CHARACTERIZATION OF DEFORMATION AND X-RAY PETROFABRICS IN THE MIDDLE PART OF THE WAHONGSHAN FAULT ZONE, QINGHAI PROVINCE,NORTHWESTERN CHINA

TheWahongshanfaultzoneinQinghaiprovinceisoneofthemostimportantfaultsinwesternChina.Inthispaper,deformationandX-raypetrofabricshavebeenstudiedinthemiddlesegmentofthefault.Theresultsshowthattheformationofthefaultzonescanbedividedintotwomajorstages:ductilesheardeformationstageandbrittledeformationstage.TheearlystageductileshearingleadstotheformationoftheNW-NNWtrendingmylonitezonesalongthefault,whichisintenselycutbythelate-formedbrittlefaults.X-raypetrofabricsofrocksnearthefaultsindicatethatthemineralsinthetectonitesshowagreatdegreeoforientationinthealignment.Thequartz,whichisaveryimportantmineralinthetectonites,isdeformedbybasalfaceglidingornearbasalfacegliding,andsometimesbyprismaticfacesliding,whichindicatesthattherocksaredeformedinepithermaltomesothermalormesothermalenvironment,andthedynamicrecrystallizationalsoplaysanimportantroleintheformationofthequartzalignment.TheresultsalsodemonstratethatplutonsformedintheHercynianandIndosinianstagesshownogreatductiledeformationascanbeseenfromtheX-raypetrofabrics,soitisconcludedthattheserocksareformedaftertheformationoftheductileshearzones.ResultsofStructuraldeformationanalysisandisotopegeochronologicanalysisofsyntectonicmuscoviteindicatethatWahongshanductileshearzonesareformedinthelateSilurianPeriodduringthelateCaledonianstage.