南秦岭白马山岩体Sr、Nd、Pb同位素组成及源区示踪  

The Sr,Nd,Pb Isotopic Compositon and its Implication for the Magmatic Source of the Baimashan Rock Mass,Southern Qinling

作　　者：张永华[1] 王建中[1,2] 钱壮志[2] 徐刚[2] 姜超[2] 

机构地区：[1]武警黄金第五支队,陕西西安710100 [2]长安大学西部矿产资源与地质工程教育部重点实验室,陕西西安710054

出　　处：《黄金科学技术》2015年第5期20-27,共8页Gold Science and Technology

基　　金：中央高校基本科研业务费专项资金"造山带后碰撞伸展背景下的岩浆铜镍硫化物矿床成矿作用"(编号:CHD2011SY014)资助

摘　　要：研究了南秦岭晚三叠世(~200 Ma)7个花岗岩类岩体的Sr、Nd、Pb同位素组成,包括白马山岩体在内的南秦岭花岗岩类以低放射成因Pb同位素组成为特征,初始87Sr/86Sr比值范围为0.70495~0.70908,εNd(t)值变化于-2.40^-8.55之间,Nd同位素模式年龄(TDM)变化于1.2~1.7 Ga之间,从东部到西部,呈现εNd(t)逐渐降低而TDM逐渐增高的变化规律。白马山岩体的初始87Sr/86Sr比值为0.70637,εNd(t)=-6.75,具有较高的TDM值(1.53 Ga),暗示其岩浆源区主要来自于南秦岭的大陆下地壳,岩浆源区以类似南秦岭耀岭河群基性火山岩为主,南秦岭较古老的地壳物质仅有少量参与。基性下地壳增厚,岩石圈地幔拆沉,软流圈上涌,下地壳部分熔融形成有利于铜、金成矿的白马山"C"型埃达克岩。This paper studies Sr,Nd,Pb,isotopic compositions of 7 granitoids from South Qinling,which were all formed about 200 Ma B.P.The results indicate that the granitic rocks including the Baimashan rock mass from the South Qinling are characterized by low radiogenic Pb isotopic composition.Their initial（87^Sr/86^Sr）t ratios range from 0.70495 to 0.70908,εNd（t）values from-2.40 to-8.55,and Nd isotopic model ages（TDM）from 1.2 Ga to 1.7 Ga.their εNd（t）values gradually decrease from east to west,whereas TDMvalues gradualy increase.The Baimashan rock mass has much lower（87^Sr/86^Sr）t（0.70637）,lower εNd（t）（-6.75）and much higher TDM（1.53 Ga）.This study reveals that the magmatic source of the Baimashan rock mass was derived from the deep continental crust.In the magmatic source,basic magmatic material in the crust similar to the Yaolinghe Group basic volcanic rocks in South Qinling,is the major source for the formation of granitoids with less significant old continental crust material.The Baimashan adakite which is in favor of copper and gold mineralization,may resulted from partial melting of mafic lower crust in the thickened lower crust due to the lithospheric delamination and the asthenospheric upwelling,which can provide some clues to the direct copper-gold prospecting.

关 键 词：同位素组成 岩浆源区 基性下地壳 白马山岩体 埃达克岩 南秦岭 

分 类 号：P597[天文地球—地球化学]