Exhumation History And Geological Significance Of The Mesozoic Granites In Yidun Terrane,Southeastern Margin Of The Tibetan Plateau

Located on the southeastern margin of the Tibetan Plateau,the Yidun terrane is a volcanic island arc consisting of the Changtai Arc,the Xiangcheng Arc and the Zhongdian Arc.In recent years,researchers have shifted their focus from studying the interior of the Tibetan Plateau to the eastern and southeastern margins of the Plateau,carried out extensive work on magmatism,tectonic activity,mineral formation and river evolution in the region.However,the systematic research on the Mesozoic granites of the Yidun terrane in the eastern margin of Tibet is relatively lacking,which not only restricts the understanding of the crustal uplift process since the Mesozoic,but also involves the effective development of regional ore prospecting,exploration and evaluation.More importantly,the denudation process of the Yidun terrane is also of great significance for revealing the uplift and expansion of the Tibetan Plateau since the Cenozoic.Based on previous studies,this paper takes the Mesozoic granites of the Yidun terrane as the main research object,and uses zircon U-Pb dating,zircon and apatite(U-Th)/He dating,combined with numerical simulation to determine the diagenetic time of the granite,and inversely the process of cooling and exfoliation of granites was simulated and the preservation mechanism was discussed.With the help of Arc GIS platform,based on the extraction and analysis of geomorphological parameters such as slope,curvature,terrain roughness index,and relative height,the Yidun Terrane and the planation surface on the southeastern margin of the Tibetan Plateau were quantified.Analysis to gain the following knowledge:(1)Based on the fuzzy function,through the analysis and processing of the SRTM DEM with a resolution of 90 m,the four geomorphological parameters of slope,curvature,terrain roughness index and relative height of the planation surface in the southeast margin of the Tibetan Plateau were extracted,and compared with steep mountain ranges and inter-mountain basin,to determine the fuzzy threshold and establish the barbarian affiliation degree.The results show that the planation surface is mainly located in river watersheds,flat uplands above wide valley basins and valley shoulders.(2)The results of zircon U-Pb dating show that the Yidun terrane mainly developed two periods of magmatism,that is,the Late Triassic and the Late Cretaceous.(3)The results of the low temperature thermochronology show that the Mesozoic granites in the Yidun Terrane experienced a denudation stage from rapid cooling to slow cooling: Late Triassic and Late Cretaceous,Late Cretaceous-Eocene,Oligocene-Miocene,Late Miocene-present.Among them,the long-term slow cooling process during the Late Cretaceous implies a tectonic stabilization phase after orogenic extension;during the Oligocene to Miocene period,low elevation and low relief planation surface developed in the area;after the Miocene,they were disintegrated by local tectonic activity and enhanced fluvial denudation;since the Cenozoic,the strong uplift of the Tibetan Plateau has caused the planation surface to be distributed in the current high-altitude areas.(4)The preservation of the two phases of granite in Zhongdian area benefited from the stable tectonic environment during the Late Cretaceous to Miocene period,which was characterized by the development of planation surface.