Late Jurassic Erosion In Early Daytime In Tibet-early Cretaceous Tectonic Magma

The study area is located in the middle south of the eastern section of the Gangdese block in the Tethyan structural region in Tibet,and the eastern section of the Gangdise arc back-off belt.Due to the high altitude of the work area and the weak geological work,although some studies have been made on the study of tectonic-magmatic evolution in this area,it is necessary to supplement and further study.This paper focuses on the intrusive rocks of the Late Jurassic-Early Cretaceous in the Tibet Seriong area,mainly based on rock geochemistry,combined with regional geology,petrology,rock composition,zircon U-Pb dating,and the geotectonic theory to study.Dividing its rock unit and its super unit,determining the formation of the age,identifying the cause of the rock and tectonic settings and exploring tectono-magmatic evolution.The following progresses and preliminary understandings have been obtained by studying the tectonic evolution of the Early Cretaceous in the Late Jurassic in the Serirong region of Tibet:The Late Jurassic-Early Cretaceous magmatic rocks in the study area were divided into three units: Cuijueguo,Hankuangda,and Jiaseerzi.The Cuijueguo unit is located in the middle of the study area,emplacement age is 139-142Ma(Late Jurassic),expressed as the evolution of K-feldspar granite ? Alkali feldspar granite;Hankongda units are distributed in the middle of the study area,the emplacement age is 132-136 Ma(Late Jurassic-Early Cretaceous),expressed as the evolution of monzonite granites ? K-feldspar granite;The Gastrell unit is located in the northern part of the study area and the emplacement age is 117-132 Ma(early Cretaceous),expressed as the evolution of monzonite granites ? K-feldspar granite? Alkali feldspar granite.The chemical characteristics of rocks are all characterized by high-separation strong peraluminous high-potassium calcium alkaline S-type granite.The source area is dominated by argillaceous rocks and a small amount of sandy rocks.According to the relationship between tectonic deformation and magma coupling and the tectonics background of magmatic rocks,determined the deep geodynamic processes of the Late Jurassic-Early Cretaceous in the study area.In the late Jurassic,southwards descent from the Bangonghu-Nujiang Tethys Ocean film was detached,upwelling of Asthenosphere,the Gangdese block was began to expand from compression,partial melting of the upper crust argillaceous rocks was induced and strong peraluminous granite was formed.In the early stage of extrusion stress,strong peraluminous granites actively invaded folds formed at the same time,with the development of brittle-ductile shear structure,at this time,the strong peraluminous granite(Cuijueguo unit and hankongda unit)also undergone ductile deformation.Afterwards,the regional stress becomes extension,The ductile shearing motion is over,strong peraluminous granites gradually migrated northwards(Jiaseerzi unit),and are passively located in the regional extensional structure.Late Jurassic-Early Cretaceous strong peraluminous granites in the study area reflecte the Bangonghu-Nujiang Tethys ocean plate was separated and sank,under the stretching stress after extrusion uplift,the mantle of lithosphere happened to upwelling,resulting in the magma reduced in the lithosphere.