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Revisiting the mechanisms of mid-tertiary uplift of the NE Tibetan Plateau

National Science Review 2023年第4期10卷 169-190页

作者： Hong-Hong Wei Guo-Li Wu Lin Ding Long-Gang Fan Lin Li Qing-Ren Meng State Key Laboratory of Tibetan Plateau Earth System Environment and Resources (TPESER) Institute of Tibetan Plateau Research Chinese Academy of Sciences Institute of Geomechanics Chinese Academy of Geological Sciences State Key Laboratory of Lithospheric Evolution Institute of Geology and Geophysics Chinese Academy of Sciences Department of Geosciences University of Arizona University of Chinese Academy of Sciences

Contrasting views exist on timing and mechanisms of tertiary crustal uplift in the NE Tibetan Plateau based on different approaches, with many models atributing surface uplift to crustal shortening. We carry out a comprehensive investigation of mid-tertiary stratigraphy, sedimentology, and volcanism in the West Qinling, Hoh Xil and Qaidam basin, and the results challenge previous views. It was held that the discordance between Oligocene and Miocene strata is an angular unconformity in the West Qinling, but our field observations show that it is actually a disconformity, indicative of vertical crustal uplifting rather than crustal shortening at the Oligocene to Miocene transition. Widespread occurrence of synsedimentary normal faults in mid-tertiary successions implicates supracrustal stretching. Miocene potassic–ultrapassic and mafic–ultramafic volcanics in the Hoh Xil and West Qinling suggest a crucial role of deep thermomechanical processes in generating crust-and mantle-sourced magmatism. Also noticeable are the continuity of mid-tertiary successions and absence of volcanics in the Qaidam basin. Based on a holistic assessment of stratigraphic–sedimentary processes, volcanic petrogenesis, and spatial variations of lithospheric thicknesses, we speculate that small-sale mantle convection might have been operating beneath northeast Tibet in the mid-tertiary. It is assumed that northward asthenospheric flow was impeded by thicker cratonic lithosphere of the Qaidam and Alxa blocks, thereby leading to edge convection. The edge-driven convection could bring about surface uplift, induce supracrustal stretching, and trigger vigorous volcanism in the Hoh Xil and West Qinling in the mid-tertiary period. This mechanism satisfactorily explains many key geologic phenomena that are hardly reconciled by previous models.

关键词： NE Tibetan Plateau mid-tertiary unconformity volcanism edge convection

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