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A Geological Traverse Across the Jack Hills Metasedimentary Belt

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A Geological Traverse Across the Jack Hills Metasedimentary Belt School of Science and Engineering Department of Applied Geology A Geological Traverse across the Jack Hills Metasedimentary Belt, Western Australia: Isotopic Constraints on the Distribution of Proterozoic Rocks and the Evolution of Hadean Crust Qian Wang This thesis is presented for the Degree of Doctor of Philosophy of Curtin University November 2014 Abstract A ~1010 m traverse across the Jack Hills Metasedimentary Belt was investigated in this study, starting from the BIF at the southern extremity of the belt and terminated at the boundary between amphibolite and granite at the northern extremity. This is the first detailed traverse that includes the fine-grained sediments in the northern part of the Jack Hills belt. The subaqueous deposits at the southern part of the belt give way to terrestrial deposits at the northern part, indicating significant shallowing of the basin. In this study, facies associations indicate a fan delta depositional environment. A total of 2819 concordant zircon ages were obtained out of ~6308 zircons analysed in this study, and these ages spread from 1618±22 Ma to 4381±5 Ma, with a prominent age peak at 3383 Ma. A total of sixteen (~0.5% of the total analysed) concordant Proterozoic zircon ages were identified from seven samples, ranging from 1618±22 Ma (212 m, JH039B-02) to 2473±20 Ma (514.5 m, JH096-04). The interleaving of Archean-Proterozoic successions, as indicated in previous studies confirm the existence of two different sedimentary associations, one formed in the Archean, the other formed in the Proterozoic. The samples which yielded Proterozoic ages were widely distributed along the belt and there is no relationship between rock-type and young zircon ages. The successions (65-202 m and 229-348 m) dominated by coarse-grained sandstone and conglomerate at the southern part of the traverse were likely deposited in the Archean. In this study, a total of 1093 zircons with ages from 1642 Ma to 4381 Ma from 46 samples were analysed for Lu-Hf isotopes. The 176Lu/177Hf ratios range from 0.000159 (JH152-24) to 0.004203 (JH152-50); and there were seven hundred and thirty-eight grains (67.5%) with 176Lu/177Hf ratios ≤0.001, with a prominent peak at ~0.0008. The 176Hf/177Hf ratios range from 0.279932 (JH058-055) to 0.281546 (JH039A-22), with a prominent peak at ~0.28035. The εHf(t) values for all zircons range from -22.1 (JH039A-47) to 5.5 (JH034-049), and the majority of the dataset (94.6%) have negative εHf(t) values, with only fifty-nine zircons (5.4%) having positive εHf(t) values that spread from 0.1 to 5.5. The prominent εHf(t) peak is at -4.2, with a secondary peak at -7.6. The negative εHf(t) values make up 92% of the Hadean population, indicating the Hf isotope data do not favour the existence of a strongly depleted Hadean mantle i contribution, or significant juvenile input into the parental magmas to the Jack Hills detrital zircons as early as ~4.4-4.5 Ga. The best fit of the Jack Hills detrital zircon data involves using the single-stage TDM model age. This implies that the majority of the Hadean zircons likely evolved from a primitive source. The Hf isotope data support the notion of long-lived, mafic dominant Hadean crust, which could only endure on the Earth’s surface in the absence of subduction, thus mitigating against Hadean plate tectonics. The peaks of εHf(t) at ~3.2 Ga, 3.4-3.5 Ga, 3.8-3.9 Ga, and 4.0-4.2 Ga in this study are consistent with the 3.3-3.4 Ga, 3.8 Ga and 4.2 Ga peaks in the global dataset. The preferred explanation to these peaks is mixture of juvenile material with extensive crustal reworking involved in burial and remelting. For zircons with crystallization ages around 2.65 Ga, the potential source could be the 2654±7 Ma monzogranites located immediately south of the Jack Hills belt. For the zircons younger than 2.6 Ga with εHf(t) values ranging from -22.1 to 1.0, the source rocks could potentially be granitoids or even more mafic rocks. Meeberrie gneiss could possibly have been a major source of Jack Hills zircons with ages from 3.3 to 3.7 Ga. The multiple components of the Meeberrie gneiss can explain the large range of εHf(t) values of the Jack Hills zircons. However, the source rock for the >3.8 Ga Jack Hills zircons (N=144) remains unknown. A weighted mean 207Pb/206Pb age of 2652±9 Ma was obtained for metamorphic monazite in a fine-grained mica sandstone sample (JH10085, 459 m) in the centre of the traverse east of Eranondoo Hill. This result confirms that the Archean rocks in the central part of the Jack Hills belt experienced metamorphism at ~2.65 Ga. ii Acknowledgements Professor Simon Wilde supervised this thesis. His guidance and support was always available and greatly appreciated. His supervision in the laboratory protocols, his effort in organising two field trips and help with sample collection are also gratefully acknowledged. Both his patience in examining raw isotope data and meticulous guidance in editing the manuscript are particularly valued. I benefitted from his rigorous attitude towards scientific consistency. Professor Birger Rusmussen was an associate supervisor of this project. He provided guidance during the EDS analyses, polished-section drilling and SHRIMP monazite geochronology process. His advice on interpretation of monazite data is also appreciated. Bob Crossley and Professor Yang Jinhui (杨进辉) helped by making and organising the thin- and polished-sections, respectively. Dr Ron Watkins and Professor Neal McNaughton generously offered equipment for sample preparation, and Dr Marion Grange demonstrated the mineral separation process, which are all greatly appreciated. Dr. Janet Muhling at the UWA Centre of Microscopy and Microanalysis provided training and advice with EDS analyses, and Elaine Miller provided training and help with imaging on the Curtin SEM. Dr. Monika Kusiak helped prepare some high resolution CL images. Dr. Allen Kennedy contributed in describing the SHRIMP analytical techniques, data processing and interpretation, and also offered me a part time job in the SHRIMP lab at the John De Laeter Centre. Hao Gao provided training in the SHRIMP analytical procedures. I have benefitted from numerous discussions regarding SHRIMP analytical techiniques, data reduction and interpretation of monazite with Dr. Daniel Dunkley. SHRIMP data collection was a lot less stressful with the technical assistance from Adam Frew. Exchange of ideas with Professor Pete Kinny has contributed in understanding the Lu-Hf data processing and interpretation. Professor Wu Fuyuan (吴福元) and Professor Yang Jinhui (杨进辉) offered access to the ICP-MS for zircon Lu-Hf isotope analyses at the Institute of Geology and Geophysics, Chinese Academy of Sciences in Beijing. Dr. Yang Yueheng (杨岳衡) provided technical support to the ICP-MS. My fellow PhD student Ge Rongfeng (葛 荣峰) offered great help during the analytical process. iii Professor Sun Yong ( 孙勇) offered access to the State Key Laboratory of Continental Dynamics, Northwestern University, in Xi’an, China. Dr. Liu Xiaoming (柳小明), Dr. Zhang Hong (张红) and Dr. Diwu Chunrong (第五春荣) offered technical support to the ICP-MS for zircon geochronology and zircon Lu-Hf isotope analyses. Bao Zhi’an (包志安), Xiao Zhibin (肖志斌), Chen Kaiyun (陈开运) and many other friends at the Department of Geology, Northwest University in Xi’an, offered great help in the process of zircon isotopic analyses, including 20 days of night shift. Their help was essential for me to collect the large quantity of zircon isotope analyses on time. Tian Xinhong (田新红) provided help in countless ways during my time in Xi’an. I offer thanks to the Government of People’s Republic of China for awarding me a China Scholarship Council Scholarship (CSC) for the first three years of my study, and I also offer thanks to The Institute for Geoscience Research (TIGeR) and my supervisor Professor Simon Wilde for providing finance support for another one and half years of my study. My parents supported my overseas study and always encouraged me to complete my project. My husband Xue Song always supported me. Special thanks to all my family. iv Contents Abstract .................................................................................................................... i Acknowledgements .................................................................................................. iii Contents .................................................................................................................. v List of Tables ...........................................................................................................ix List of Figures .......................................................................................................... x Chapter 1 Introduction ............................................................................................. 1 1.1 Location and Access ...................................................................................... 1 1.2 Introduction to the Study Area ........................................................................ 1 1.3 Objectives ...................................................................................................... 2 1.4 Methodology ................................................................................................... 2 1.4.1 Fieldwork ................................................................................................. 2 1.4.2 Analytical Techniques .............................................................................. 3 1.5
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