Geochemistry and geodynamic implications of the Triassic bimodal magmatism from Western Kunlun Orogen,northwest China |
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Authors: | Email author" target="_blank">Shiyong?LiaoEmail author Email author" target="_blank">Yaohui?JiangEmail author Qin?Zhou Wanzhi?Yang Guodong?Jin Peng?Zhao |
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Institution: | (1) State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, 210093 Nanjing, China;(2) Chengdu Institute of Geology and Mineral Resources, Chinese Geological Survey, 2/3 No. 1 Ring Road (N), 610082 Chengdu, China;(3) Xinjiang Institute of Geological Survey, 830000 Urumqi, China;(4) Nanjing Institute of Geology and Mineral Resources, Chinese Geological Survey, 210016 Nanjing, China |
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Abstract: | The Western Kunlun Orogen occupies a key tectonic position at the junction between the Tarim block and the Tethyan domain.
However, the late Paleozoic to early Mesozoic, especially the middle to late Triassic tectonic evolution history of the Western
Kunlun Orogen remains controversial. This study reports SHRIMP zircon U–Pb ages and geochemical as well as Sr–Nd–Hf isotopic
data for middle to late Triassic Taer pluton in Western Kunlun Orogen, Northwest China. The Taer pluton shows a strong bimodal
distribution of compositions, with the felsic rocks dominant and the mafic rocks subordinate. Zircon U–Pb dating reveals that
the coexisting mafic and felsic rocks are coeval, both emplacing in a period between 234 and 225 Ma. Most of the studied rocks
are potassium rich and can be classified into high-K calc-alkaline to shoshonitic series. They are also strongly enriched
in LREE, LILE and depleted in HFSE with strong negative Ti and Nb anomalies, and characterized by enriched Sr–Nd–Hf isotopic
signatures. Detailed geochemical and isotopic studies indicate that the Taer pluton was emplaced in a post-collisional extensional
setting, with the mafic rocks derived from partial melting of the enriched continental lithospheric mantle in the spinel facies
field, and the felsic rocks formed by anatexis of newly underplated basaltic rocks. The existence of middle to late Triassic
post-collisional magmas in Western Kunlun region suggests that the final closure of Paleo-Tethys and the initial collision
between the Western Kunlun and the Qiangtang terranes may have happened before ~234 Ma, most probably in late Permian, rather
than in late Triassic or early Jurassic. In assistance with other geological evidences, such as the presence of early Triassic
to late Triassic/early Jurassic S-type magmatism, terrestrial molasse depositions, regional unconformities, and strong deformation,
we propose that the Western Kunlun Orogen may have undergone a long post-collisional intracontinental process from early Triassic
to late Triassic/early Jurassic. |
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