滇西北贡山地块始新世花岗岩的成因及其构造意义

发布时间：2018-09-07 19:08

【摘要】：滇西三江地区发育古近纪花岗岩,记录了印度-欧亚大陆碰撞的岩浆活动信息。对贡山地块福贡花岗岩开展岩石地球化学及锆石U-Pb-Hf系统研究,结果表明,该花岗岩为钙碱性、过铝质特征的I-S型花岗岩。锆石U-Pb同位素分析表明,福贡马吉花岗岩侵位于55 Ma,并含有252~77 Ma的继承锆石。锆石Hf同位素分析表明,该区岩浆锆石具有与青藏高原及东其南缘同时代长英质侵入体相似的Hf同位素组成,暗示其相似的岩浆起源。微量元素和同位素组成模拟计算结果表明,马吉花岗岩的原生岩浆是由53%的新生地壳组分和47%古老地壳基底物质混合而成的原岩经5%~15%(F=0.05~0.15)的部分熔融而成。贡山地块福贡马吉花岗岩与冈底斯地块和腾冲地块早始新世岩浆岩(约55Ma)具相似的年龄及地球化学特征,暗示它们之间可能存在类似的成因机制,均为新特提斯洋俯冲板片断离引起的壳内减压熔融的产物。
[Abstract]:Paleogene granites were developed in Sanjiang area, western Yunnan, and magmatic activity information of India-Eurasia collision was recorded. Rock geochemistry and zircon U-Pb-Hf system of Fugong granite in Gongshan block are studied. The results show that the granite is an I-S type granite characterized by calc-alkaline and peraluminous features. The U-Pb isotopic analysis of zircon shows that the Fugomagi granite is located at 55 Ma, and contains 2522 Ma inherited zircon. The Hf isotopic analysis of zircon shows that the magmatic zircon in this area has a Hf isotopic composition similar to that of the felsic intrusions of the same age in the Qinghai-Tibet Plateau and the southern margin of the eastern part of the Tibetan Plateau, implying a similar magmatic origin. The simulation results of trace elements and isotopic compositions show that the primary magma of the Magi granite is formed by the partial melting of 53% of the new crustal components and 47% of the old crustal basement material through the partial melting of 515% (F0. 05 ~ 0. 15%) of the primary magma. The Fugongmaji granite in the Gongshan block has similar age and geochemical characteristics to the early Eocene magmatic rocks (about 55Ma) of the Gangdis and Tengchong massif, suggesting that there may be a similar genetic mechanism between them. All of them are the products of vacuum melting caused by the partial separation of the new Tethys subduction plate.
【作者单位】：中国地质大学(北京)地球科学与资源学院;山东省地矿工程勘察院;江西省地质矿产开发研究中心;核工业金华工程勘察院湖州分院;
【基金】：国家自然科学基金项目(41473015,41502212,41530207)
【分类号】：P588.121

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