| 青藏高原中新生代花岗岩Sr、Nd同位素研究 |
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| 关键词:Sr-Nd isotopes Mesozoic and Cenozoic granite material source Qinghai-Tibetan plateau |
| 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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| Sr-Nd Isotope Studies of Mesozoic-Cenozoic Granites in Qinghai-Tibetan Plateau |
| 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. |
| QIU Rui-zhao,DENG Jin-fu,ZHOU Su,XIAO Qing-hui,CAI Zhi-yong,LIU Cui.2003.Sr-Nd Isotope Studies of Mesozoic-Cenozoic Granites in Qinghai-Tibetan Plateau[J].Acta Geoscientica Sinica,24(6):611-617. |
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