Characteristics Of Mesozoic Thrust-Nappe Structures In The Adjacent Area Of Anhui,Zhejiang And Jiangxi Provinces

During Mesozoic,under the influences of the Indosinian Orogeny and the Yanshan Orogeny,the adjacent area of Anhui,Zhejiang and Jiangxi provinces had many tectonic activities and formed many thrust-nappe structures.However,studies with comparisons,analyses and stage-divisions for the entire area are insufficient.Based on the problem,this research investigates and analyzes the manifestation,age and mechanism of Mesozoic thrust-nappe events in the study area.Through field work,collecting,reading,and sorting data,based primarily on the age of formation of strata and magmatic rocks affected by thrust-nappe structures,it is believed that there are three stages of thrust-nappe events in the research area: in the Middle Triassic,the Late Jurassic,and the Late Cretaceous.The thrust-nappe structures formed in the Middle Triassic are mainly in the northwestern Zhejiang province where is in the eastern part of the research area.The event affected the Lower Triassic and previous strata.The thrusts are mainly trending to the northeast,dipping to the southeast and moving to northwest.Their deformations are weakened to the northwest.This event is not clear in the western and central parts of our research area.The thrust-nappe structures formed in Late Jurassic are observable on the margins of the Mesozoic basins with red sedimentary around Huangshan City and the Taqian-Fuchun thrust belt in the west.This event affected the Middle Jurassic and earlier strata.The strike of the thrusts is mainly the northeast or north-north-east.In the southeast area,thrusts were moving to northwest.But in the northwest,they were moving to southeast.Here formed a hedging structure.This thrust-nappe event had a great influence on magma and metallogenic activities in this area.Many thrusts became channels of magma or ore-conducting structures.The thrust-nappe structures formed in Late Cretaceous are obvious in Shexian,Jixi and some other places in the eastern part of our research area.Nappes covered the Cretaceous strata of red clastic rocks.The strike of these thrusts is mainly north-north-east,and most of them are dipping to south-south-east,moving to north-north-east.Some thrusts are reactivation of pre-existing thrusts.During Mesozoic,South China experienced major tectonic events such as the Indosinian Orogeny,the Yanshan Orogeny and the transition from the Tethys tectonic domain to the Paleopacific tectonic domain.A comprehensive analysis shows that the thrust-nappe structures formed in the Middle Triassic in the area are mainly related to the extrusion between the Indochina,South China and North China blocks.While the thrust-nappe structures formed in the Late Jurassic and the Late Cretaceous are related to the subduction of the Paleopacific plate.Changes of the direction and the angle of plate subduction made the tectonic setting in the Late Mesozoic in this area more complex and variable.The igneous rocks,sedimentary basins,normal faults and strike-slip faults in the area recorded the history of these changes.Moreover,regional geological conditions also played important roles in the tectonic deformations.They influenced the attitudes of the faults and allowed the reactivation of pre-existing faults.The study of Mesozoic thrust-nappe structures in the adjacent area of Anhui,Zhejiang and Jiangxi provinces,the existing research gaps have been littlely made up.The research is also helpful for finding deposits and analysis of mineralization in this area.The study can also provide materials for more large-scale research on Mesozoic geological history and evolution.