| 柴北缘都兰高压麻粒岩的锆石U-Pb定年及其地质意义 |
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| 引用本文： | 于胜尧,张建新,李金平,孟繁聪.柴北缘都兰高压麻粒岩的锆石U-Pb定年及其地质意义[J].岩石矿物学杂志,2010,29(2):139-150. |
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| 作者姓名： | 于胜尧 张建新 李金平 孟繁聪 |
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| 作者单位： | 中国地质科学院,地质研究所,北京,100037 |
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| 基金项目： | 国家自然科学基金资助项目，中国地质科学院地质研究所所长基金，中国地质科学院院长基金，中国地质调查局地质调查资助项目 |
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| 摘 要： | 在柴北缘高压-超高压变质带的东端都兰地区,高压麻粒岩以透镜体的形式存在于石榴白云母片岩、花岗质片麻岩以及斜长角闪岩中。高压麻粒岩的主体为基性麻粒岩,并含少量中酸性麻粒岩。基性麻粒岩主要由石榴子石、单斜辉石、斜长石和石英等组成,而中酸性麻粒岩峰期矿物组合为:石榴子石+斜长石+钾长石+蓝晶石+石英±单斜辉石。根据显微构造和反应结构特征,主要识别出3期变质作用:①峰期高压麻粒岩相阶段(M1);②退变质高角闪岩相阶段(M2);③绿片岩相/低角闪岩相阶段(M3)。选取典型的中酸性麻粒岩样品进行了锆石LA-ICP-MSU-Pb原位定年分析,获得加权平均年龄为446.9±6.5Ma,且CL图像显示锆石内部发育石榴子石、单斜辉石、斜长石等矿物包体,反映锆石可能形成在峰期高压麻粒岩相变质条件下。岩石学和年代学结果显示都兰高压麻粒岩和邻近的榴辉岩同时形成于同一俯冲带的不同热构造环境,高压麻粒岩并非榴辉岩热松弛作用形成的,两者具有各自独立的变质演化历史。
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| 关 键 词： | 都兰 高压麻粒岩 锆石U-Pb年龄 |
Zircon U-Pb geochronology of high-pressure granulite and its tectonic implications in the Dulan area, North Qaidam Mountains, western China |
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| YU Sheng_yao,ZHANG Jian_xin,LI Jin_ping and MENG Fan_cong.Zircon U-Pb geochronology of high-pressure granulite and its tectonic implications in the Dulan area, North Qaidam Mountains, western China[J].Acta Petrologica Et Mineralogica,2010,29(2):139-150. |
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| Authors: | YU Sheng_yao ZHANG Jian_xin LI Jin_ping and MENG Fan_cong |
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| Institution: | Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China |
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| Abstract: | High-pressure granulite occurs as lenses in muscovite schist, granitic gneiss and amphibolite of Dulan area at the eastern end of North Qaidam HP-UHP metamorphism terrane, Northwest China. The high-pressure granulite could mainly be divided into two types: mafic granulite and acid-intermediate granulite. The dominant mafic granulite is composed of garnet, clinopyroxene, plagioclase and quartz, whereas the peak assemblage of intermediate-acid granulite is composed of garnet, plagioclase, K-feldspar, clinopyroxene, kyanite and quartz. Based on microstructure and reaction textures, the authors have recognized three main metamorphic stages from the high-pressure granulite: ① the estimated p-t conditions for the metamprphic peak stage of high-pressure granulite facies (M_1) were 1.4～1.85 GPa and 800～925℃;② retrogression began at the high amphibolite facies stage (M_2) with p-t conditions of 0.8～1.05 GPa and 580～695℃;③ subsequent retrogression occurred at the green-schist/high-amphibolite facies stage (M_3). Combined with cathodoluminescence patterns and mineral inclusions(garnet, clinopyroxene and plagioclase inclusions in zircon), U-Pb dating of zircons revealed that the peak metamorphism age of the high-pressure granulite-facies is 466.9±6.5 Ma. Petrological and chronological studies suggest that the granulite and adjacent eclogite were formed in different thermal environments of the same subduction zone, i.e., the ecolgite was formed in the subduction zone while the high-pressure granulite was formed at the root of the thickened crust above the seduction zone. The high-pressure granulite experienced its unique metamorphic history, and was not associated with the action of thermal relaxation after the eclogite-facies metamorphism recorded in adjacent eclogites. |
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| Keywords: | Dulan high-pressure granulite U-Pb age of zircons |
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