中甸岛弧成矿斑岩的锆石年代学及其意义  

Zircon geochronology and geological implications of ore-bearing porphyries from Zhongdian arc

作　　者：任江波[1,2] 许继峰[1] 陈建林[1] 

机构地区：[1]同位素地球化学国家重点实验室中国科学院广州地球化学研究所,广州510640 [2]中国科学院研究生院,北京100049

出　　处：《岩石学报》2011年第9期2591-2599,共9页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划973项目(2009CB421004);中国科学院创新项目(KZCX2-YW-Q04)联合资助

摘　　要：义敦岛弧南段的中甸岛弧印支期浅成-超浅成斑岩体与成矿密切相关,本文对该地区代表性的成矿斑岩如西侧的雪鸡坪、东侧的欠虽等岩体开展了高精度的LA-ICPMS锆石U-Pb定年,获得雪鸡坪成矿斑岩的年龄为213.4±1.5Ma,欠虽石英闪长玢岩年龄为217.1±1.5Ma。本研究和近几年发表的高精度锆石U-Pb年代学成果发现前人划分的中甸岛弧地区东、西成矿斑岩带的斑岩体形成时代没有明显的差异,这些斑岩体呈面状分布,其形成时代集中在223～211Ma,应该属于同一构造作用的产物。同时,这些成矿斑岩的锆石REE配分模式图显示一致的成分趋势,具有强烈的Ce正异常和相对较低的Eu负异常,指示出岩浆过程具有高的氧逸度。结合它们埃达克质的地球化学研究成果,我们认为中甸岛弧成矿斑岩以及相关的斑岩矿床是在东侧的甘孜-理塘洋晚三叠世俯冲过程中形成的,俯冲板片熔体的参与形成了高氧逸度富金属的岩浆,其对区内成岩和成矿过程具有重要意义。Hypabyssal porphyries associated with porphyry copper deposits are widely distributed in Zhongdian island arc in the northwest of Yunnan Province.The LA-ICPMS zircon U-Pb method is used to date the formational age of the porphyries in western and eastern side of the Zhongdian island arc.Zircons separated from Xuejiping ore-bearing porphyry in the western side of Zhongdian yielded mean 206Pb/238Pb ages of 213.4±1.5Ma.Meanwhile zircons separated from Qiansui quartz dioritic porphyrite in the eastern side of Zhongdian yielded mean 206Pb/238Pb ages of 217.1±1.5Ma.These ages are consistent with those of high-precision zircon geochronology reported by other porphyries in this area,which indicate they are coeval and without obvious different ages between western and eastern side porphyries in the Zhongdian island arc.Together with other published geochronological data,these Indo-porphyries related to mineralization were predominantly formed at 223~211Ma and spatially exhibited a planar-shaped distribution.All of these zircons display the same REE patterns with extremely high CeN/CeN＊ and relatively weak EuN/EuN＊ ratios,which hints that the magma formation experienced a condition of high oxygen fugacity.We suggest that these porphyries related copper deposits are probably related to the westward subduction of the Ganzhi-Litang ocean plate during Late Triassic.The melts from subducted slab with relatively high oxygen fugacity and fertile in metal possibly play an important role in promoting mineralization of the porphyry copper deposits.

关 键 词：LA-ICPMS 氧逸度 中甸岛弧 印支期 

分 类 号：P618.510.5[天文地球—矿床学]