Depositional Record Constraints on Late Cenozoic Uplift of Tianshan and Tectonic Transformation in Kuqa Depression, West China
LI Zhong1 WANG Qing-chen1 WANG Dao-xuan2 LIN Wei1 1(Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029) 2(Hefei University of Industry, Hefei 230009)
Based on system research on detrital sediments in different scales, it is found that molasse-like deposits, instable (easy abrasive) detrital grains and mineral-assemblages were developed in the Kuqa depression, the south foot of the Tianshan, in Neogene, especially after Miocene. It is also presented that gradual southward migration of alluvial depositional fronts and depositional depocenters with near east-west strike occurred since Cretaceous. However, evident changes of the above migration trend happen since Pliocene, in which large-scale southward migration of alluvial depositional systems but relative northward migration of depositional depocenters occurred simultaneously, and current north depositional boundary is near present basin-mountain boundary between Kuqa depression and Tianshan, which attributes to syndepositional normal faults of southward dip. Combined with data from tectonic and paleoclimate reserches, it is explained that the above depositional records resulted from the tectonic transformation processes in Late Cenozoic, in which gravity-extension and gravity-collapse occurred in the shallow tectosphere of the Kuqa depression-Tianshan since Pliocene due to intensive uplift of the Tianshan under continuous extrusion stress in Late Cenozoic. The conclusion on tectonic transformation processes, presented in the paper, revise the past views on Cenozoic dynamic mechanism of structural accommodation, which was explained with sole southward thrusting pattern of the Tianshan under extrusion stress regimes.