Petrogenesis And Tectonic Significance Of Granitic Pluton And MMEs In The Eastern Segment Of The Tiekelike,NW China

The Tarim block has been playing the role of the northern continental crust in the ocean-land transformation process of the West Kunlun orogenic belt.The Tiekelike tectonic belt crosses the Tarim plate and the West Kunlun orogenic belt on the geodetic structure.The properties,boundary and collision and integration history of the two major tectonic units are important scientific problems in the study of the basic geological study in the study area.It is of great scientific significance for understanding the evolution history of the southern Tarim and the West Kunlun Mountains.The early Palaeozoic granites are widely exposed in the eastern section of Tikelike,which record a lot of information about hyperplastic orogeny and crustal evolution.In the paper,author presents petrography,whole-rock geochemistry,zircon U-Pb geochronology and Hf isotopic compositons for the granitoids and its mafic microgranular enclaves from the representative Tiekelike pluton and the Buya plutons,and ascertain their petrogenesis and source area,diagenetic tectonic environment,which provide useful information for studying the way of convergence and hyperplastic orogeny in the West Kunlun orogenic belt.To achieve the main research results are as follows:?1?LA-ICP-MS Zircon U-Pb dating of two representative granitic plutons in the eastern section of Tiekelike in the southern margin of Tarim reveals a late Ordovician-Early Silurian magmatism.For the first time,we got the age of emplacement crystallization of 444.4 Ma in the Tiekelike rocks which indicates that it is formed in the late Ordovician.The age of the BuYa Pluton and its MMEs are 432.4 Ma,respectively,and the formation age of the two is the same,indicating it is formed in the early Silurian.The results of Lu-Hf isotope analysis show that the value of ¹⁷⁶Hf/¹⁷⁷Hf and epsilon Hf?t?of the zircon in the Tiekelike granodiorite are between 0.282397⁰.282497 and-3.7⁺0.1,T²_DM=1418¹643Ma,respectively,and the value of 176Hf/177Hf and epsilon Hf?t?of the zircon in the monzodiorite are between0.281983⁰.282338 and-10.9^-5.7,T²_DM=1778²100Ma,respectively;The value of¹⁷⁶Hf/¹⁷⁷Hf and epsilon Hf?t?of the zircon in the MMEs are between 0.282121⁰.282391 and-13.5^-3.9,T²_DM=1663²263Ma,respectively.?2?Tiekelike Pluton and Buya Pluton have higher Al₂O₃,SiO₂,Na₂O,K₂O and lower TiO₂,MgO and Fe₂O₃^T.They belong to quasi-aluminum type-I granitoids.At the same time,both of them with the characteristics of high Sr and Sr/Y and?La/Yb?_N ratio,lower Y and Yb show HREE and HFSE loss,LREE and LILE enrichment,as well as weak Eu anomalies in the trace element distribution diagrams which have the characteristics of adakites thickening of the lower crust.The two rocks are rich in MMEs,indicating the existence of crust and mantle magma mixing.Combined with petrology,geochemistry and isotopic chronology,it indicates that both of them are rich Na,K C-type adakites with mantle derived magmatism in the Palaeoproterozoic basaltic lower crust and partially fused by the amphibolite and eclogite facies.?3?Late Ordovician-Early Silurian,theTiekelike area on the southern edge of Tarim is an active continental margin arc environment,granitic rocks are widely developed and magma mixing is significant,indicating that the northern Kunlun ocean is not dead and still subducted to the southern margin of the Tarim plate.The Tikelike Pluton and the Buya Pluton are likely to be the late stages of subduction and subduction of the oceanic crust before the continental collision.The continuous subduction and subduction of the northern Kunlun ocean causes a strong crust mantle magma mixing in the subducted subducted and active continental margins.The basaltic rocks of the paleo Mesoproterozoic lower crustal rocks in the lower part of the northern margin of the active continental margin of the northern margin of the active continental margin from the soft asthenosphere invade the lower part of the active continental margin of the northern margin,making it partially melted under the amphibolite and eclogite facies and forming a mixture of rich Na,K adecitic crust and mantle mixed source magma and invaded to the upper crust.