Exhumation History Of The Centre Tibetan Plateau:evidence From Fission-track Thermochronology Of The Paleogene Sediments In The Hoh Xil Basin

The sediments in the basin faithfully recorded the complete signal of the uplift of the peripheral orogenic belt.The Hoh Xil Basin,located in the hinterland of the Qinghai-Tibet Plateau,is the largest sedimentary basin in northern Tibet,with a cumulative sediment thickness of more than 5,800 meters.The north and south sides of the basin are the Qiangtang block,the Tanggula mountain orogenic belt and the East Kunlun orogenic belt.Therefore,the study of sediments in the Hoh Xil Basin can trace the tectonic evolution process of these two major orogenic belts,and provide key information for discussing major scientific issues such as the tectonic events of the northern plateau,the process and method of plateau uplifting,and the paleo altitude of the plateau in different periods.Predecessors have done a lot of research on the evolution of the depositional environment and its magnetostratigraphy in the Hoh Xil Basin,providing the basic prerequisite guarantee for the sedimentary sequence and sedimentary chronology for this research work.In this study,guided by the basin-mountain coupling theory,based on sufficient field investigations,the detrital apatite fission track thermochronology is used as the research method,and the thermal history of the basin itself is obtained by simulating the annealed sample particles.Evolution process: The unannealed samples are analyzed for their peak age distribution and characteristics to obtain the major and rapid exhumation periods recorded by the fission track in the source orogen.And determine the provenance area based on the ancient currents.Combining with the results of magnetostratigraphy,structural analysis,paleo-altitude and other results of previous studies,we will reveal the sequence of major tectonic events experienced in the Hoh Xil Basin and its provenance area,and discuss the uplift process of the area since the Paleogene.Initially obtained the following knowledge:(1)Through the analysis of the detrital apatite fission track of 14 samples in the Hoh Xil Basin,it is found that the samples XZ37 and XZ40 located at the bottom of the Erdaogou-Qiaotou section are annealed to form the youngest P1 peak age component(25-20 Ma).The thermal history simulation results of each component of the sample indicate that a rapid exhumation event occurred in the basin at 25-20 Ma.Through the analysis of lag time,track length,and Dpar value,it is found that other samples have not undergone annealing after deposition.The analysis of their age components and lag time reveals that the peak age is divided into two groups from old to new: P3 is 125-103 Ma and P2 is 65-45 Ma,both of which belong to the "moving peaks",indicating that the two During this period,a rapid exposing event occurred in the source area.The signal gradually appeared inflection points around 45 Ma and33 Ma of the stratigraphic age,indicating a major change event in the sediment source area.(2)Based on the study of paleo-currents,combined with the provenance analysis of other previous methods,it is believed that the source of the Corendejia sub-basin in the Eocene was mainly the Qiangtang block on the southern margin of the basin,and it became the East Kunlun orogenic belt in the Oligocene.It is the main provenance;The Tuotuo River sub-basin shows that the provenance area of the Eocene-early Oligocene was distributed in the Tanggula Mountain area,and the main provenance area of the Middle Oligocene-Miocene was the East Kunlun area.(3)There are four periods of major denudation events in the plateau hinterland obtained in this analysis,which occurred at 125-103 Ma,65-45 Ma,33-30 Ma,and25-20 Ma.Based on previous studies,it is found that these rapid exhumation events indicate the tectonic deformation period of the Hoh Xil Basin and its provenance area:the recorded events of 125-103 Ma may reflect the splicing activity of the Lhasa block and the Qiangtang block in the Cretaceous;The 65-45 Ma event is the long-range response of the plateau hinterland to the collision between the Indian and Eurasian continents;the 33-30 Ma event is related to the uplift and expansion of the East Kunlun orogenic belt;the 25-20 Ma event is related to the secondary plateau Uplift related.