Tectono-magmatic rejuvenation of the Qaidam craton, northern Tibet

Abstract : Ascertaining the enigmatic characteristics of the crystalline basement of the Qaidam basin, the deepest intracontinental basin yet located in the highest orogenic plateau with the thickest continental crust, has broad implications for the Cenozoic basin evolution, in particular, and intracontinental tectonics of Asia, in general. We carried out a comprehensive investigation on the ages and geochemical-isotopic characteristics of the Qaidamand Suganhu basement rocks obtained fromdrill-cores. Petrological observations and U-Pb zircon dating (LA-ICP-MS) of granitoid samples fromdrill cores indicate that EarlyNeoproterozoic, Early Paleozoic and Late Paleozoic- Mesozoic intrusions are largely represented, suggesting that the Qaidam and Suganhu blocks were involved into three tectono-magmatic episodes. Similar whole-rock geochemistry and Sr–Nd isotopic characteristics between the Early Neoproterozoic granitoids beneath the Qaidam basin and the contemporaneous basement rocks in the surrounding orogenic belts confirm the existence of pervasive Early Neoproterozoic metamorphism and magmatism along the present-day northern Tibetan Plateau. By comparing the trace and rare earth elements patterns as well as the Sr-Nd compositions of the Ordovician arc-related granitoids and Silurian- Devonian post-collisional granitoids beneath the Qaidamand Suganhu basins with the corresponding granitoids fromthe surrounding orogenic belts,we assert that the Proto-Tethys subduction events thatwere recorded within the Eastern Kunlun, Altyn Tagh and the Qilian Shan orogenic belts,were different. They generated distinctive subduction-related arc magmas, whereas the closure of the oceanic basins resulted in the amalgamation of the orogenic belts inducing subsequent extensive post-collisional magmatism within the Qaidam block. The widespread Permian and Triassic granitoids beneath the northwestern/northern Qaidam basin mainly involved a lower crust or a crust-mantle source including Mesoproterozoic crust. They demonstrate that the influence of the Paleo-Tethys evolution penetrated the Qaidamblock northwards, reaching to the northern edges of the block. We conclude that the Qaidam block is not a craton as typical as the rigid Tarim block, but pertains to a tectonomagmatic rejuvenated craton, which is not mechanically-stronger than its surrounding regions. However, trapped between the lithospheric left lateral strike-slip Altyn Tagh fault system to the northwest and the Qilian Shan transpressional system to the northeast, the Qaidam block forms a relatively stable domain that escaped from significant Cenozoic deformation.
Type de document :
Article dans une revue
Gondwana Research, Elsevier, 2017, 49, pp.248-263. 〈10.1016/j.gr.2017.06.004〉
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Soumis le : mardi 27 juin 2017 - 08:23:24
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Feng Cheng, Marc Jolivet, Erwan Hallot, Daowei Zhang, Changhao Zhang, et al.. Tectono-magmatic rejuvenation of the Qaidam craton, northern Tibet. Gondwana Research, Elsevier, 2017, 49, pp.248-263. 〈10.1016/j.gr.2017.06.004〉. 〈insu-01547648〉



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