The Asymmetric Model Of Temporal And Spatial Magma-tectonics Evolution In Early Paleozoic In Western Chinese Central Tianshan,Xinjiang

Chinese Central Tianshan is one of the important parts of Central Asian Orogenic Belt in China.It experienced the subduction and collison of Terskey Ocean and South Tianshan Ocean in Early Palaeozoic,along with much magmatic rocks.Several researchers have noticed the asymmetric magmatic and tectonic evolution model in Early Paleozoic in Chinese Central Tianshan.However,it is still indefinite about what kind of asymmetric model in this zone.The research was done about magmatic rocks in several sites in western part Chinese Central Tianshan.The data collected in this paper with data from literature were analysed and then some conclusions werer gotten in this paper.The Terskey Ocean in China has been opened in Early Cambrian.Zircon U-Pb age of gabbrodiorite in Xiatebulak ductile shear belt is 515Ma.Geochemical analyses of gabbrodiorite show A/CNK=0.99¹.05.The chondrite-nomalized REE pattern of gabbrodiorite shows flattened model and weak negative Eu anomalies.The gabbrodiorite are rich in Ba,U and infertile in Th,Nb,Nd and Zr.The gabbrodiorite which has feature of MORB may belong to fragments of Terskey Ocean.As southern sunduction of Terskey Ocean in China in Early Paleozoic,there are monzogranite and quartz diorite developed in the Buheta mineralization district.The LA-ICP-MS zircon U-Pb dating results of monzogranite and quartz diorite yielded 434Ma and 445 Ma.According to geochemical data,the granites are ascribed to shoshonitic with peraluminous S-type granite with a magma source of meta-greywacke.The zircon U-Pb ages of granite in Kalagailei are 426⁴16Ma.The granites in Kalagailei have a geochemical feature of S-type granite,which was derived from the re-melting of metasandstone and metapelites.It is concluded that the emplacement of granites in Buheta and Kalagailei mineralization district was related to post collison stage of the Central Tianshan Plate and the Yili Plate through partial melting of middle and lower crustal sedimentary rocks.In early age of the Early Peaoloic,the Southern Tianshan Ocean has been subducted in Chinesse Central Tianshan block.There are much Late Ordovician to Early Silurian magmatic volcanic activities in Dundegule tectonic belt with the zircon U-Pb age of 450⁴44Ma.The LA-ICP-MS zircon U-Pb ages of rhyolite,andesite and felsite in Kalagailei deposit is between 451Ma and 437Ma.Geochemical analysis shows that the volcanic rocks are high in K₂O and Al₂O₃ and belongs to a sub-alkaline series.In the spider diagram,they show enrichment in Ba?Tu and U,and depletion in Ta?Nb and Sr..It is suggested that the magmatic rocks in Kalagailei formed at the northern subduction of the South Tianshan Ocean in Early Paleozoic with accreting magmaic arc.There are subduction and collison of Terskey Ocean?515⁴16Ma?and another subduction of South Tianshan Ocean?451⁴43Ma?.Based on geochemistry and chronology of magmatic rock in Chinese Central Tianhan in Early Peaoloic,there is a asymmetric evolution model in Chinese Central Tianshan that the subduction of Terskey Ocean was got younger in eastern part of Chinese Central Tianshan,also the collison of Terskey Ocean and the subducwas got younger begun in weartern part of,also the collison of Terskey.the Ba/Th and U/Th value of magmatic rock related to Southern Tianshan Ocean are increased with time-evolution.It is considered that the contribution of subducted plate fluid is added with grade of subduction.The Th/Nb and Th/La value of magmatic rock in Chinese Central Tianshan are increased with time-evolution,as the partial melting of sediments in magma source region is added in subduction and collison process.