofe Glacier area...... 106 7.9 Photomicrograph of spinel-pyroxene-hornblende meta-ultramafic rock from the Rofe Glacier area...... 106 7.10 Photomicrograph of rare symplectite-like intergrowth between cordierite and quartz in a metapelitic schist from near Petkovic Glacier...... 107 7.11 Field photographs of augen-gneiss and pegmatite in Sulzberger Bluff...... 110 7.12 Field photographs of grey gneiss in Harbour Bluff...... 112 7.13 Plagioclase-phyric amphibolite from Harbour Bluff...... 113

xviii 7.14 Photomicrograph of garnet porphyroblast in amphibolite from near Manning Glacier. . . 114 7.15 Oblique aerial photograph of the southern end of Harbour Bluff...... 116 7.16 Close-up photograph of garnet-bearing cummingtonite schist in Harbour Bluff...... 118 7.17 Crosscutting aplitic granite dyke in Harbour Bluff...... 120

8.1 Simplified geological map of the North Mawson Escarpment...... 126 8.2 Field photograph of granite dykes crosscutting migmatitic paragneiss in the Waller Hills. 128 8.3 Field photographs of rock samples in the North Mawson Escarpment dated by U–Pb zircon analyses...... 129 8.4 Cathodoluminescence images of some investigated zircons...... 130 8.5 Concordia plots of U–Pb zircon analyses for granite dykes from Waller Hills...... 139 8.6 Concordia plots of U–Pb zircon analyses for grey gneiss and interboudin leucosome from Waller Hills...... 140 8.7 Concordia plots of U–Pb zircon analyses for leucosome material and amphibolite from the Rofe Glacier area...... 141 8.8 Concordia plots of U–Pb zircon analyses for metapelitic schist and augen-gneiss from Sulzberger Bluff...... 142 8.9 Concordia plot of U–Pb zircon analyses for pegmatitic granite from Harbour Bluff. . . . 143 8.10 Histograms of all zircon ages for the North Mawson Escarpment...... 148 8.11 Distribution of zircon ages vs. latitude along the Mawson Escarpment...... 152

9.1 Map of structural subareas areas in the North Mawson Escarpment...... 159 9.2 Cross section through the North Mawson Escarpment...... 160 9.3 Schematic block diagram of large-scale fold structure in the North Mawson Escarpment. . 161 9.4 Orientation data for structural subareas of the North Mawson Escarpment...... 162 9.5 Field photograph of large-scale isoclinal synform in Lines Ridge...... 165 9.6 Field photographs of structures in Lines Ridge and Barkell Platform...... 166 9.7 Sketches of fold profiles in the North Mawson Escarpment...... 167 9.8 Schematic cross sections for parts of the North Mawson Escarpment...... 169 9.9 Orientation data for transpressive-phase structures between Barkell Platform and Rofe Glacier...... 170 9.10 Field photographs of structures between Barkell Platform and Rofe Glacier...... 173 9.11 Field photographs of structures in Waller Hills...... 174 9.12 Field photographs of structures in the Rofe Glacier area...... 175 9.13 Field photographs of structures between Petkovic Glacier and Harbour Bluff...... 178 9.14 Fold geometry and orientation of grey gneiss in Harbour Bluff...... 181

xix 9.15 Photomicrographs of Harbour Bluff rocks...... 183 9.16 Photomicrographs of granoblastic microstructure in North Mawson Escarpment rocks. . . 187 9.17 Photomicrographs of key microstructures in metapelites from the North Mawson Escarp- ment...... 191 9.18 Sketch of garnet-bearing leucosome in metapelite from Sulzberger Bluff...... 192 9.19 P–T pseudosections in MnNCKFMASHTO for a Sulzberger Bluff metapelite...... 194 9.20 Schematic model depicting the formation of the Rayner belt in Rodinia assembly . . . . 198

C.1 Primitive mantle normalised abundance diagram for augen-gneiss from the Helmore Glacier area...... 249

D.1 Primitive mantle normalised abundance diagram for an amphibolite dyke from Harbour Bluﬀ...... 252

E.1 AFM projection of metapelite bulk compositions and phase relations...... 254

G.1 P–T pseudosection in MnNCKFMASHTO for Barkell Platform metapelite...... 266

xx List of Tables

4.1 Petrography of rocks samples from Clemence Massif...... 28 4.2 SHRIMP U–Th–Pb zircon data for a pegmatitic granite dyke from Clemence Massif. . . 38 4.3 SHRIMP U–Th–Pb zircon data for leucogneiss and magnetite-bearing felsic orthogneiss from Clemence Massif...... 39

5.1 Petrographic data for Clemence Massif metapelite...... 52 5.2 Listing of minerals properties...... 53 5.3 Representative electron microprobe analyses of garnet and biotite in Clemence Massif metapelite...... 54 5.4 Representative electron microprobe analyses of K-feldspar, ilmenite, rutile and spinel in Clemence Massif metapelite...... 55 5.5 Bulk composition of Clemence Massif metapelite...... 56

6.1 Petrographic data for Lawrence Hills rocks...... 67 6.2 Whole-rock chemical analyses for Lawrence Hills rocks...... 71 6.3 Sm–Nd isotopic analyses of Lawrence Hills rocks...... 72 6.4 SHRIMP U–Th–Pb zircon data for metapsammitic gneiss and Mesoproterozoic leucocratic gneiss from Lawrence Hills...... 73 6.5 SHRIMP U–Th–Pb zircon data for Palaeoproterozoic leucocratic gneiss from Lawrence Hills...... 74

7.1 Petrographic data for rocks from Lines Ridge...... 97 7.2 Petrographic data for rocks from Barkell Platform and Waller Hills...... 98 7.3 Petrographic data for rocks from the Rofe Glacier area...... 101 7.4 Petrographic data for rocks from Sulzberger Bluﬀ...... 111 7.5 Petrographic data for rocks from Harbour Bluﬀ...... 117

8.1 Summary of U–Pb zircon ages and events in the North Mawson Escarpment...... 127

xxi 8.2 SHRIMP U–Th–Pb zircon data from Waller Hills...... 134 8.3 SHRIMP U–Pb zircon data from Waller Hills (continued)...... 135 8.4 SHRIMP U–Th–Pb zircon data from the Rofe Glacier area...... 136 8.5 SHRIMP U–Th–Pb zircon data from Sulzberger Bluﬀ...... 137 8.6 SHRIMP U–Th–Pb zircon data for pegmatitic granite dyke from Harbour Bluﬀ. . . . . 138

9.1 Structural trends in the North Mawson Escarpment...... 163

B.1 Chemical analyses of pyroxene and biotite in two-pyroxene gneiss from Clemence Massif. 242 B.2 Chemical analyses of ilmenite and feldspar in two-pyroxene gneiss from Clemence Massif. 243 B.3 Chemical analyses of amphiboles in rocks from the Rofe Glacier area...... 244 B.4 Chemical analyses of pyroxene, biotite and spinel in maﬁc and meta-ultramaﬁc rocks from the Rofe Glacier area...... 245

C.1 Chemical analyses of augen-gneiss from the Helmore Glacier area...... 248

D.1 Chemical analysis of an amphibolite dyke from Harbour Bluﬀ...... 251

E.1 Bulk compositions of North Mawson Escarpment metapelites...... 253

F.1 Analyses of garnets in metapelites from the North Mawson Escarpment...... 256 F.2 Analyses of garnets in metapelites from the North Mawson Escarpment (continued). . . 257 F.3 Analyses of cordierites in metapelites from the North Mawson Escarpment...... 258 F.4 Analyses of biotites in metapelites from the North Mawson Escarpment...... 259 F.5 Analyses of feldspars in metapelites from the North Mawson Escarpment...... 260 F.6 Analyses of feldspars in metapelites from the North Mawson Escarpment cont...... 261 F.7 Analyses of ilmenites and spinels in metapelites from the North Mawson Escarpment. . . 262 F.8 Analyses of staurolites in metapelites from the North Mawson Escarpment...... 263

xxii Abbreviations

amu atomic mass units apfu atoms per formula unit ◦C degreescelsius Ga Giga annum, billions of years before present kbar kilobars µm micron,10−6 m Ma Mega annum, millions of years before present MSWD Mean Square of Weighted Deviates m.y. millions of years P pressure T temperature

xxiii xxiv Mineral symbols

act actinolite ksp K-feldspar aln allanite mic microcline ap apatite mnz monazite bi biotite mt magnetite ca-amph calcic amphibole mu muscovite cc calcite opx orthopyroxene chl chlorite phl phlogopite crd cordierite pl plagioclase cz clinozoisite q quartz cpx clinopyroxene ser sericite cumm cummingtonite scp scapolite en enstatite sill sillimanite ep epidote sp spinel fs ferrosilite sph sphene (titanite) g garnet st staurolite grun grunerite tr tremolite hbl hornblende ts tschermakite herc hercynite wo wollastonite ilm ilmenite zrc zircon

xxv Part I

Background Information

Chapter 1

Introduction

“In the exploration of a continent the mountainous areas are generally the last strongholds of mystery to fall before the onslaught of man, be that onslaught brutal, scientiﬁc or merely inquisitive”. These words, written by mountaineer and explorer Eric Shipton in his book Nanda Devi, are as relevant now to Antarctica’s Prince Charles Mountains as they were to India’s Himalaya when he wrote them in 1936. Although far from being as elevated as the Himalaya, the Prince Charles Mountains are nevertheless just as remote and inaccessible, and they have remained even less explored. Unlike the Himalaya, which owe their origin to colliding tectonic plates, these Antarctic mountains are situated along an intracontinental rift margin and were uplifted due to tectonic extension. However, the Precambrian rocks of which they are composed have been reshaped by several Himalayan- style mountain building events over the course of a long history spanning back to Archaean times. Preserved in their structure, for example, is the evidence of processes operating in East Antarctica’s deep continental crust during two of the world’s largest orogenies in which the supercontinents Rodinia and Gondwana were made and unmade (Rino et al., 2008). In the most recent theory, these orogenies are described in East Antarctica by modern-type Wilson Cycle processes of alternating ocean opening and closing, continental break up and continental collision (Mikhalsky, 2008). This is arguably an important model to be considered for East Antarctica’s continental evolution since at least 2.5 billion years ago, though the theory remains to be proven. It is the Precambrian history of the rocks and their reshaping during such orogenies that is the underlying subject of this thesis. The work is focussed on the North Mawson Escarpment area in Antarctica’s Prince Charles Mountains.

3 Introduction

1.1 Scientiﬁc relevance—understanding East Antarctica

In the simplest interpretation, the Antarctic sector between 45◦ and 80◦E consists of three Archaean and Palaeoproterozoic cratonic blocks separated by the Rayner orogen, which forms a continuous belt between them. The cratonic blocks, which had stabilised by 1600 m.y. ago, are represented by the Vestfold Hills in Princess Elizabeth Land, the Napier Complex in Enderby Land and the Ruker Complex of the Southern Prince Charles Mountains in MacRobertson Land (e.g. Harley, 2003). The Rayner belt marks a collision zone where Late Mesoproterozoic accretionary complexes and arc-related igneous rocks were compressed and deformed by converging continental landmasses about 1000 to 900 m.y. ago. The regional spatial relationships between the cratonic blocks and their marginally reworked zones, which lie adjacent to progressively younger accreted terranes and synorogenic granitic plutons within the collisional belt, is characteristic of ocean- driven plate mechanisms. Considered in a plate tectonic model, most of the Rayner belt represents the buoyant continental crust that was not destroyed by plate consumption, whereas most oceanic lithosphere was probably consumed. Evidence of such oceanic crust, if it existed, is potentially preserved in the Fisher Complex of Antarctica’s Prince Charles Mountains (Mikhalsky et al., 1996, 1999; Mikhalsky, 2008). The Rayner belt was produced when Greater India collided with part of East Antarc- tica’s shield. This happened late in the assembly of the Rodinia supercontinent that is recorded by worldwide orogenic events from 1300 until about 900 m.y. ago (Li et al, 2008). On this reconstruction, East Antarctica was likely to have been connected to a landmass including Laurentia, Australia and India, all welded together along a series of mountain belts (Moores, 1991; Dalziel, 1991; Hoffmann, 1991). By around 750 m.y. ago, however, Rodinia had begun to breakup and was no longer a coherent landmass; Australian and Indian landmasses were separated, though each now contained fragments of East Antarc- tica (Torsvik, 2003). These Antarctic fragments were reassembled by a series of orogenic events, mainly lasting from 650 until 500 Ma, leading to formation of the Gondwana supercontinent. The greater landmasses of South America–Africa and East Antarctica– India–Australia, and their constituent cratonic parts, were all brought together at this time. The position and nature of any Gondwanan sutures in the East Antarctic shield are, however, still difficult to define. In Antarctica’s Princess Elizabeth Land, a major zone of granulite facies metamorphism referred to as the Prydz belt is one possibility. This belt, which has variably overprinted the Rayner belt and the cratonic blocks it separates,

4 Introduction is clearly recognised as a feature related to Gondwana assembly. A leading problem is whether it represents the site of collision between the pre-Gondwanan Antarctica–Australia and Antarctica–India continents. Geological studies on this belt in the Prydz Bay area over the last 15 years has helped bring about a paradigm shift concerning the way in which East Antarctica’s shield was pieced together in Rodinia and Gondwana times. The modern thinking, which suggests parts of East Antarctica were fragmented prior to Gondwana assembly, requires that a suture zone must now exist between them somewhere. The Prydz belt could represent this feature, but the geodynamic processes that brought about its evolution remain unresolved. For example, unlike the Rayner belt, there are no large volumes of relatively juvenile arc-related materials indicating an active plate margin, or any geophysical information telling of an orogen-scale structure. Thus, the Prydz belt itself is probably not a suture zone formed by continental collisions, though it is very likely to be the intracratonic consequence of such processes operating elsewhere (Wilson et al., 2007; Mikhalsky, 2008). So far, the most defensible but still conjectural case for a suture is that it lies in the Southern Prince Charles Mountains where isotopic geochronology work indicates that juxtaposed Archaean and Palaeoproterozoic blocks may have evolved separately before 500 Ma (Boger et al., 2001, 2008). Large volumes of 500 m.y. old charnokites in the Grove Mountains might be another indicator of granite genesis related to an orogenic belt situated further inland. The major objective of this thesis is to help ﬁll some of the remaining gaps in the continental evolution of East Antarctica by examining the little studied North Mawson Escarpment area in the Prince Charles Mountains. This area is seen as a pivotal piece in the jigsaw puzzle of East Antarctica’s assembly because it exposes parts of an Archaean cratonic core and accreted Palaeoproterozoic crust which was progressively stabilised and remobilised during both the Rayner and Prydz events. The results provided in this thesis are therefore relevant in testing Rodinia and Gondwana reconstructions. One outstand- ing problem is to determine the size of the Antarctic fragment that was already welded to India before Gondwana assembly. Another is the unknown nature of the subglacial Gamburtsev Mountains that lie a further 800 km inland from the study area. Prelimi- nary ﬁndings of geophysical investigations conducted in the 2007–2009 International Polar Year are revealing that these mountains have a ruggedness and size typical of a younger Phanerozoic orogen, such as the European Alps. The mechanism of their formation, once it is understood, will undoubtedly be more meaningful if it can be placed in the context of a working hypothesis for the Prince Charles Mountains.

5 Introduction

70° Athos Range

a l

u e s ng n Porthos Ra i n e ge P y n t a t R e is J m ra A 71°

Mt Meredith

Mt Collins Prince Charles Fisher Massif Mountains Mt Willing Nilsson Rocks

Shaw Massif 72°

r Clemence 50 km Mt Izabelle e Massif i

c (Ch. 4,5)

l Lawrence G Mt Johns Hills (Ch.6) North Mawson Mt Cresswell Escarpment (Ch. 7–9)

Mt Rymill

Mt McCauley 73°

t r

Goodspeed Mt Stinear e Law Nunataks Fisher Glacier b

Mt Rubin m Plateau

a L

Mt Menzies Mt Ruker Cumpston Massif Keyser Ridge Mt Newton Mellor Glacier Mt Maguire 74° Blake Nunataks Mt Twigg Wilson Bluff

60° 62° 64° 66° 68° 70°

Figure 1.1. Map of the Prince Charles Mountains showing the areas investigated. Komsomolsky peak, ◦ ◦ 75 45’S, 63 25’E, is not shown.

6 Introduction

1.2 Exploration in the Prince Charles Mountains

The Prince Charles Mountains, first sighted in 1946–47, form some of the largest rock exposures of the East Antarctic shield (Fig. 1.1). These mountains, rising to altitudes of up to 3300 m though generally less than 2500 m, are predominantly situated between latitudes 70◦10’S and 75◦45’S, and longitudes 60◦40’E and 69◦00’E, where they flank the Lambert Glacier and its underlying rift. They are of special interest to Antarctic geology because, along with the Grove Mountains to their east, they are the only major outcrops to appear substantially inland from the continental margin; the most southern exposure is Komsomolsky peak, 75◦45’S, 63◦25’E, about 800 km into the Antarctic interior. Exploration in the Prince Charles Mountains has been undertaken by Australian and Russian workers since the 1950’s with the largest reconnaissance expeditions conducted in the early 1970’s. Since then, smaller investigations in the northern half of the mountains have continued sporadically up to the present day. However, owing to their remoteness, access to the mountain ranges lying deeper south, beyond lat. 72◦S, has been far more limited. Following their last major survey in 1974, these southern mountains were not revisited again for more than 20 years until small trips were made to a few specific localities in 1987–90 and 1998–99. The largest field program in the Southern Prince Charles Mountains was conducted in the 2002–03 season, when 35 expeditioners, including 14 geologists, were supported by Twin Otter aircraft and two squirrel helicopters operating from a base camp near Mount Cresswell. This program, known as the Prince Charles Mountains Expedition of Germany and Australia, included a major airborne geophysical survey as well as detailed field investigations of all of the significant rock outcrops. The group of scientific personnel were under the direction of Prof. Chris Wilson and Dr. Norbert Roland, including investiga- tors from five Australian, one Russian and six German research institutions. A general account of the work of this expedition can be found in the preface of Terra Antartica, vol. 12, 2005. Results have been presented in a number of scientific papers, the most influential ones by Mikhalsky et al. (2006a), Phillips et al. (2006, 2007a, b), McLean et al. (2008), Corvino et al. (2008) and Phillips and Läufer (2009). These papers, along with others by Boger et al., (2001, 2006, 2008), Boger and Wilson (2003, 2005), Reading (2006), Veevers et al. (2008) and Veevers and Saeed (2008), have helped establish a more complete understanding of the evolution of Southern Prince Charles Mountains. As Adie (1962) pointed out, it is inevitable in the exploration of any continent the size of Antarctica that geological survey must follow the course of reconnaissance mapping

7 Introduction followed by various degrees of more detailed survey. It is only within the last five to ten years that it can be said that the next stage of a more detailed study of the Southern Prince Charles Mountains has commenced in earnest, of which this thesis is one contribution. The findings of almost all previous geoscientific endeavours, i.e. those carried out over the second half of last century, can be found in the bulletin by Mikhalsky et al. (2001a) and references therein.

1.3 Fieldwork

The results and interpretations presented in this thesis are based on geological fieldwork carried out as part of the 2002–03 Prince Charles Mountains Expedition of Germany and Australia. Rocks along the North Mawson Escarpment were investigated during a six week period, from 16 January 2003 to 7 December 2002, by myself and Steve Boger. A traverse of the west-facing cliffs from Lines Ridge to Harbour Bluff was conducted, basing our activities out of a series of small camps established along the way (Figs. 1.2, 7.3 and 7.6). About half of the time was spent in companionship with field guides Bill Baxter and Gary Kuehn, and a few days in the Waller Hills and Rofe Glacier area with Prof. Chris Wilson. A total of 147 rock samples were collected. On 17 January 2003, Boger, Baxter and I were relocated to Clemence Massif and spent the next five days working mainly along its eastern side. A small base camp was established on a prominent flat-lying area, at lat. 72◦13’07”S and long. 68◦48’30”E. Brief excursions were made to the north end and west side of the massif by helicopter on 21 January 2003 before departure to Mount Cresswell ending the scientific expedition. A further 11 samples were collected from Clemence Massif. No visits were made into the Lawrence Hills, though rock samples from that area were kindly provided by Friedhelm Henjes-Kunst. These are examined in Chapter 6.

1.4 Thesis overview and publications

This thesis is divided into three parts. The ﬁrst part is made up of three short chapters that deal with the introductory and background material; short reviews of the physical geography and regional geology are provided. The second part, chapters 4–6, includes work on the Clemence Massif and Lawrence Hills (Fig. 1.1). Chapter 4 describes the main geological relationships of Clemence Massif and presents new radiometric age de- terminations for three rocks. Following this, Chapter 5 gives a more detailed study on

8 Introduction

Figure 1.2. Field camp in the Waller Hills, North Mawson Escarpment, 20 December 2002.

the metamorphic evolution of the massif founded on the petrography and petrology of a metapelitic sillimanite–garnet gneiss. Chapter 6 presents Sm–Nd and U–Pb chronology data for continental crust formation in the Lawrence Hills, which lie south of Clemence Massif bordering the North Mawson Escarpment (Fig. 1.1). On this area, a collaboration was undertaken with Friedhelm Henjes-Kunst, who provided the results and descriptions relating to the chemical and Sm–Nd analyses. The findings show that these hills coin- cide with a major boundary between Late Mesoproterozoic rocks, corresponding to those at Clemence Massif, and the Palaeoproterozoic crust that dominates the North Mawson Escarpment further south. The final part, including chapters 7–9, is the major study on the North Mawson Es- carpment (Fig. 1.1). It opens with Chapter 7 that describes the field and petrographic aspects of the rock types, which, in order to facilitate the large-scale tectonic interpretation, are grouped into several major lithodemic units. Fundamentally, the work of this chapter may be likened to the stage of collating the pieces of a jigsaw puzzle before they are assembled into a more detailed picture. Chapters 8 and 9 present the results of more detailed studies on these rocks, dealing with their isotopic geochronology, structure and

9 Introduction

Figure 1.3. Fieldwork high up on the North Mawson Escarpment. Looking at pegmatite from left to right are Prof. Chris Wilson, Steve Boger and Bill Baxter. The rocks are at altitudes of 800–1000 m, about 600 m higher than the Lambert Glacier below. In the background Cumpston Massif and Mt. Rubin can be seen on the far left and middle right, over 100 km away to the south and southwest respectively. On the far right is Mt. Stinear approximately 50 km to the west-southwest.

tectonic evolution. The discussions in these chapters draw together some of the earlier work of the thesis into a more coherent account of the tectonic evolution. A study of the metamorphic petrology of the escarpment is ongoing; some of the preliminary work is provided in Chapter 9. For the interested reader, much of the raw petrological data can be found in the appendicies. Several of the chapters have been published during the course of writing this thesis. They have been variably modified in this work to keep up with the research findings made after their original publication, though essentially are the same. The following is a list of the papers, either published or submitted, related directly to this research and other relevant scientific collaborations. Copies of these are included separately at the back of the thesis.

Corvino, A.F., in press. Photograph of the Month: Flanking folds and boudins in the Prince Charles Mountains. Journal of Structural Geology, doi:10.1016/j.jsg.2008.01.014

10 Introduction

Corvino, A.F., Boger, S.D., Henjes-Kunst, F., Wilson, C.J.L., Fitzsimons, I.C.W., 2008. Su- perimposed tectonic events at 2450 Ma, 2100 Ma, 900 Ma and 500 Ma in the North Mawson Escarpment, Antarctic Prince Charles Mountains. Precambrian Research, 167, 281–302.

Quigley, M.C., Liangjun, Y., Gregory, C., Corvino, A., Sandiford, M., Wilson, C.J.L., Xiaochan, L., 2008. U–Pb SHRIMP zircon geochronology and T–t–d history of the Kampa Dome, southern Tibet. Tectonophysics, 446, 97–113.

Corvino, A.F., Henjes-Kunst, F., 2007. A record of 2.5 and 1.1 billion year old crust in the Lawrence Hills, Antarctic Southern Prince Charles Mountains. Terra Antartica, 14, 13–30.

Corvino, A.F., Boger, S.D., Wilson, C.J.L., 2007. Metamorphic conditions during formation of a metapelitic sillimanite-garnet gneiss from Clemence Massif, Prince Charles Mountains, East Antarctica. In: Cooper A.K., Raymond C.R. et al. (Eds.) Antarctica: A Keystone in a Changing World-Online Proceedings of the 10th ISAES, USGS Open-File Report 2007-1047, Short Research Paper 062, 9 p.; doi:10.3133/of2007-1047.srp062.

Corvino, A.F., Boger, S.D., Wilson, C.J.L., Fitzsimons, I.C.W., 2005. Geology and SHRIMP U-Pb chronology of the Clemence Massif, central Prince Charles Mountains, East Antarctica. Terra Antartica, 12, 55–68.

Phillips, G., Kelsey, D.E., Corvino, A.F., Dutch, R. Continental reworking associated with overprinting orogenic events, southern Prince Charles Mountains, East Antarctica. Revised paper submitted to Journal of Petrology.

11 Introduction

Minerva Access is the Institutional Repository of The University of Melbourne

Author/s: Corvino, Adrian Felice

Title: Precambrian geology of the North Mawson Escarpment area, Prince Charles Mountains, Antarctica

Date: 2009

Citation: Corvino, A. F. (2009). Precambrian geology of the North Mawson Escarpment area, Prince Charles Mountains, Antarctica. PhD thesis, Faculty of Science, School of Earth Sciences, The University of Melbourne.

Publication Status: Unpublished

Persistent Link: http://hdl.handle.net/11343/35189

File Description: Abstract and Introduction

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