Petrogenesis And Geological Significance Of The Quxu Complex In Southern Gangdese

The Gangdese belt arised large-scale magmatism during the Eocene period,and a Basic complex dominated by gabbro is developed in the southern magmatic rock zone.There has been some controversy about the rock origin of the magma rocks in the Gangdese belt and the dynamic background of the area.The article select the gabbro and diorite in the Quxu complex as the research object.Conducted field geological surveys,zircon U-Pb chronology analysis,full-rock geochemical analysis and isotope geochemical analysis.The purpose is to determine the formation process of the Quxu complex and provide new evidence for the crustal growth process in this area.The lithology of the Quxu complex is intricacy and diverse,According the result of zircon U-Pb LA-ICP-MS dating,The age of the Quxu complex is about 47-53 Ma,and the zircon in sample have the higher crystallization temperature?>600??.The geochemical characteristics do not show obvious grouping in gabbro and diorite.Generally,these samples have the characteristics of calc-alkaline and quasi-aluminum.In terms of trace elements,all samples are enriched in LREE and the HREE is relatively deficient.Meanwhile,all samples are enriched in LILE such as Ba,K and deficited in HISF such as Th,Nb,Ta,Zr,Hf.The relative depleted Nb and Ti reflect that the Quxu rock mass was formed against the background of the extruded structure.The lower values of(⁸⁷Sr/⁸⁶Sr),positive values of?Nd?t??2.7-5.7?and the values of Mg^#both indicate the characteristics of depleted mantle.However,the enrichment of LREE,Ba,U,K,Sr shows that the magma sourcs has enriched components added.The measured value of zircon Hf isotope indicates that the mantle-derived magma has been contaminated by a certain degree of crustal material during the emplacement process.The characteristics of the depleted in Nb,Ta,Zr,Hf,Ti and the enriched in Sr,Ba,U,and K elements in the trace element data,indicates that the Quxu complex was formed by the intrusion of basic magma during the subduction of the Neo-Tethys slab and was contaminated by crust-derived materials during the later magma positioning.It is preliminarily determined that the formation of the Quxu complex is due to the subduction process of the New Tethys ocean.The Neo-Tethys slab break off,the water-rich fluid or melt separate out from break off slab melts simultaneously with the mantle and the lower crust overlying the eclogite facies.The overlying mantle wedge partially melted to form a large amount of basaltic magma,forming the new crust of Lhasa block.The Indian plate continuously subducted southward,and the basaltic magma emplaced upward,Promote the partial melting of the new lower crust.The partially melted nascent crust and the intrusive basaltic magma emplaced upward through magma mixing and mixed with the upper crust during emplacement,and finally formed the Quxu complex body.