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Tectonic Evolution of the Early Archaean Doolena Gap Greenstone Belt, East Pilbara Terrane, Western Australia

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Tectonic Evolution of the Early Archaean Doolena Gap Greenstone Belt, East Pilbara Terrane, Western Australia TECTONIC EVOLUTION OF THE EARLY ARCHAEAN DOOLENA GAP GREENSTONE BELT, EAST PILBARA TERRANE, WESTERN AUSTRALIA by Daniel Wiemer (Dipl. Geol./M.Sc.) ____________________________________________ Submitted in total fulfillment of the requirements for the degree of Doctor of Philosophy (Ph.D.) Brisbane, 2017 School of Earth, Environmental and Biological Sciences Science and Engineering Faculty Queensland University of Technology Supervisor: Dr. David T. Murphy Co-supervisor: Dr. Christoph E. Schrank ii QUT Verified Signature iii Abstract Earth’s oldest preserved crust is characterised by a distinctive crustal architecture of large ovoid granitic domes surrounded by curvilinear supracrustal greenstone belts. Such dome-and-keel morphology is not generated in the present-day Earth as part of plate tectonics. This indicates that the crustal fragments preserved from the early Earth, which had higher heat generation and therefore higher temperatures, formed in a distinct non-plate tectonic style tectono-magmatic regime. Here I investigate the lithological associations, the magmatic contributions and the structural kinematics that gave rise to the distinctive Archean dome and keel morphology. In doing so I test the model of partial convective overturn for the formation of the dome-and-keel crustal architecture in which dense mafic crust overlying lower density felsic crust leads to buoyancy instabilities and crustal-scale reorganization. The 3530- 3225 Ma East Pilbara Terrane, Western Australia, contains the best preserved lithological and structural inventory associated with dome-and-keel formation, making it the archetypical early Archean dome-and-keel terrane and the perfect natural laboratory for investigating early Archaean tectonic processes. Here I present a detailed lithostratigraphic, structural, petrological, geochemical, and geochronological study of a well exposed geological transect through the dome-and-keel terrane of the transition between the western Doolena Gap greenstone belt and the Muccan Granitic Complex. I aim to address the following fundamental research problems and questions: i) What is the lithostratigraphic and structural anatomy of a well exposed transect between little altered lowermost greenschist-facies lithologies in the Doolena Gap greenstone belt and granitiod gneisses of the adjacent Muccan Granitic Complex and how do they relate to dome-and-keel formation? ii) Is there evidence for the development of a buoyantly unstable crustal configuration, such as significant felsic crustal components that predate mafic volcanism and lateral thickness and compositional variations of greenstone formations? iii) When did the major phase(s) of partial convective overturn that led to the dome-and-keel morphology occur? I have identified a deformation event that includes tight fold development in both the Doolena Gap greenstone belt and marginal gneisses of the Muccan Granitic Complex that predates the formation of a 45o unconformity upon which the 3427-3350 Ma Strelley Pool Formation was deposited. The nature and kinematics of this deformation event are consistent with dome-up and keel-down relative motion and indicates a partial convective overturn event between 3460 Ma, the lower age of the Duffer Formation of the greenstone belt and 3427 Ma, the minimum age of the Strelley Pool Formation, that precedes the regional 3310 Ma partial convective overturn event in the East Pilbara Terrane. I have identified a new suite of co-magmatic granitic gneisses, the Doolena Suite (ca. 3500-3590 Ma) along the margin of the Muccan granitic Complex that represents the oldest coherent lithological formation in the East Pilbara Terrane and predates the oldest greenstone belts. This demonstrates that felsic crust was present in the precursor crust upon which the Pilbara Supergroup was deposited. Keywords: East Pilbara Terrane, Archaean tectonics, dome-and-keel, crustal evolution, Doolena Gap greenstone belt; iv Publications Chapter 2: Wiemer, D., Schrank, C. E., Murphy, D. T., and Hickman, A. H., 2016: Lithostratigraphy and structure of the early Archaean Doolena Gap greenstone belt, East Pilbara Terrane, Western Australia. Precambrian Research, 282, 121-138 Conference abstracts Wiemer, D., Allen, C. M., Murphy, D. T., and Kinaev, I., 2017: Effects of thermal annealing and chemical abrasion on the U-Pb systematics, and the microstructure of complex, metamict ~3.5 billion year old zircon: insights for U-Pb LA-ICP-MS dating. AMAS 14th Biennial Symposium, Brisbane Allen, C. M., Wiemer, D., and Murphy, D. T., 2016: Improving LA-ICP-MS dating techniques: experiments on zircon from a 3.51 Ga dioritic gneiss, East Pilbara Terrane, Western Australia. GSA Annual Meeting, Denver Wiemer, D., Schrank, C. E., Murphy, D. T., and Hickman, A. H., 2015: Structural development of the early Archaean Doolena Gap greenstone belt, East Pilbara Terrane (Western Australia). SGTSG, Caloundra Burke-Shyne, D., Wiemer, D., Schrank, C. E., and Murphy, D. T., 2015: Carbonate alteration is the dominant weakening mechanism in the Doolena Gap Greenstone Belt preserving the keel rock in a dome-and-keel terrane. SGTSG, Caloundra Murphy, D. T., Trofimovs, J., Hepple, R. A., Wiemer, D., Kemp, A. I. S., and Hickman, A. H., 2015: Pillow basalts from the Mount Ada Basalt, Warrawoona Group, Pilbara Craton: implications for the initiation of granite-greenstone terrains. Goldschmidt, Prague Wiemer, D., Schrank, C. E., and Murphy, D. T., 2014: Lithostratigraphy and structure of the early Archaean Doolena Gap Greenstone Belt, East Pilbara Terrane (EPT), Western Australia. AGU Fall Meeting, San Francisco v Acknowledgements I highly acknowledge my supervisory team David Murphy and Christoph Schrank for their trust, patience, guidance and mentoring. Thank you! You are both remarkable personally and as scientists. I thank Charlotte Allen for her assistance and mentoring in zircon geochronology and for giving me shelter for a while. Scott Bryan is acknowledged for critically reviewing various stages of my PhD research. David Gust is thanked for letting me take part in teaching of undergraduate students. Arthur Hickman and the Geological Survey of Western Australia are highly acknowledged for fieldwork logistics. Critical review by Arthur Hickman has greatly improved this thesis, particularly the second Chapter. I thank the administrative backbone of the QUT system: Sarie Gould, Courtney Innes, Noelene Davis, Tiziana La Mendola and others. I highly acknowledge following QUT staff members and colleagues for training and assistance in various analytical methods: Aarshi Bhargav, Henny Cathey, Karine Moromizato, Llew Rintoul, Gus Luthje, Donald McAuley, Irina Kinaev, Sanjleena Singh, Peter Hines, Mitch DeBruyn, Chris East, Linda Nothdurft, Shane Russell, Natalia Danilova, Alex Hepple, David Steele. I acknowledge Charles Verdel, Gang Xia and Dario Hogg from the University of Queensland for guidance and assistance in lab work I highly acknowledge John De Kruijff, Thomas Spring, Shosh O’Connor, Ali Sternes and Duncan Burke-Shyne for helping hands during my fieldwork. Thanks to the Ultimate Frisbee Team and the EEBS Seminars I thank all my housemates for tolerating me over the years: Joania, Yazu, Ella, Julia, Carol, Joakim, Bronwen, Charlotte & David, and James. Finally, my family, friends and mates – I love You!, You know who you are! vi “The Earth is not forever, But just to remain for a short while…” (Scott R. Weinrich, Dreamwheel, 1999) vii viii TABLE OF CONTENTS Page Declaration of Original Authorship iii Abstract iv Publications v Acknowledgements vi List of Figures xi List of Tables xii _______________________________________________________________________________ CHAPTER 1 1 INTRODUCTION 1.1 Research Background 1 1.1.1 Earth’s thermal evolution, and the theoretical consequences for Archaean geodynamics 5 1.1.2 Archaean dome-and-keel terranes 6 1.1.2.1 Model for dome-and-keel formation in the East Pilbara Terrane 7 1.2 Research Problems and Questions 7 1.3 Aim of the Research 10 1.4 Research Philosophy and Methodology 11 1.5 Outline of Chapters 11 _______________________________________________________________________________ CHAPTER 2 13 LITHOSTRATIGRAPHY AND STRUCTURE OF THE EARLY ARCHAEAN DOOLENA GAP GREENSTONE BELT, EAST PILBARA TERRANE, WESTERN AUSTRALIA 2.1 Abstract 13 2.2 Introduction 15 2.3 Regional Geology and Tectonic Framework of the East Pilbara Terrane 16 2.4 Geological Setting of the Study Area 18 2.5 Lithostratigraphy and Structure 21 2.5.1 Muccan Granitic Complex 21 2.5.1.1 Lithological components and structure within the Muccan Granitic Complex 21 2.5.1.2 Deformational micro-textures and metamorphism within the Muccan Granitic Complex 23 2.5.2 South Muccan Shear Zone 25 2.5.2.1 Lithological components and structures within the South Muccan Shear Zone 25 2.5.2.2 Deformational micro-textures and metamorphism within the South Muccan Shear Zone 25 2.5.3 Central Fold Belt 27 2.5.3.1 Lithological components within the Central Fold Belt 27 2.5.3.2 Structures and deformational events within the Central Fold Belt 27 2.5.3.3 Micro-textures, deformational intensity and metasomatism within the Central Fold Belt 30 2.5.4 Southern Low-Strain Belt 32 2.5.4.1 Lithological components and structures within the southern Low-Strain Belt 32 2.5.4.2 Micro-textures, deformation and metamorphism within the Low-Strain Belt 35 2.5.4.3 Lithostratigraphy of the Low-Strain Belt 35 a) Mount Ada Basalt 35 b) Felsic volcanic – sedimentary succession (Duffer Formation) 37 c) Strelley Pool Formation
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