| 扬子西缘祥云响水花岗岩体的成因:锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素制约 |
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| 引用本文： | 刘桂春,陈光艳,李静,陈棵,孙柏东,马进华,钱鑫,赵天宇.扬子西缘祥云响水花岗岩体的成因:锆石U-Pb年代学、岩石地球化学和Sr-Nd同位素制约[J].地球科学,2020,45(7):2426-2440. |
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| 作者姓名： | 刘桂春 陈光艳 李静 陈棵 孙柏东 马进华 钱鑫 赵天宇 |
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| 作者单位： | 1.昆明理工大学国土资源工程学院, 云南昆明 650031 |
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| 基金项目： | 国家自然科学基金项目“滇西南原特提斯及其与古特提斯演化关系研究”41672222中国地质调查局项目“云南区域地质调查片区总结与服务产品开发”121201102000150012-02中国地质调查局项目“全国陆域及海区地质图件更新与共享”DD20190370 |
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| 摘 要： | 滇西至滇中一带新元古代镁铁质岩类、花岗岩类等岩浆岩有广泛分布，前人利用不同岩石组合指示这些岩浆岩形成于不同的地质构造背景.通过对祥云一带调查研究，新确定了南华纪花岗岩体，花岗岩体中含有大量的超镁铁质岩（橄榄辉长岩）、闪长岩类包体，包体与花岗岩不规则边界呈成分渐变，混合形成为花岗闪长岩、石英闪长岩、英云闪长岩类岩石.对花岗岩和铁镁质包体进行锆石U-Pb LA-ICP-MS同位素测年，获得了相近的206Pb/238U平均年龄:761.9±4.1 Ma、761.7±4.2 Ma、761.3±3.7 Ma和757.5±5.9 Ma.花岗岩主量元素显示具有高碱（alk）、中等Mg#（38~57，平均值为50）、低TiO2、P和亏损Ta、Nb、Sr特点，展现了富集轻稀土元素（LREEs）、亏损重稀土元素（HREEs）和选择性富集大离子亲石元素（LILEs）等特点，并且其εNd（t）为负值（-2.73~-4.90），表明花岗岩浆的物质应为早期古老地壳部分熔融的产物；橄榄辉长岩包体地球化学特征为:低K2O，低稀土总量，LREEs和LILEs略富集或不富集，具明显P负异常，Nb-Ta和Zr-Hf无亏损，具有非常高的Mg#（71~83）等特点，这些特征都指示这些橄榄辉长岩来源于幔源，应为地幔边缘岩浆熔融的产物.花岗闪长岩、闪长岩具有略富集LREE和LILE、亏损HREE，其Mg#（45~71）较高，P亏损、负εNd（t）值等特征，Ta、Nb、Ti、Sr、P略亏损或不亏损，组分介于花岗岩和橄榄辉长岩之间，显示了幔源和古老地壳部分熔融混合特点.这些岩石都展示陆源弧岩浆岩的构造背景，大洋板块向扬子板块俯冲导致幔源物质重熔的结果.
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| 关 键 词： | 花岗岩 铁镁质包体 锆石年代学 地球化学 新元古代 扬子西缘 |
| 收稿时间： | 2020-03-09 |
Petrogenesis of Xiangshui Granite from Xiangyun,in the West Margin of Yangtze Block: Zircon U-Pb Geochronology,Geochemical and Sr-Nd Isotope Constraints |
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| Abstract: | A lot of Neoproterozoic magmatic rocks were reported from west to central Yunnan, while these rocks were regarded that they were formed from different tectonic setting. In this paper, we show some granites keeping well granitic texture from Xiangshui granite batholith in Xiangyun county, including different enclaves such as mafic rocks (olivine gabbro) and diorites. In the field, some rocks of granidiorites, quartz diorites, tonalities were formed with the mixed granitic magma around the mafic rocks. Four similar LA-ICP-MS 206Pb/238U weight mean ages of zircons yield 761.9±4.1 Ma, 761.7±4.2 Ma, 761.3±3.7 Ma and 757.5±5.9 Ma. The granites are characterized by high alkaline, moderate Mg# values (38~57, average 50), low TiO2 and P contents, their trace elements show depleted Ta, Nb, Sr, enrichment LREEs and LILEs, depleted HREEs, and have low εNd(t) values of -2.73 to -4.90. All of the geochemical characters suggest that the granitic laves was the results of partial melt of the ancient crust. The olivine gabbro show low K2O content and total oxide rare earth elements (REEs), slightly to no enrichment LREEs and LILEs, and slightly or no depleted Nb-Ta, Zr-Hf values, but of depleted P, and high Mg# values (71-83, average 77), indicating the origin of these mafic rocks from MORB or the margin MORB melt. The diorites and granidiorites exhibit slightly enrichment LREE and LILE compared to HREE, variable Mg# (45-71, average 56), depleted P element, εNd(t) values of -3.83 to -4.42, slightly to no depleted Ta, Nb, Ti, Sr, P elements, these geochemical values are between those rocks of granites and olivine gabbro, which indicate the result of mix magma of MORB-derived melt and partial melt of ancient crust. In the tectonic diagrams, these rocks are plot into the continental arc field related to subduction of oceanic crust down to the Yangtze block, and the mafic magma of MORB were the result of oceanic crust remelting. |
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