| 摘要: |
| 选择3个典型岩体，即位于西南天山东段的拜城县英买来岩体和位于西段阔克萨岭区的川乌鲁岩体、巴雷公岩体（为了对比，也选择了位于塔里木盆地西北缘的麻扎山岩体），进行了岩石学和地球化学研究。结果表明，这些岩体具有不同的特点。英买来岩体为黑云母花岗岩和二云母花岗岩，具有高的SiO2含量，弱过铝，高的Sr同位素初始值（约0.710）和负的εNd(t)值（-4～-6），属于S—A型之间的过渡类型。麻扎山岩体由正长岩组成，属于碱性岩，微量元素标准化图解和其他岩体明显不同的是没有明显的Nb和Ta的负异常。川乌鲁岩体是一个由3个不同期次岩石组成的杂岩体，主体为正长岩-二长岩，地球化学特征显示是由基性岩浆和酸性岩浆不同程度混合形成的。位于同一构造区的巴雷公岩体则与川乌鲁岩体中的花岗斑岩的地球化学特征相似。综合岩石学和地球化学特征推测，南天山东段的英买来岩体是地壳熔融的结果，没有任何地幔物质加入的地球化学信息，西段的阔克萨岭地区酸性岩浆的形成则可能是来自于幔源底侵的基性岩浆导致薄的地壳发生熔融的结果。麻扎山岩体则完全是不同构造背景的产物，有可能与发生在塔里木盆地的二叠纪大规模的岩浆活动有关。因此，二叠纪岩浆活动的性质主要受地壳成分和结构的控制。 |
| 关键词: 中酸性侵入岩 地壳厚度 岩石圈地幔 软流圈地幔 底侵作用 西南天山 |
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| Geology and geochemistry of the Permian intermediate-acid intrusions in the southwestern Tianshan, Xinjiang, China: implications for petrogenesis and tectonics. |
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ZHANG Zhao-chong, DONG Shu-yun, Huang He, MA Le-tian,ZHANG Dong-yang, ZHANG Shu, XUE Chun-ji
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State Key Laboratory of Geological Processes and Mineral Resources/China University of Geosciences, Beijing 100083, China
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| Abstract: |
| Four typical intrusions, i.e., Yingmailai intrusion in the east part of the south Tianshan, Chuanwulu and Baleigong intrusions in the Kuokousaling regions and Mazashan intrusion in the northwest Tarim Basin, are chosen for petrological and geochemical investigations. These intrusions which come from three different regions have distinct geochemical characteristics. The Yingmailai intrusion consists of biotite granite and two-mica granite, which are characterized by high SiO2 contents, weak aluminium-oversaturated feature, high initial Sr isotopic ratios (around 0.710） and negative εNd(t) values（-4 to -6）. So it can be classified into S-A transitional type. The Mazashan intrusion is alkali, and composed of syenite, which is characterized by absence of significantly negative Nb and Ta anomalies on primitive mantle normalized trace element patterns. The Chuanwulu intrusion consists predominantly of syenite and monzonite. The systematic geochemical investigations suggest that the syenite and monzonite are formed by mixing of mafic magma with felsic magma in different ratios. Comparably, the Baleigong intrusion has similar geochemical features with granite porphyrite. In combination with petrological and geochemical characteristics, we suggest that the Yingmailai intrusion in the east part of the south Tianshan was produced by partial melting of "cool" thickened crust induced by radiogenic heating, whereas the felsic rocks were formed by partial melting of thin crust in response for underplating of mantle-derived mafic magma. In contrast, the Mazashan intrusion was formed in a different tectonic setting, which can be attributed to Permian large magmatic event in the Tarim basin. Consequently, the nature of the Permian magma is controlled by the compositions and structure of crust. |
| Key words: intermediate-acid intrusion crust thickness lithosphere mantle asthenosphere mantle underplating activity southwest Tianshan |