Research Of Ophiolitic Rock In Wunuer Of Yakeshi City In Inner Mongolia Autonomous Region

Wunuer is situated on the eastern segment of Central Asian Orogenic Belt between the Xin an and Eerguna plate.The ophiolite in the study area was intermittently distributed in the area of the Wunuer-sixty-four meters bridge and it was in contact with the surrounding rock or was covered by the Mesozoic and Cenozoic strata.In combination with petrography,rock geochemistry and isotope chronology studies,the ophiolite massifs which include the basalts,gabbro,diabase,augite peridotite or diabase porphyrite dykes and associated radiolarian cherts is complete.The basic rocks exposed a wide range,these profile are relatively complete,part of the gabbro developed the crystal structure.Basalt often closely associated with radiolarian siliceous rocks.the rock assemblages is made up of two parts,which represented the oceanic crust and the residual body of the earth mantle.the augite peridotite produced in diabase in the form of the nticle.The studied area”s sections of the ophiolite suites whose order are similar with oceanic crust are relatively complete.It reflect the existence of oceanic crust in.the studied area.the ophiolitic rock in the studied area can be divided into two types : the first type has the geochemical characteristics of high Ti,low Al,slight loss of LREE,depleted in Na and Ta,positive exception of Pb.is MORB-like type.the second type has the geochemical characteristics of low Ti,high Al,strong enrich of LREE,strongly depleted in Na and Ta,positive exception of Pb.is IAB-like type.the ophiolitic rock which has both of the two geochemical characteristics usually formed in the basin of the back-arc.Through comprehensive regional comparison studies,combined with LA-ICPMS U-Pb zircon U-Pb dating results(426.1±9.3 Ma,428.1±6.5 Ma),it was determined that the ophiolitic melange formed in the Early and Middle Silurzo,and it provide the geochronological basis for the formation and evolution of Wunuer basin of the back-arc.Combined with comprehensive regional data,the tectonic evolution model of the Wunuer-Toudao Bridge collage belt was preliminarily established.