A geotraverse across two paleo-subduction zones in Tien Shan,Tajikistan |
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Affiliation: | 1. Geological Faculty, St. Petersburg State University, 7/9 University Embankment, St. Petersburg 199034, Russia;2. Natural History Museum, Centre for Russian and Central EurAsian Mineral Studies (CERCAMS), London SW7 5BD, UK;3. Institute of Geology, Earthquake Engineering and Seismology of the Academy Science of the Republic of Tajikistan, 267 Ainy St., Dushanbe 734063, Tajikistan;4. Deutsches GeoForschungsZentrum (GFZ), Telegrafenberg, D-14473, Potsdam, Germany;5. Institut für Geowissenschaften, Universität Mainz, D-55099 Mainz, Germany;6. Departamento de Ciencias de la Tierra y de la Construcción, Universidad de las Fuerzas Armadas ESPE, Sangolquì, Ecuador;7. Atlantic Branch of the P.P. Shirshov Institute of Oceanology, 1 Prospect Mira, Kaliningrad 236022, Russia;1. Department of Earth Sciences, Institute for Advanced Studies in Basic Sciences (IASBS), P.O. Box 45195-1159, Zanjan, Iran;2. State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;3. Department of Geology, Faculty of Sciences, University of Zanjan, Zanjan, Iran;1. MLR Key Laboratory of Metallogeny and Mineral Assessment, Institute of Mineral Resources, CAGS, Beijing 100037, China;2. Centre for Exploration Targeting, The University of Western Australia, Crawley, WA 6009, 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. Department of Earth Sciences, University of New Brunswick, Fredericton, NB, Canada;2. Barrick Gold Corporation, Montreal, BC, Canada;3. Department of Geological Sciences and Geological Engineering, Queen''s University, Kingston, ON, Canada;1. Department of Earth and Environmental Sciences and GeoBio-Center, LMU Munich, Theresienstr. 41, 80333, Munich, Germany;2. GeoZentrum Nordbayern, Universität Erlangen-Nürnberg, Schlossgarten 5a, 91054, Erlangen, Germany;3. Institut für Geologie, Universität Freiberg, Bernhard-von-Cotta Str. 2, 09599, Freiberg, Germany;4. Mineralogische Staatssammlung München, Theresienstr. 41, 80333, Munich, Germany;5. Sankt-Petersburg State University, University Embankment 7/9, 199034 Sankt-Petersburg, Russia;1. Geological Survey of Canada (GSC), 601 Booth Street, Ottawa, ON, K1A 0E8, Canada;2. Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10, DK-1350 Copenhagen K, Denmark |
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Abstract: | We present first LA-ICP-MS U–Pb zircon ages as well as geochemical and Sr–Nd–Pb isotope data for 14 magmatic rocks collected along ca. 400 km profile across the Chatkal-Kurama terrane in the Mogol-Tau and Kurama ranges and the Gissar Segment of the Tien Shan orogen in Tajikistan. These new data from supra-subduction and post-collisional magmatic rocks of two Late Paleozoic active margins constrain a tectonic model for terrane motions across two paleo-subduction zones: (1) The 425 Ma old Muzbulak granite of the Mogol-Tau range formed in a supra-subduction setting at the northern margin of the Turkestan Ocean. The north-dipping plate was subducted from the Early Silurian to the earliest Middle Devonian. Thereafter the northern side of the Turkestan Ocean remained a passive margin until the Early Carboniferous. (2) In the Early Carboniferous, subduction under the northern margin of the Turkestan Ocean resumed and the 315 to 305 Ma old Kara-Kiya, Muzbek, and Karamazar intrusions formed in a supra-subduction setting in the Mogol-Tau and Kurama ranges. (3) At the same time, in the Early Carboniferous, rifting of the southern passive margin of the Turkestan Ocean formed the short-lived Gissar Basin, separated from the Turkestan Ocean by the Gissar micro-continent. North-dipping subduction in the Gissar Basin is documented by the 315 Ma Kharangon plagiogranite and the voluminous ca. 321–312 Ma Andean-type supra-subduction Gissar batholith. The Kharangon and Khanaka gabbro-plagiogranite intrusions of the southern Gissar range have geochemical and Sr–Nd isotopic compositions (87Sr/86Sr(t) 0.7047–0.7056, εNd of + 1.5 to + 2.3) compatible with mantle-derived origin typical for plagiogranites associated with ophiolites. The supra-subduction rocks from the Gissar batholith and from the Mogol-Tau Kurama ranges have variably mixed Sr–Nd–Pb isotopic signatures (87Sr/86Sr(t) 0.7057–0.7064, εNd of − 2.1 to − 5.0) typical for continental arcs where mantle-derived magmas interact with continental crust. (4) In the latest Carboniferous, the Turkestan Ocean and the Gissar Basin were closed. The Early Permian Chinorsay (288 Ma) and Dara-i-pioz (267 Ma) post-collisional intrusions, emplaced in the northern part of the Gissar micro-continent after a long period of amagmatic evolution, have intraplate geochemical affinities and isotopic Sr–Nd–Pb isotopic compositions (87Sr/86Sr(t) 0.7074–0.7086, εNd of − 5.5 to − 7.4) indicating derivation from Precambrian continental crust which is supported by old Nd model ages (1.5 and 1.7 Ga), and by the presence of inherited zircon grains with ages 850–500 Ma in the Chinorsay granodiorite. The post-collisional intrusions in the southern Gissar and in the Mogol-Tau and Kurama ranges (297–286 Ma), emplaced directly after supra-subduction magmatic series, have geochemical and isotopic signatures of arc-related magmas. The distinct shoshonitic affinities of post-collisional intrusions in the Mogol-Tau and Kurama ranges are explained by the interaction of hot asthenospheric material with subduction-enriched wedge of lithospheric mantle due to slab break-off at post-collisional stage. Despite origination from different tectonic environments, all magmatic rocks have relatively old Nd model ages (1.7–1.0 Ga) indicating a significant proportion of Paleoproterozoic or older crustal material in their sources and their model ages are similar to those of post-collisional intrusions from the Alai and Kokshaal Segments of the South Tien Shan. |
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