Tectono-magmatic rejuvenation of the Qaidam craton, northern Tibet

International audienceAscertaining the enigmatic characteristics of the crystalline basement of the Qaidam basin, the deepestintracontinental basin yet located in the highest orogenic plateau with the thickest continental crust, has broadimplications 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 theQaidamand 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 involvedinto three tectono-magmatic episodes. Similar whole-rock geochemistry and Sr–Nd isotopiccharacteristics between the Early Neoproterozoic granitoids beneath the Qaidam basin and the contemporaneousbasement rocks in the surrounding orogenic belts confirm the existence of pervasive Early Neoproterozoicmetamorphism and magmatism along the present-day northern Tibetan Plateau. By comparing the trace andrare 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 granitoidsfromthe surrounding orogenic belts,we assert that the Proto-Tethys subduction events thatwere recordedwithin the Eastern Kunlun, Altyn Tagh and the Qilian Shan orogenic belts,were different. They generated distinctivesubduction-related arc magmas, whereas the closure of the oceanic basins resulted in the amalgamation ofthe orogenic belts inducing subsequent extensive post-collisional magmatism within the Qaidam block. Thewidespread Permian and Triassic granitoids beneath the northwestern/northern Qaidam basin mainly involveda lower crust or a crust-mantle source including Mesoproterozoic crust. They demonstrate that the influence ofthe 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 tectonomagmaticrejuvenated 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 QilianShan transpressional system to the northeast, the Qaidam block forms a relatively stable domain that escapedfrom significant Cenozoic deformation