藏东波密-察隅地区晚侏罗世花岗岩的成因及构造意义  

Petrogenesis and tectonic significance of the Late Jurassic granite discovered in the Bomi-Chayu region,eastern Tibet

作　　者：李化启[1] 许志琴[1] 王瑞瑞[1] 董汉文[1] 孙载波 黄学猛[1] 

机构地区：[1]中国地质科学院地质研究所,大陆构造与动力学国家重点实验室,北京100037 [2]云南省地质调查院,昆明651000

出　　处：《岩石学报》2013年第6期2024-2032,共9页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(1212010818035);国家自然科学基金创新研究群体项目(40921001);中央级公益性科研院所基本科研业务费项目(J1304、13CX02036A)联合资助

摘　　要：西藏东部的波密-察隅地区是拉萨地体的南东向自然延伸,其中生代以来的演化一直被认为是处于北部的班公湖-怒江洋和南部的雅鲁藏布洋两个动力学系统中。相应地,该区广泛分布的晚中生代-新生代岩浆岩也被认为与两个大洋的发展演化及随后拉萨-羌塘、拉萨-印度的碰撞和后碰撞作用直接相关。本研究在波密-察隅地区中北部的伯舒拉岭岩浆带中发现了晚侏罗世的花岗岩,锆石LA-ICP-MSU-Pb测年表明其形成时代为151～153Ma,地球化学显示较强的δEu负异常,锆石εHf(t)值基本在误差范围内波动,平均值为-7.75和-7.77,表明这期花岗岩为古老地壳重熔的产物,与传统认为的该时期岩浆活动对应怒江洋的俯冲岛弧背景相矛盾。结合该区发现的早侏罗世壳源花岗岩及区域沉积特征,本文认为波密-察隅地区侏罗世的壳源花岗岩应该是拉萨地体内新发现的印支期或早中生代造山事件后地壳增厚或伸展阶段岩浆活动的反映或继续,而和传统认为的怒江洋俯冲没有关系,拉萨地体东部的波密-察隅地区在演化方面可能有其特殊性。有关藏东波密-察隅地区中生代构造演化的研究还需大量地质工作以及多学科的研究去证实。Bomi-Chayu region,of eastern Lhasa terrane between Bangongco-Nujiang and Yarlung Tsangpo sutures,is located east of the Himalayan Syntaxis. Widely distributed magmatite of the Late Mesozoic-Cenozoic in this area is regarded to concern the evolution of Neo-Tethys 0ceans and collisions or post-collision of Lhasa-Qiangtang and Lhasa-India. In this study,the Late Jurassic granite is investigated. Zircon LA-ICP-MS U-Pbdating indicates that the granites were formed at 151～153Ma,with average zircon ε Hf （ t） values of - 7. 75 and - 7. 77. The geochemistry shows strong δEu negative abnormal. All of these features suggest that the Late Jurassic granite should be of crustal source type. In contrary to traditional view,thisdoes not correspond with the island arc background by Nujiangocean subduction. In addition,former studies had presented Early Jurassic crustal source granite and unconformity between Middle Jurassic and underlying strata in this region. Thus,this study suggests that the Jurassic crustal source granite should relate to an uncertain Early Mesozoic tectonic event,but not the Late Jurassic Nujiangocean subduction. The Mesozoic geological evolution of the Bomi-Chayu area may have its particularity in contrast to other part of the Lhasa terrane,which needs further study to confirm.

关 键 词：波密-察隅地区 晚侏罗世 花岗岩 构造意义 

分 类 号：P588.121[天文地球—岩石学] P597.3[天文地球—地质学]