Cenozoic Tectonic Uplift Of South Qilian Shan: Constriants From Apatite (U-Th)/He Thermochronology

The collision of India with Asia is perhaps the most profound tectonic event during the past 100 Ma.It provides us a natural labtorary of studying plate tectonics of continental collision,at the same time,it has a strong relationship with interior Asia and global climate and environment change.Understanding the evolution of Northeastern Tibetan Plateau growth plays an important role in realization of kinematics,geodynamics and climatic consequences of large-scale Tibetan plateau orogensis.Despite these important implications,models to explain plateau-forming mechanism have been on debates.The Qilian Shan lies on the northeastern boundary of Tibetan Plateau,is characterized by large folds and thrust faults.Most researches indicated the Qilian Shan experienced deformation and tectonic uplift during Cenozoic.As a result,in some extent,The Qilian Shan recorded the tectonic uplift information of Tibetan Plateau.A lot of research work has been devoted to Qilian Shan in diverse ways,however,there remain dispute about the initial timing and structuuural evolution of Qilian Shan.As a result,there needs more study to get more information of tectonic uplift of Qilian Shan.Apatite(U-Th)/He is a new geologic method in recent 20 years,as it has the low closure temperature,and has been widly used to study tectonic exhumation.In this study,we target eleven basic granite rock of south Qilian Shan.And present new low-temperature thermochronology apatite(U-Th)/He ages on the hanging wall of the Qaidam Shan fault which lies on the southern margin of the Qilian shan and Danghe Nanshan fault which lies on the northern margin of the Qilian shan.The main conclusions are as follows:1?Results from the Qaidam Shan samples show He age has no correlation with elevation,He age show small range distribution(10-15Ma).So we infer that Qaidam shan expericed rapid exhumation at 15-10 Ma,which could be attributed to the motion of faulting and topographic growth of the North Qaidam Thrust system,the mean exhumation rate is 200-300m/Ma.2?Results from the Danghe-Nan Shan samples range from 8-63 Ma,which show positive age-elevation relationship with a distinct change in apparent exhumation rate at 8.3Ma.We infer that the Danghe Nanshan experienced two phases of tectonic uplift,the first event occurred at early Cenozoic(63-50Ma)with mean exhumation rate of 70m/Ma,The second event occurred at 8.3Ma with mean exhumation rate of 324m/Ma,which obviously stronger than the former event.The results are consistent with previous sedimentological studies of the peripheral basin,which indicated rapid increase of sediment accumulation rates around this time interval.3?By synthesizing geologic,sedimentologic and thermochronometric data,we present early Cenozoic slow exhumation and a phase of regional rapid deformation in the mid-late Miocene of Qilian Shan.We concluded that far-field effect of India and Asia collision has been reached the Qilian Shan in early Cenozoic,the south Qilian Shan has been uplifted at early Cenozoic,the central Qilian Shan and north Qilian Shan uplifted later during middle to late Miocene.