西昆仑库地岩组地质特征及形成时代

The Geological Characteristics and Formation Epoch of West Kunlun Kudi Petrofabric

库地岩组主要分布于塔里木板块西南缘西昆仑中间地块西河休-帕合堡一带，主要为枕状构造的杏仁状玄武岩、粗玄岩。玄武岩SiO2含量为47．39％～53．91％，岩石碱值（A．R）为1．13～1．40，K2O／Na2O为0．01-0．08，里特曼组合指数（σ）为0．54～1．88，Na2O—2〉K2O，镁铁含量为16．89％-21．07％，属钠质高镁、高铁拉斑玄武岩。稀总姓低，略具铕正异常，（La／Yb）N=1．38～2．36．属轻稀土富集刑。稀土分馏不明显，为深源措浆演化产物，是库地蛇绿岩重要组成部分。本次研究存库地岩组玄武岩源产物辉长辉绿岩中首次获得U—Ph锆石年龄为（524．2±2．4）Ma，时代为早寒武世，为库地蛇绿岩形成演化提供了重要时代依据。

Kudi petrofabric is mainly located in the Xihexiu-Pahepu region,the middle plots of the western Kunlun in the southwestern area of Xinjiang tarim plate, this pillow-structure petrofabric mainly develops almond-shaped basalt and dol- erite.The content of SiO： in basalt ranges from 47.39% to 53.91%, the rock base number（A.R） ranges froml.13 to 1.40, the ratio of K20/Na20 ranges from 0.01 to 0.08, Rittman combination index （σ）） ranges from 0.54 to 1.88,Na：O-2〉 K.,O, the mafic and iron element content ranges from 16.89% to 21.07%, which leads to the conclusion that the rock is sodic high iron,high magnesium tholeiite pattern.The content of REE is low and a slightly normal anomaly,（LaJYb）N= 1.38 - 2.36, the rock is abundant in LREE;and the fractionation of LREE is not obvious,which means the rock is the product of a deep source of magma evolution,meanwhile it is an important component of the Kudi petrofahric.This paper makes the discovery that the U-Pb zircon age is value of （524.2 ±2.4） Ma for the first time from the gabbro diabase which is the ho- mologous product with basalt,and its epoch is the early Cambrian,which provides an important era basis for formation and evolution for the Kudi ophiolite.