西藏甲布钾长花岗岩体地球化学特征及成因

GEOCHEMICAL CHARACTERISTICS AND ORIGINS OF JIABU MOYITE BODY,TIBET

甲布钾长花岗岩体位于西藏措勤盆地中部，出露面积约160km^2，主要由中粗粒、中粒似斑状和细粒似斑状黑云母钾长花岗岩组成．岩石以富硅、钾，贫铁、镁、钙为特征，分异指数（DI）平均达92．71，里特曼指数变化范围在1．22～2．10，ALK平均值为7．5，K2O／Na2O比值均大于1．55，属高钾钙碱性系列花岗岩．稀土及微量元素地球化学特征显示，花岗岩是以壳源为主的壳幔混源型．根据不同测试方法测定岩体同位素年龄在65．1～72．58Ma，属于晚白垩世．

Jiabu moyite body is located in the center of Coqen basin, Tibet, which approximately covers an area of 160 km^2.It is mainly composed of medium grianed to medium - coarse grianed , medium porphyritic and fine-grained porphyritic biotite Moyite. The granites are rich in Si, K and deficient in Fe, Mg, Ca.The average of Differentiation Index is 92.71, with Rittman Index ranging between 1.22 and 2.10,the average of ALK is 7.5 and K2O/Na2O 〉 1.55,which belongs to high-K calcalkaline series. The characteristics of REE and trace elements display that the original magma of the granites is crust-mantle mixtures-mostly coming from crust. With many kinds of testing methods ,we know that the isotopic age is between 65.1 Ma and 72.58 Ma, which belongs to Late Crataceous.