Characteristics And Tectonic Significance Of Nawucuo's Ophiolite In The Western Segment Of Northern Tibet

Based on the geological survey in the field,ophiolite from Nawucuo in the western segment of Bangonghu-Nujiang suture zone were selected for detailed field with characteristics,petrological characteristics,geochemical characteristics,characteristics of rare earth elements and trace elements characteristics ananlysis test,find out the main rock types,combination,Analyzes and discusses the formation and tectonic environment of ophiolite,and discusses formation in the western environment of Bangonghu-Nujiang suture zone.In the research area,ophiolite is mainly sporadically distributed in the eastern of Nawucuo,the northern part of the shenggela and the west of the Saibu,and the exposed area is about 10km2,which is produced in the form of tectonic rock block in the Mugagangri rock Group sandstone or sand slate,which is one of the members of the Nawucuo tectonic melange belt in Bangonghu-Nujiang suture zone.The petrographic and petrographic studies of the ophiolites in the suture zone show that the rocks are mainly serpentine(total eddy pyroxene peridotite),chloritized monolithic pyroxenite,Chlorite feldspar amphibolite,green curtain glitter plagioclase,strongly altered basalt,dyke group,siliceous rocks.The main elements and rare earth elements in the suture zone are characterized by high Cr,Ni,Co,rare earth and low Mg.The characteristics of the main elements and rare earth elements show that they have homogeneous magma with altered basalts.The main element of the altered basalt shows that it has the characteristics of the transition from basaltic basalts to alkaline basalts.The results of trace elements show that it is obviously different from the typical mid-ocean ridge basalts,and the distribution form is almost flat and relatively rich in large ion lithophile Rb,Ra,Sr and high-strength elements Th,Ta,Hf,but Nb loss;in the rare earth element distribution mode for the light rare earth enrichment of the right dip type,no significant Eu anomalies,but negative Ce anomalies,The characteristics of alkaline basalts are similar.According to the geochemical characteristics of ophiolite and thetectonic environment discriminant diagram,it is determined that the ophiolite is formed in the continental ridge expansion environment,but not the typical oval-type ophiolite,similar to the marginal sea-type ophiolite.