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通过对出露于西藏南部岗巴—定日地区花岗岩体的地球化学研究表明,岩石中SiO2,Al2O3,Na2O和FeO,MgO等的含量均高,贫CaO和Fe2O3;w(SiO2)介于71.40%～73.06%,A/CNK在1.17～1.34之间,为铝和硅过饱和类型的强过铝质花岗岩。岩石的稀土元素总量(ΣREE)为56.80×10-6～89.12×10-6,(La/Yb)N=6.30～18.26,(La/Sm)N=2.62～3.40,ΣLREE/ΣHREE=2.41～4.66;稀土元素配分曲线呈右倾型,具有弱的负铕异常。Nb,Ti等高场强元素具有明显的亏损,而Rb,U,La,Nd,Hf,Eu,Y等大离子亲石元素具有明显的正异常。岩石的87Sr/86Sr初始比值较高,87Sr/86Sr为(0.738 71～0.751 12)。综合研究认为,本区花岗岩的成因为陆壳部分熔融作用形成的,属陆壳改造型强过铝质花岗岩。本区花岗岩岩浆源区岩石成分主要为砂屑岩,其次为泥质岩,是上地壳部分熔融作用的结果。岩石的微量元素标准化曲线图、岩石地R1-R2图解、Rb-(Yb+Ta)和Rb-(Nb+Yb)图解均显示本区岩体形成于同碰撞构造环境的花岗岩,具有同碰撞岩浆活动的特征,是喜马拉雅早期印度板块与冈底斯板块的俯冲碰撞导致的地壳增厚,上地壳部分熔融的产物;为形成于同碰撞构造环境的花岗岩。
The geochemical study of the granite bodies exposed in the Gamba-Dingri area in southern Tibet shows that the contents of SiO2, Al2O3, Na2O, FeO and MgO are all high in the rocks, ranging from 71.40 % ~ 73.06%, A / CNK is between 1.17 and 1.34, which is a strongly over-aluminous granite of aluminum and silicon over-saturation type. The total rare earth elements (ΣREE) of rocks are 56.80 × 10-6 ~ 89.12 × 10-6, (La / Yb) N = 6.30-18.26, La / Sm = 2.62-3.40 and ΣLREE / ΣHREE = 4.66; Rare earth element distribution curve is right-inclined, with weak negative europium anomaly. High field strength elements such as Nb and Ti have significant losses, while large ion lithophile elements such as Rb, U, La, Nd, Hf, Eu and Y have obvious positive anomalies. The initial ratio of 87Sr / 86Sr rock is higher, and the 87Sr / 86Sr is (0.73871 ~ 0.75112). According to the comprehensive study, the genesis of the granites in this area is formed by the partial melting of the continental crust, and is a type of strong over-aluminous granite with the transformation of the continental crust. The rock components of the granite magmatic source area in this area are mainly composed of sandstone rocks, followed by argillaceous rocks, which are the result of partial melting of the upper crust. The standard curves of trace elements in rocks, the R1-R2 diagram, the Rb- (Yb + Ta) and the Rb- (Nb + Yb) diagrams show that the rock mass of this area is formed in the granite with the same collision structure and has the same collision magma The characteristics of the activity are the thickening of the crust and the partial melting of the upper crust caused by the subduction collision of the early Himalayan plate with the Gangdise plate; granites formed in the same collision structure.