| 西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束 |
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| 引用本文： | 曲晓明,辛洪波,杜德道,陈华.西藏班公湖-怒江缝合带中段碰撞后A型花岗岩的时代及其对洋盆闭合时间的约束[J].地球化学,2012(1):1-14. |
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| 作者姓名： | 曲晓明 辛洪波 杜德道 陈华 |
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| 作者单位： | 中国地质科学院矿产资源研究朊国土资源部成矿作用与资源评价重点实验室,北京100037 |
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| 基金项目： | 国家科技支撑计划项目（2006BAB01A05）;中国地质调查局青藏专项（1212010818097） |
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| 摘 要： | 近年来地质调查在班公湖-怒江缝合带中段发现了一批A型花岗岩,岩体呈面积不大(＜1 km2)的岩株产出,岩性上分为钾长花岗岩和花岗闪长斑岩两种,侵入白垩系地层中.岩石化学上这些A型花岗岩相对富硅,SiO2含量在68.62％～75.36％之间,全碱含量(K2O+Na2O=8.03％ ～ 9.37％)和全铁含量(FeO(T)...
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| 关 键 词： | A型花岗岩 锆石U-Pb LA-ICP-MS年龄 岩石地球化学 洋盆闭合 班公湖-怒江缝合带 青藏高原 |
Ages of post-collisional A-type granite and constraints on the closure of the oceanic basin in the middle segment of the Bangonghu-Nujiang suture, the Tibetan plateau |
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| QU Xiao-ming,XIN Hong-bo,DU De-dao and CHEN Hua.Ages of post-collisional A-type granite and constraints on the closure of the oceanic basin in the middle segment of the Bangonghu-Nujiang suture, the Tibetan plateau[J].Geochimica,2012(1):1-14. |
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| Authors: | QU Xiao-ming XIN Hong-bo DU De-dao and CHEN Hua |
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| Institution: | (Key Laborcgory of Meietallogergy and Mineral Resource Assessment, Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037) |
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| Abstract: | A group of A-type granite has been found in recent years in the middle segment of the Bangonghu-Nujiang suture. These granite bodies occur as stocks with exposed areas of less than 1 km2. Lithologically, these A-type granites include two types of biotite granite and granodiorite porphyry, which intrude into Cretaceous sedimentary rocks. Petrogeochemically the A-type granites have high SiO2 contents, varying from 68.62% 75.36%, relatively high FeOT（0.86% 5.39%） and low A1203 （12.76% 15.54%） contents, displaying weak peraluminous and metaluminous characteristics. Trace element N-MORB-normalized spider diagram displays apparent enrichments of large ion lithophile elements （LILE） Rb, Th, U, K, Pb with Ba and Sr of marked depletions. High field strength elements （HFSE） Nb, Ta and Ti are sharply depleted with relative enrichments of Zr and Hf. All of these are characteristics of A-type granite, which are different from arc granite. These granites have high REE contents （∑REE 122 291 μg/g with an average of 201 μg/g）. Light REE are rich relative to heavy REE （LREE/HREE 4.89 9.58, with an average of 5.93） and negative Eu anomalies are sharp （δEu 0.14 0.54,with a mean value of 0.34）, with slightly right-dipping V-type chondrite-normalized rare earth element patterns. Zircon U-Pb LA-ICP-MS dating for the three granite bodies yielded weighted mean ages of （109.6±1.4） Ma （MSWD 3.7）, （112.2±0.9） Ma （MSWD=0.06） and （113.7±0.5） Ma （MSWD 0.21）, respectively, and indicates that they formed in the late stage of the Early Cretaceous. From their zircon U-Pb ages and post-collisional A2-type signatures, the authors infer that the Bangonghu-Nujiang middle Tethys ocean should be closed at least in the beginning of the Early Cretaceous. |
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| Keywords: | A-type granites zircon U-Pb dating petrogeochemistry oceanic basin slosure Bangonghu-Nujiang suture Tibetan plateau |
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