Meso-cenozoic Cooling History Of The Western Qinling:Constraints From Low-temperature Termochronology

The Qinling orogenic belt is one of the important geological units in China.Its tectonic position is special and has experienced a complex and long tectonic evolution.Under the unified tectonic background of late Mesozoic to Cenozoic,the West Qinling experienced a series of tectonic deformations.However,the division of the tectonic evolution stage is still unclear.Although the existing data at different locations show that the micro-blocks in the Qinling orogenic belt have undergone different uplift and reentry processes,and there are differences in structural deformation,due to the lack of chronology data,the uplift and reentry time and erosion amount of each micro-block have not been well quantified.In order to study the denudation and cooling history of the West Qinling since the Meso-Cenozoic,this study focuses on the North and South Qinling Block,collected six granite samples from the North and South Qinling massif,dating and inversion simulation by low temperature thermochronology,analyzed the differential uplift between the North and South Qinling blocks and quantified their uplift and exhumation.The tectonic background of different uplift and exhumation stages is also discussed.The results show that the West Qinling orogen has experienced three different stages of rapid cooling in MesoCenozoic,and shows the differential changes of uplift and exhumation of the North and South Qinling Mountains.The intracontinental deformation begins in the south and expands northward in turn.In the first stage,the South Qinling uplifted rapidly due to the clockwise rotation and northward subduction of the Yangtze plate in the late Triassic-early Jurassic(?210-180Ma).In this stage,the cooling rate of the South Qinling was 1.8?/Myr.In the second stage,from late Jurassic to early Cretaceous(?160C-110Ma),the tectonic activity extended northward,the North China plate subducted southward,and the North Qinling began to uplift related to compression and extension,and the uplift rate of 1.4?/Myr,was consistent with the extensive extensional deformation in the eastern China.In the third stage,during the early-Miocene(?20-0Ma),the north and south Qinling experienced rapid uplift,which was interpreted as the escape of Tibet Plateau material to the northeast margin related to the Indo-Asian plate collision,and the unified uplift was accepted in the West Qinling region.in this stage,the uplift rate of the North Qinling is 3.0?/Myr,and the denudation rate of the South Qinling is 1.0?/Myr.The uplift rate of South Qinling is faster in the first two stages,and that of North Qinling is faster in the third stage.In addition,by calculating and comparing the denudation amount of the north and south Qinling samples,the South Qinling uplift and denudation began from 210 Ma,with an average denudation amount of7.42 km,and the North Qinling uplift and denudation since 160 Ma,with an average denudation amount of 8.17 km.Erosion in North Qinling Block is nearly one kilometer more than that in South Qinling Block.Therefore,the intracontinental deformation of the Qinling orogenic belt extends from south to north and the denudation degree of the North Qinling is relatively high.The North and South Qinling were uplifted and exhumed at different times and rates,suggesting that the intracontinental deformation was controlled by per-existing tectonic boundaries.