The Geochemical Characteristics And Geological Significance Of Granite In Xiabie Co, Tibet

Xiabie Co is located in the middle western of the Bangonghu-Nujiang suture zone on the Qinghai-Tibet plateau.According to the regional geology survey,we found that different types of granite are developed in a single pluton in this area.In the post-collision phase,extensive magmatic activities would be developed due to the removal of mountain root.In this environment,upwelling of deeper hot mantle material would lead to partial melting of crust in different depth,that's why we could discover the co–development of different types granite in an individual pluton.Though the comprehensive research of Xiabie Co granite samples,can let us have further understanding of the Bangonghu-Nujiang suture zone history.The granites in Xiabie Co can be divided into Hihg-differentiation Granite?HFG?type I granites and type A1 granites.The contentss of SiO₂ in A-type granite are 68.67%-70.32%,the total alkali contentss are 7.83-8.63%,the values of A/CNK are 1.05-1.16,the valuess of A/NK are 1.38-1.51,Al₂O₃ are 14.9%-15.26%,Fe₂O₃^T are 2.68%-3.69%,CaO are 1.62%-1.88%,and the contents of TiO₂ are0.44%-0.62%.Very enrichment of rare earth elements?REE=194.65-263.77PPM,overall daretribution patterns for the right model,?La/Yb?_N=13.88-17.89,?LREE/?HREE=11.08-12.85,medium negative Eu anomaly,enrichment of large ion lithophile elements,poverty in high field strength elements,the Sr abnormal obviously negative;The contents of SiO₂ in high-differentiation type I granite are77.51%to 80.77%,and the total alkali contents are 6.96%to 7.97%,A/CNK are1.09-1.12,A/NK are 1.15-1.17,the contents of Al₂O₃ are 10.79%to 12.56%,Fe₂O₃^T are 0.88%to 1.33%,CaO are 0.22%to 0.30%,and the contents of TiO₂ are0.09%to 0.17%.?REE=103.67-197.55PPM,?La/Yb?_N=3.51-4.45,the Eu are extremely negative anomaly.The age of type I granite is about 120Ma,and that of type A1 granite is about119.7Ma.According to the different diagrams,we believe that type A1 granite is likely to come from a full greywacke region,indicating a relatively shallow depth,while type I high differentiation granite produced by a mafic clay region,indicating a deeper depth.And type A1 is produced by partial melting,while type I is produced by crystallization differentiation.If type A granite and type I granite developed together in a single pluton,which generally is produced in the back-arc or post-collision environment.Therefore,we believe that the Bangonghu-Nujiang ocean had closed in this period?119.7±1.2 Ma?.