Tectonic evolution of the South Tianshan orogen and adjacent regions,NW China: geochemical and age constraints of granitoid rocks |
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| Authors: | Jun Gao Lingli Long Reiner Klemd Qing Qian Dunyi Liu Xianming Xiong Wen Su Wei Liu Yitian Wang Fuqun Yang |
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| Institution: | 1.Key Laboratory of Mineral Resources, Institute of Geology and Geophysics,Chinese Academy of Sciences,Beijing,China;2.Beijing Institute of Geology for Mineral Resources,Beijing,China;3.GeoForschungszentrum Nordbayern,Universit?t Erlangen,Erlangen,Germany;4.Beijing SHRIMP Center,Chinese Academy of Geological Sciences,Beijing,China;5.College of Resources and Environmental Engineer,Guizhou University,Guiyang,China;6.Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing,China |
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| Abstract: | Geochemical and geochronological evidence was obtained from granitoids of the South Tianshan orogen and adjacent regions,
which consist of three individual tectonic domains, the Kazakhstan–Yili plate, the Central Tianshan Terrane and the Tarim
plate from north to south. The Central Tianshan Terrane is structurally bounded by the Early Paleozoic ‘Nikolaev Line–North
Nalati Fault’ and Late Paleozoic ‘Atbashy–Inyl’chek–South Nalati–Qawabulak Fault’ zones against the Kazakhstan–Yili and Tarim
plates, respectively. The meta-aluminous to weakly peraluminous granitic rocks, which are exposed along the Kekesu River and
the Bikai River across the Central Tianshan Terrane, have a tholeiitic, calc-alkaline or high-potassium calc-alkaline composition
(I-type). Geochemical trace element characteristics and the Y versus Rb–Nb or Y versus Nb discrimination diagrams favor a
continental arc setting for these granitoid rocks. SHRIMP U–Pb and LA-ICP-MS U–Pb zircon age data indicate that the magmatism
started at about 480 Ma, continued from 460 to 330 Ma and ended at about 275 Ma. The earlier magmatism (>470 Ma) is considered
to be the result of a simultaneous southward and northward subduction of the Terskey Ocean beneath the northern margin of
the Tarim plate and the Kazakhstan–Yili plate, respectively. The later magmatism (460–330 Ma) is related to the northward
subduction of the South Tianshan Ocean beneath the southern margin of the Kazakhstan–Yili–Central Tianshan plate. The dataset
presented here in conjunction with previously published data support a Late Paleozoic tectonic evolution of the South Tianshan
orogen, not a Triassic one, as recently suggested by SHRIMP U–Pb zircon dating for eclogites. |
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