Cenozoic Tectonic Evolution Of The Wuyu Basin In Southern Tibet Based On Fission Track Thermochronology

The collision of the Indian plate and Eurasian plate in Cenozoic led to the deformation and uplift of nearly 2000 kilometers north of the Himalayan orogenic belt,forming the Tibetan Plateau known as the roof of the world which had a deep influence on the landform,environment and tectonics in Asia.So the Tibetan Plateau has become a natural laboratory on the study of continental collision,lithosphere and crustal deformation.However the current study about the process of the Tibetan Plateau uplift and dynamics mechanism which is the core problem is still unclear,so it is necessary to obtain more evidence for the temporal and spatial evolution of tectonic uplift in key areas of the Tibetan Plateau with various research methods.The Wuyu basin in the south of the Tibetan Plateau is located at the junction between the southern margin of the Gangdise tectonic belt and the Yarlung zangbo river suture zone.It is one of the most representative basins formed by the uplift of the Gangdise mountains since the India plate collided with the Eurasian plate.Tectonic evolution in Cenozoic indicates the process of deformation uplift in southern Tibet.A complete Oligocene-Early Pleistocene sedimentary record is kept in the Wuyu basin.These terrigenous detrital sediments not only record the sedimentary evolution information of the basin,but also the tectonic uplift information of the surrounding orogenic belt.The apatite fissiontrack thermal chronology has a lower closure temperature and is sensitive to the shallow tectonic deformation events of the crust.It preseves the denudation and chilling history of carrier rocks in the lower crust.Therefore,this article choose the Wuyu basin in the Cenozoic strata deposits as the research object,the fission-track thermal chronology of detrital apatite is emphasized in the Wuyu basin on the basis of establishing basin stratigraphic sequence and restoring sedimentary evolution process.Meanwhile,we reveal the Cenozoic tectonic deformation events and sedimental-tectonic evolution process combined with previous research results.It provides evidence for further study of the formation process of the Tibetan Plateau,especially the time,process and mechanism of Cenozoic tectonic activity in the southern part of the Tibetan Plateau.This paper mainly obtains the following understandings and conclusions:(1)Through the detrital apatite fission-track thermal chronology analysis in Wuyu basin,the "static peaks" of unannealed detrital apatite fission-track fitting age components were obtained,which ranged from 65.4-51.5,47.5-36.7 and 31.3-22.9 Ma.Among them,the "static peak" of 65.4-51.5 Ma is the cooling signal of Linzizong volcanic rock as well as the magma response product of the initial collision event between the India and Eurasia plate.The "static peak" of 47.5-36.7 Ma represents the rapid cooling and deformation event in the Gangdise tectonic belt during the transition from the plateau to the continental uplift orogenic stage.The "static peak" of 31.3-22.9 Ma represents a strong and rapid uplift,deformation and cooling event in the southern Tibet in the Oligocene,led to the beginning of Cenozoic sedimentation in Wuyu basin.(2)Tectonic and sedimentary evolution since Oligocene in Wuyu basin: Intense tectonic activity in southern plateau in Early Oligocene led to the depression of Wuyu basin,which accepted intermountain basin deposits dominated by pyroclastic and volcanic rocks in Rigongla formation.The Late Oligocene to Early Miocene tectonic activity resulted in the formation of delta-lacustrine-swamp deposits in Mangxiang formation in the fault depression of Wuyu basin.During the Middle Miocene(~15 Ma),tectonic uplift and volcanism transformed the fluvial and lacustrine sediments at the end of the Wuyu basin into continental environments by volcanic rocks and pyroclastic rocks in Laiqing formation.The strong tectonic activity around 8 Ma caused the Wuyu basin to be faulted into lakes again,and formed the fan delta-fluvial-lacustrine-swamp sediments in Wuyu formation.The rapid uplift of regional structure around 2.5 Ma transformed the lacustrine sediments at the end of the basin into the braided fluvial coarse clastic sediments in Dazi formation.(3)According to the comprehensive analysis of contact relationship of Cenozoic strata,sedimentary characteristics,sedimental-tectonic evolution and detrital apatite fission-track thermal chronology in the Wuyu basin,it is revealed that the Cenozoic has experienced six important tectonic deformation uplifting events at 65-52、48-37、31-23、~15、~8 and ~2.5 Ma.