Geodynamic evolution of the western Tien Shan,Uzbekistan: Insights from U-Pb SHRIMP geochronology and Sr-Nd-Pb-Hf isotope mapping of granitoids |
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| Institution: | 1. Natural History Museum, Department of Earth Sciences, CERCAMS, London SW7 5BD, UK;2. St. Petersburg State University, Geological Faculty, St. Petersburg 199034, Russia;3. All Russian Geological Research Institute (VSEGEI), St. Petersburg 199106, Russia;4. Macquarie University, CCFS/GEMOC, NSW 2109, Sydney, Australia;5. British Geological Survey, Keyworth, Nottingham NG12 5GG, UK;6. National University of Uzbekistan, Department of Geology, Tashkent, Uzbekistan;7. Institute of Mineral Resources, Gozkomgeologiya, Tashkent, Uzbekistan;1. SOA Key Laboratory of Submarine Geoscience, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;2. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China;3. Geological Survey of Jiangsu Province, Nanjing 210018, China;4. Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia;1. Institute of Mineralogy, TU Bergakademie Freiberg, Brennhausgasse 14, 09596 Freiberg,Germany;2. Centre for Russian and Central EurAsian Mineral Studies (CERCAMS), Department of Earth Sciences, Natural History Museum, London SW7 5BD, Cromwell Road, UK;3. Federal Institute for Geosciences and Natural Resources (BGR), Stilleweg 2, 30655 Hannover, Germany;4. Center of Isotopic Research, All-Russian Geological Research Institute (CIR VSEGEI), Sredny Pr. 74, 199106 St. Petersburg, Russia;5. Institute of Mineralogy, Geochemistry and Crystal Chemistry of Rare Elements (IMGRE RAS), ul. Veresaeva 15, 121357 Moscow, Russia;1. College of Earth Sciences, Jilin University, Changchun 130061, China;2. State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210046, China;3. Xinjiang Research Center for Mineral Resources, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi 830011, China;4. School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China;5. Xinjiang Bureau of Geology and Mineral Resources, Urumqi, Xinjiang 830000, China |
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| Abstract: | Sr-Nd-Pb-Hf isotope mapping combined with U-Pb zircon SHRIMP ages of granitoids from four sampling profiles across terrane boundaries in Uzbekistan reveal distinct reservoir types (cratonic and accretionary), witnessed by the diverse nature and origin of the predominant Paleozoic granitic magmatism that provided hosts for major ore-bodies. The study region comprises four major terranes, including 1) the Sultan-Uvais terrane, 2) the Kyzylkum-Nurata Segment and 3) the Gissar Segment of the South Tien Shan and 4) the Chatkal-Kurama terrane of the Middle Tien Shan. Sr-Nd isotope analyses show a wide range of εNdt (− 5 to + 7) and (87Sr/86Sr)t of 0.704–0.707, indicating involvement of both mantle-derived material and older crustal sources. A wide range of Hf-isotope compositions found in zircons of Chatkal-Kurama granites, Middle Tien Shan (εHf mainly ~ − 5 to + 5), could be due to recycling of older crustal protolith(s); in particular, the earliest (Silurian) granites may be directly derived from 1.5 to 1.7 Ga lower crust. In the Southern Tien Shan, some involvement of subducted oceanic crust is evidenced by strongly juvenile εHft values of up to + 14 and + 16 (Sultan-Uvais, Teskuduk-Kyzylkum). Permo-Carboniferous granitoids, which occur across all terranes also exhibit a wide range of isotope signatures, corresponding to Mesoproterozoic–Neoproterozoic crustal protoliths with a westward increase in juvenile contributions. Pb isotopes (whole-rock) imply the dominance of a crustal component and crust-mantle mixing processes. New age data confirmed: 1) old age of the Turkestan Ocean (505 Ma in Sultan-Uvais), 2) fragments of Silurian island arcs in the accretionary complex of the Chatkal-Kurama terrane (granites of 429–416 Ma) and in the upper allochthon of the South Tien Shan (gabbro 438 Ma in Tamdytau), and 3) a significant volume of granitoid magmatism of subduction or early-collisional stages (around 320–310 Ma) in the Chatkal-Kurama Segment and especially in the Gissar Segment. The westernmost part of the Tien Shan is characterized by multiple subduction processes responsible for 300 million years of geodynamic evolution history (accretionary collage, crustal growth) with the pre-Mesozoic crust formation concluded by Permian post-collisional extensional magmatism. |
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