| 青藏高原中新生代花岗岩Sr、Nd同位素研究 |
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| 引用本文：邱瑞照,邓晋福,周肃,肖庆辉,蔡志勇,刘翠.2003.青藏高原中新生代花岗岩Sr、Nd同位素研究[J].地球学报,24(6):611-617. |
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| 基金项目:国土资源部国际合作与科技司专项计划(200010103)，中国地质调查局地质调查项目(200110200064,200113900018)和(K1.412)，中国地质大学(北京)“岩石圈构造、深部过程及探测技术”教育部重点实验室基金(2003010) |
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| 中文摘要: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(即冈底斯花岗岩北带和南带)与洋壳俯冲有关的燕山晚期花岗岩，具有低^87Sr／^86Sr初始值(小于0．706)、正εNd(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(0．706～0719)，而εNd(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(大于0.720)、古老模式t2DM年龄(1792～2206Ma)和低εNd(t)值(-10．3～-16．3)特征，并与基底岩石的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主要取决于深部部分熔融物质的成分，不同火成岩组合的差异反映了青藏高原岩石圈组成和演化的不均一性。 |
| 中文关键词:Nd-Sr同位素 中新生代花岗岩 物质来源 青藏高原 |
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| Sr-Nd Isotope Studies of Mesozoic-Cenozoic Granites in Qinghai-Tibetan Plateau |
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| Abstract:Mesozoic-Cenozoic magmatic activities are intense in Qinghai-Tibetan plateau. Nd-Sr isotopic compositions of representative granitic plutons in western Qinghai-Tibetan plateau are reported in this paper. Using these data combined with the previous isotopic data of eastern Qinghai-Tibetan plateau,the authors studied Sr-Nd isotopic compositions,material sources and geneses of Mesozoic and Cenozoic granites in Qinghai-Tibetan plateau.The research results indicate that there exist three types of granite in Qinghai-Tibetan plateau. The granites of the late Yanshanian stage, which are distributed along the northern and southern boundaries of Gandes block (i.e., in northern and southern granitic belts of Dangdes) and related to the oceanic crust subduction, have ( 87Sr/ 86Sr)i of 0.7041～0.7064,εNd(t) of +2.5～+5.7 and t DM age of 312～562 Ma,positive εNd, low ( 87Sr/ 86Sr)i ratio and young Nd model ages. All these data suggest that their sources have relatively high contents of mantle-derived components, and that this type of granites might have been melted from the subduction oceanic crust. The granites in the intra-Gangdes block caused by collision of continent and post-collision have ( 87Sr/ 86Sr)i of 0.706～0.719,εNd(t) of -5.3～-8.3 and t DM age of 1 323～1 496 Ma, negative εNd, and relative high ( 87Sr/ 86Sr) i ratio with mid-Proterozoic Nd model ages, suggesting that the granites have a mixed genesis of mantle-derived components and old crustal components in their sources. The relatively small variation range in εNd(t) and t DM age might imply that the granitic isotopic source in Gandes block maintained relative homogenization in a long period. The granites in Himalayan block, where there is no oceanic material to join in the melting and to cause the intra-continental subduction, have ( 87Sr/ 86Sr)i ratio over 0.720,εNd(t) of -10.3～-16.3 and t DM age of 1 792～2 206 Ma, high ( 87Sr/ 86Sr)i ratio, low negative εNd(t) with old Nd isotopic model ages and Sr, Nd isotopic compositions consistent with those of basement rocks, indicating relatively high contents of crustal components in their sources. It is thus concluded that the formation of granitoids and their assemblages depends on the components of deep partial melting materials. |
| keywords:Sr-Nd isotopes Mesozoic and Cenozoic granite material source Qinghai-Tibetan plateau |
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