西藏冈底斯仁布-拉萨一带花岗岩基的地球化学及其意义  

Geochemistry and implication of the Gangdese batholiths from Renbu and Lhasa areas in southern Gangdese,Tibet

作　　者：黄玉[1] 赵志丹[1] 张凤琴 朱弟成[1] 董国臣[1] 周肃[1] 莫宣学[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室中国地质大学地球科学与资源学院,北京100083

出　　处：《岩石学报》2010年第10期3131-3142,共12页Acta Petrologica Sinica

基　　金：国家重点基础研究发展规划项目(2011CB403102;2009CB421002);国家自然科学基金重点项目(40830317);国家自然科学基金项目(40873023;41073013;40973026);教育部新世纪优秀人才支持计划(NCET-10-0711);111计划(B07011);中国地质调查局综合研究项目(1212010610104)资助

摘　　要：冈底斯岩基记录了特提斯洋壳俯冲消减过渡到印度与亚洲大陆碰撞的深部过程,可以反演壳幔相互作用和高原地壳加厚的历史。本文对冈底斯岩基中段的仁布岩体和拉萨岩体进行了系统的元素、Sr-Nd-Pb同位素和锆石SHRIMP U-Pb定年与Hf同位素研究。本文测年结果为82～45Ma,仁布岩体和拉萨岩体年龄为晚白垩纪到早第三纪。岩石为含有辉长质和闪长质包体的中酸性花岗岩类,岩石类型复杂。岩石富集轻稀土元素和大离子亲石元素,稀土元素总量较低,具有高场强元素的负异常;Sr-Nd-Pb同位素成分表明新特提斯洋地幔端元的较大贡献,岩石具有亏损的Nd同位素和年轻的地幔模式年龄(εNd=-1.5～3.3,tDM=0.5～1.2)和较大变化范围的正的锆石Hf同位素成分(>6个ε单位),表明岩石源区中亏损地幔占有较大贡献,冈底斯岩基显示初生地壳特征。本文进一步揭示出,冈底斯岩基中段存在岩浆底侵与岩浆混合作用,大规模的幔源基性岩浆底侵,不仅导致之后经过岩浆混合形成的花岗岩岩基具有初生陆壳成分,同时也是导致冈底斯南部地壳垂向加厚与增生的重要因素。The Gangdese batholiths are the most important record in revealing the crust-mantle reaction and crustal thickening processes corresponding to the Tethyan oceanic curst subduction and collision between Indian and Asian continents. This paper presents the systematic study of elements,Sr-Nd-Pb isotopic and zircon SHRIMP U-Pb dating and Hf isotope results of the Gangdese batholiths in Renbu and Lhasa areas. The batholiths,with the U-Pb age ranges from 82Ma to 45Ma dated in this work,are granitoids that containing gabbroic and dioritic enclaves. The rocks are enriched in light rare earth elements (REE) and large ions lithophile elements,and depleted in high field stretch elements,and have relative lower total REE contents. The Sr-Nd-Pb isotopes show a large contribution of the Neo-Tethys mantle domains,with depleted Nd and young model ages (εNd=-1.5~3.3,tDM=0.5~1.2)and positive,largely varied zircon Hf isotopes (>6 ε units),suggesting the juvenile depleted mantle materials were dominated in the source regions and magma mixing. This study further implies that mafic underplating and magma mixing has played an important role in generating the Gangdese batholiths. The large-scale underplating event was not only responsible for the magma mixing processes,but also for the crustal vertical thickening and growth in southern Gangdese in the Tibetan plateau.

关 键 词：冈底斯岩基 岩浆混合作用 锆石SHRIMP U-PB年龄 Sr-Nd-Pb-Hf同位素 地球化学 

分 类 号：P588.121[天文地球—岩石学]