The Study Of Structural Geology And Chronology In Maanqiao And Shaliangzi Ductile Shear Zone In Middle Shangdan Orogenic Belt

Shangdan Orogenic Belt is the significant boundary in the Qinling Orogenic Belt,which divides the Northern Qinling Belt and the Southern Qinling Belt in Qinling Orogenic Belt.It records the details of subduction,accretion,collision of Shangdan Orogenic Belt.The major component in Shangdan Orogenic Belt is volcanic-sedimentary rock series in lower amphibole facies to greenschist facies with classical ophiolite suite,metamorphic clasolite,metavolcanite and marble.The geochemistry or mechanism of rocks have been studied by numerous of scholars in Shangdan Orogenic Belt,but the deformed characteristics and deformed mechanism have been in question.In this thesis,the geological area is Maanqiao to Shaliangzi ductile shear zone in the middle of Shangdan Orogenic Belt,and the data of structural characteristics,kinematics,microstructural fabric and evolution of Maanqiao-Shaliangzi ductile shear zone is required with the EBSD and 40Ar/39Ar chronology method.Several conclusions are as following:?1?Maanqiao-Shaliangzi ductile shear zone and Shaliangzi ductile shear zone are the southern and northern boundary in fore-arc prism in Shangdan Belt.Both of them are linear belts from east to west,and in similar kinematic characteristics,which are sinistral shear zones.?2?As to Shaliangzi ductile shear zone,the primary minerals are quartz,feldspar and hornblende.The quartz has strongly deformed in the shear zone,which has undulatory extinction,SGR recrystallization and GBM recrystallization.In the feldspar,plastic deformation,and core-mantle structure have been developed.The porphyroblasts has been observed in deformed hornblende.The deformed minerals,assemblage and the recrystallization reflect that the amphibolite facies are in Shaliangzi shear zone.And the quartz c-axis shows rhomb<a>axis slip and prism<a>axis slip system,which represent that the deformation temperature is about 400?.?3?As to Mananqiao ductile shear zone,the primary minerals are quartz,feldspar,biotite and mica.Under the microscope,the quartz has strongly deformed in the shear zone,which has clearly undulatory extinction,BLG recrystallization and minor SGR recrystallization.For the felspar,there are porphyroblasts and brittle fracture and BLG recrystallization.The quartz c-axis show rhomb<a>axis slip and basal<a>axis slip system,which represent that the deformation temperature is not higher than 300?.?4?The vorticity value of Shalingzi ductile shear zone are between 0.83 to 0.99,while the vorticity value of Maanqiao ductile shear zone are between 0.88 to 0.93,both of them are in subsimple shear.Combined the angle of quartz fabric,which means Shaliangzi shear zone is located in the center and Maanqiao shear zone is in the margin of the shear zone.?5?The result of Zircon U-Pb dating method show the weighted average age is 431.9±2.9Ma,which represent the result of collision of Caledonian era and the closure of Shangdan Ocean in 432Ma.The plateau age by ⁴⁰Ar/³⁹Ar dating method is 123.1±0.7Ma and the inverse isochron age is 123.1±0.8Ma,which show the structrual event in Yanshanian era.?6?Au mineral deposit is closely related to shear zone whatever in special shape or the intrusion time of Xianggou granite complex.The plateau age represents the age of shear zone.After shearing,Au mineral deposit has formed.In the process of subduction,collision of Qinling Qrogenic Belt,Shaliangzi shear zone has recorded the details in Late Calidonian era.The temperature has been higher when Shangdan Ocean subducted beneath the North Qinling Belt.But Manqiao ductile shear zone just has recorded the information of Late Indosinian-Yanshannian era,whose deformation temperature is lower than that in Shaliangzi shear zone.Since in Yanshanian era,Manqiao shear zone has been influenced by the weakening of Shangdan Ocean activity and intracontimental evolution,or influenced by Miaolve Ocean about remote effect.