西藏鸡公村钼矿区中酸性岩体的时代、岩石地球化学特征及构造背景  

Geochronology, rock geochemistry and tectonic setting of intermediate-acid intrusive rocks from the Jigongcun molybdenum mining area, Tibet

作　　者：王健[1] 魏启荣[1] 次琼 郑秋平 王旭东 吉雪峰 许欢 WANG Jian;WEI Qirong;CI Qiong;ZHENG Qiuping;WANG Xudong;JI Xuefeng;XU Huan(Faculty of Earth Resources,China University of Geosciences(Wuhan),Wuhan 430074,China;Second Geological Survey,Tibet Institute of Geological Survey,Lhasa 850000,China)

机构地区：[1]中国地质大学(武汉)资源学院,湖北武汉430074 [2]西藏自治区地质调查院二分院,西藏拉萨850000

出　　处：《地学前缘》2018年第6期152-164,共13页Earth Science Frontiers

基　　金：中国地质调查局项目“冈底斯—喜马拉雅铜矿资源基地调查”(DD20160015)

摘　　要：鸡公村钼矿位于冈底斯下察隅晚燕山-喜山期岩浆弧带南缘。文中以矿区广泛分布的中酸性岩体为研究对象,从野外地质调查、岩石学、LA-ICP-MS锆石U-Pb定年、岩石地球化学成分特征等方面对其进行了系统的探讨。研究结果显示:鸡公村中酸性岩体的岩石类型主要为石英闪长岩和少量的花岗闪长岩;中酸性岩体的LA-ICP-MS锆石U-Pb年龄为(51.8±0.5) Ma,表明其形成于始新世(E2)时期;中酸性岩具低K(w(K2O)为1.66%-2.44%)、高Na(w(Na2O)为3.58%-4.06%)的特点,属钙碱性高钾钙碱性系列,具准铝质弱过铝质的特征;稀土总量(ΣREE)变化范围较大((53.6-117)×10^-6),稀土元素配分模式表现为轻稀土富集的右倾斜型,其(La/Yb)N值为3.90-7.31,铈、铕异常不明显(Ce/Ce^*=0.92-1.17,Eu/Eu^*=0.96-1.15);微量元素比值蛛网图上显示出Rb、Th、U、K等元素的正异常和Ba、Nb、Ta、P、Ti等元素的负异常;鸡公村中酸性岩属I型花岗岩,是变玄武岩质下地壳部分熔融的产物;鸡公村中酸性岩体形成于印度欧亚板块俯冲碰撞环境,起源于地壳加厚导致的源区物质的部分熔融。The Jigongcun molybdenum mine is located in the southern part of the Gangdise-Xiachayu late Yanshan-Himalaya magmatic arc zone.In this paper,we studied the intermediate-acid rocks widely distributed in the mining area and carried out a systematic investigation on field geological survey,petrology,LA-ICPMS zircon U-Pb dating and geochemical characteristics of these rocks.The findings indicate that the Jigongcun intermediate-acid rocks are mainly quartz diorite and some granodiorite.The rocks’ LA-ICP-MS zircon U-Pb age of 51.8±0.5 Ma suggests they were formed in the Eocene (E2) period.They have low K (K2O content ranges 1.66%-2.44%) and high Na (Na2O content ranges 3.58%-4.06%) contents and belong to calc-alkaline-high potassium calc-alkaline series with quasi-aluminum-weak aluminous characteristics.The ΣREE contents vary greatly (53.6-117)×10-6 with light REE enrichment,represented by right-inclined REE distribution mode,and (La/Yb)N value of 3.90-7.31.No obvious Ce and Eu anomalies were observed(Ce/Ce*=0.92-1.17;Eu/Eu*=0.96-1.15),while the trace-element spider diagram shows positive Rb,Th,U and K and negative Ba,Nb,Ta,P and Ti anomalies.The Jigongcun intermediate-acid rocks belong to Itype granite,and formed from the partial melting of the lower basaltic crust due to thickening of the crust,in the subduction and collision environment of the Indo-Eurasian plate.

关 键 词：中酸性侵入岩 锆石U-PB年龄 岩石地球化学 构造背景 鸡公村钼矿 西藏 

分 类 号：P588.121[天文地球—岩石学] P588.122[天文地球—地质学]