Low-thermochronology Constraints The Mesozoic-Cenozoic Tectonic Events From The Xining Basin And Eastern Qilian Shan

The uplifting process and extension mechanism of the Tibetan Plateau have always been a hot topic in geological research.Due to the vast area of the Plateau,which the differences in internal tectonic activities.There are still differences in understanding of the uplifting time,process and mechanism of the Plateau.Therefore,it is necessary to obtain more spatial-temporal evidence of tectonic uplifted evolution in key areas of the Tibetan Plateau through various research methods to test existing views or put forward new understandings.Since the Cenozoic,a series of typical basin-mountain couple tectonic geomorphic pattern of orogenic belts and basin combinations has been formed in the northeastern margin of the Tibetan Plateau.The Qilian Shan(the northeastern boundary of the Plateau)was uplifted by the Caledonian orogenic belt in Cenozoic,which is the key to the study of the remote effect of the India-Eurasia plate collision and the dynamic process of the Tibetan Plateau.However,it's still not clear about the Cenozoic Qilian Shan when and how uplifted.Xining Basin is located at the intersection of Qilian Shan,East Kunlun Shan and West Qinling orogenic belts.Its formation and evolution are closely related to the tectonic activities of the surrounding orogenic belts,and it is a key area to study the tectonic evolution of the Qilian Shan and the northeastern margin of the Tibetan Plateau.In this paper,the Cenozoic strata of Xining Basin and nearly Eastern Qilian Shan have been selected as the research objects.Taking basin-mountain coupling as the main line,using low-temperature thermochronology to combine basin and surrounding mountains research approach.This paper mainly studies the detrital apatite fission track age of the Cenozoic sediment system in Xining Basin and the thermal history simulation of bedrock apatite fission track in the eastern Qilian Shan.Combined with the previous studies,this paper reveals the major tectonic uplifted and denudation events of the Qilian Shan in the northeastern margin of the Tibetan Plateau,providing cryogenic chronology evidence for the tectonic evolution of the Xining Basin.The main insights gained are as follows:(1)The unannealed detrital apatite fission track age of the Xining basin is 153-138Ma(Late Jurassic-Early Cretaceous)and 111.7-82Ma(Late Cretaceous).The structural cooling signals mainly come from the Qilian Shan and are also reflected in the thermal history simulation results of apatite fission track in the bedrock of the Qilian Shan.These two stages of Mesozoic tectonic uplift and denudation events in the Qilian Shan may be in response to the northward subduction of the Bangong Lake-Nujiang Tethys Ocean in the southern Eurasian continent and the collision between the Lhasa and Qiangtang terrane.(2)The results of detrital apatite fission track age components in Xining basin and thermal simulation of apatite fission track in Qilian Shan reveals there have been at least four major uplift/exhalation events(61.9-41 Ma,39.2-32 Ma,27.9-15 Ma and 12-5 Ma)in the Qilian Shan since the Cenozoic.During 61.9-41Ma(Paleocene-Eocene),the Qilian Shan tectonic cooling event was a response to the quasi-synchronous transfer of the collision stress between India and Eurasia plate to the northeastern margin of the Tibetan plateau.During the 12-5Ma(Late Miocene),strong tectonic uplift of the Qilian Shan led to formation the present geomorphic pattern in the northeastern margin of the Tibetan plateau.(3)The tectonic activation in different parts of the northeastern margin of the Tibetan Plateau during the Cenozoic is influenced by the Mesozoic tectonic weakness zone.The Qilian Shan Cenozoic deformation has the characteristics of multi-stage and quasisynchronous,which the synchronous growth of the north and south sides has significant influence on the formation/evolution of the Xining Basin.