西藏拉萨地体南部晚白垩纪石榴石二辉麻粒岩的发现及其构造意义  

Discovery of Late Cretaceous garnet two-pyroxene granulite in the southern Lhasa terrane, Tibet and its tectonic significances.

作　　者：王金丽[1] 张泽明[1] 董昕[1] 刘峰[2] 于飞[2] 王伟[2] 徐方建[3] 沈昆[4] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]中国地质大学(武汉)地球科学学院,武汉430074 [3]中国科学院海洋研究所海洋地质与环境重点实验室,青岛266071 [4]山东省地质科学实验研究院,济南250013

出　　处：《岩石学报》2009年第7期1695-1706,共12页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查工作项目(1212010918012);国家自然科学基金项目(40772049);中国地质大学地质过程与矿产资源国家重点实验室开放基金项目(GPMR2009-7)资助

摘　　要：拉萨地体位于青藏高原南部,其中-新生代构造演化过程与新特提斯洋的俯冲、消亡和印度与欧亚大陆的碰撞密切相关,是揭示青藏高原形成与演化历史的关键之一。本文报道了在拉萨地体东南部林芝岩群中发现的石榴石二辉麻粒岩。这种岩石的共生矿物为石榴石、单斜辉石、斜方辉石、拉长石、富钛角闪石和黑云母,其原岩相当于基性岩,变质作用的温压条件为T=747～834℃和P=0.90～1.35GPa,形成深度可达45km。与麻粒岩伴生的石榴石斜长角闪岩和大理岩中锆石的U-Pb定年研究表明,它们的变质作用发生在85～90Ma。结合在林芝岩群中广泛发育的同时代岩浆作用和区域变质作用,我们认为拉萨地体南部在晚中生代发生了强烈的安第斯型造山作用。The Lhasa terrane, located between the Bangonghu-Nujiang suture zone and the Indus-Yalung Tsangpo suture zone in the southern Tibetan Plateau, was considered previously as a Precambrian continental block. Mesozoic and Cenozoic tectonic evolution of the Lhasa terrane is closely related to the subduction of the Tethys ocean and the collision between the Indian and European continents; so it is one of the keys to reveal the formation and evolution of the Tibetan plateau. The garnet two-pyroxene granulite which was found at the Nyingtri rock group of the southeastern Lhasa terrene consists of garnet, clinopyroxene, orthopyroxene, labradorite, Ti-rich amphibolite and biotite, with a chemical composition of mafic rock. The metamorphic conditions were estimated to be at T = 747 similar to 834 degrees C and P = 0.90 similar to 1.35GPa, suggesting a formation depth of 45km. The zircon U-Pb dating for the garnet amphibolite and marble associated with the granulite give a metamorphic age of 85 similar to 90Ma. This granulite-facies metamorphic event together with a contemporaneous magmatism demonstrated that the southern Lhasa terrane has undergone an Andean-type orogeny at Late Mesozoic time.

关 键 词：麻粒岩 安第斯型造山 晚白奎纪 拉萨地体 青藏高原 

分 类 号：P588.34[天文地球—岩石学] P597.3[天文地球—地质学]