Study On Intermediate-acidic Intrusive Rocks Of Shiquan River Ophiolite Melange Belt In Tibet

As the west part of Shiquan River-Yongzhu-Namucuo-Jiali ophiolitic melange belts,Shiquan River ophiolitic melange belt is located between the AnglonggangriBange magma arc and the Cuoqin-Shenzha magma arc.In this paper,Zizimari granodiorite and Kuerduo diorite as the research object,through the investigation of field geology,petrology,geochemistry and zircon U-Pb chronology analysis test,combined with regional geological data and previous research results,to discuss the tectonic evolution of the Shiquan River ophiolitic melange belt.Petrographic and geochemical analysis showed that the Zizimari granodiorite belongs to the calcareous series and the low potassium series,and the ratio of A / CNK is larger than 1.1,which shows the characteristics of S-type granite.The granodiorite and inclusions belong to calc alkaline series,and the A/CNK ratio is less than 1.1,which shows the characteristics of I type granites.According to the petrology and geochemical analysis of the Zizimari granodiorite and Kuerduo diorite,the two rock masses show the enrichment of LREE and the loss of HREE.The results show that the Zizimari granodiorite and Kuerduo diorite characteristics show that magmatic rocks of island arc type that related to subduction which enriched LREE and enriched in the Rb,K and other LILE elements,depleted Nb,Ta,Ti and other high field strength elements.Combine with Nb/Ta ratios and Rb/Sr ratios and changes of Cr,Ni and Sr content,show that the magma has the characteristics of crust-mantle mixing.Zircon U-Pb age is 166.4±1.8Ma,which represents the Zizimari granodiorite formation age.Zircon U-Pb age is 168.8 ± 1.6Ma,which represents the Kuerduo diorite formation age.In combination with regional geological studies,the ocean basin represented by the Shiquan River ophiolitic melange belt may be in a subduction tectonic environment in middle Jurassic.Combining the regional geological background and predecessors' studying results,Shiquan River ophiolitic melange belt of tectonic attribution to Bangong Lake-Nujiang suture zone south to dive at different stages of island arc and back-arc basin formed during different periods.The tectonic evolution of the Shiquan River ophiolitic melange belt experienced the opening of the Shiquan River ocean basin during the Late Triassic-Early Jurassic.With the formation of Shiquan River area oceanic crust in the early Jurassic,the formation of the Shiquan River ophiolite melange belt arc basin system.In the Middle Jurassic period,parts of Shiquan River by expansion into the subduction,and the south belt in the early of Middle Jurassic was closed,north belt still exists in the subduction of oceanic environment.In the early Cretaceous period,the northern belt inherited part of the south belt,which was connected with the Shiquan River and closed in the late Cretaceous.The late Cretaceous period,Shiquan River basin closed into the intracontinental orogenic stage.From the Paleogene to the Quaternary,it is the India Asia continental collision orogenic evolution stage.