【作者】 邱瑞照； 邓晋福； 周肃； 肖庆辉； 蔡志勇；

【Author】 QIU Ruizhao DENG Jinfu, ZHOU Su, XIAO Qinghui, CAi Zhiyong (Institute of geology, Chinese Academy of geological Sciences, Beijing 100037; China University of geosciences, Beijing 100083; Yichang institute of geology and mineral resources, Yichang 443003; Information Center of Ministry of Land and Resources, Beijing 100812; Exibei institute of geology and mineral resources, Hubei geoexploration bureau, Xiangfan 441003)

【机构】 中国地质科学院地质研究所； 中国地质大学； 国土资源部信息中心； 湖北地质勘察局鄂西北地质矿产研究所；

【摘要】 青藏高原中新生代岩浆活动强烈,本文报道青藏高原西部中新生代代表性花岗岩的Sr,Nd同位素测定结果,结合前人已发表的东部地区花岗岩同位素资料,初步探讨了青藏高原地区中新生代花岗岩的Sr,Nd同位素组成、物质来源与成因。研究表明,分布于冈底斯地块北南边界（即冈底斯北带和南带）与洋壳俯冲有关的燕山晚期花岗岩,具有低⁸⁷Sr/⁸⁶Sr初始值（<0.706）、正ε（Nd）t值和年轻的T2DM模式年龄的特征,岩浆来源于俯冲洋壳的熔融;与陆-陆碰撞及碰撞后有关的冈底斯花岗岩⁸⁷Sr/⁸⁶Sr初始值变化大（0.706～0.719）,而ε（Nd）t值和T2DM都在很小范围变化,Sr、Nd同位素组成似乎与时代、岩性无关,说明壳幔混合花岗岩的同位素源区长时期保持相对均一。无洋壳物质参与的通过陆内俯冲作用形成的喜马拉雅区花岗岩,具有高⁸⁷Sr/⁸⁶Sr初始值（>0.720）、古老模式T2DM年龄（1792～2206Ma）和低ε（Nd）t值（-10.3～-16.3）特征,具有与基底岩石的Sr,Nd组成一致,岩浆源区为壳源。由此说明花岗岩类及其岩石组合的形成决于深部部分熔融物质的成分。更多还原

【Abstract】 Mesozoic-Cenozoic magmatic activities were intensive in Qinghai-Tibetan plateau. Nd-Sr isotopic compositions of representative granitic plutons in western Qinghai-Tibetan plateau are reported in this paper. Combining with past isotopic data, which has reported in eastern Qinghai-Tibetan plateau, Sr-Nd isotopic compositions and material source and genesis of Mesozoic and Cenozoic granites in Qinghai-Tibetan plateau have been studied. The research result indicates there are three types of granite existing in Qinghai-Tibetan plateau, the granites of Late stage of Yanshan Period which distributing on north and south boundary of Gandes block( namely in north and south granitic belts of Dangdes) and cause of oceanic crust subduction, have (87Sr/86Sr)i of 0.7041 ～ 0.7064, ε (Nd) t of +2.5 ～ +5.7 and TDM age of 312 -562Ma, positive ε Nd, low (87Sr/86Sr)i ratio and young Nd model ages suggest relatively high contents of mantle-derived components in their sources, and this type granite might melt from subduction oceanic crust. The granites occurred intra-Gangdes block which were caused by collision of continent and post-collision, have (87Sr/86Sr)i of 0.706 ～ 0.719, ε (Nd) t of-5.3 ～ -8.3 and TDM age of 1323 ～ 1496Ma, negative e Nd, relative high (87Sr/86Sr)i ratio with an mid-Proterozoic Nd model ages, suggest granite has the mixing genesis of mantle-derived components and old crustal components in their sources. With relatively small variation range in ε (Nd) t and TDM age, it might imply granitic isotopic source in Gandes block to keep relative homogenization in long period. The granites in Himalayan block which there is not oceanic material to join in melting and to cause of intra-continental subduction, has most (87Sr/86Sr)i ratio more than 0.720, ε (Nd) t of -10.3 ～ -16.3 and TDM age of 1792 ～ 2206Ma, high (87Sr/86Sr)i ratio, low negative ε (Nd)t with old Nd isotopic model ages and consistent with the Sr, Nd isotopic compositions of basement rocks, indicating relatively high contents of crustal components in their sources. It’s concluded that granitoids and their assemblage lie on the components of deep partial melting material.更多还原