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    云南安宁地区石虎山花岗岩年代学、地球化学特征和锆石Hf同位素组成及其成因

    Geochronology, geochemistry, zircon Hf isotopic composition and genesis of Shihushan granite in Anning, Yunnan Province

    • 摘要: 石虎山花岗岩岩体位于安宁市德滋村附近,本文对该岩体开展了LA-ICP-MS锆石U-Pb定年、岩石地球化学、锆石Hf同位素组成研究。结果获得(616±20)Ma的岩浆结晶年龄和(839±17)Ma、(766±15)Ma、(705.5±9.4)Ma的继承性年龄,说明岩体形成于新元古代埃迪卡拉纪;其中(839±17)Ma、(766±15)Ma、(705.5±9.4)Ma的继承性年龄组合可能是Rodinia超大陆裂解构造过程的记录,839 Ma、616 Ma可能是Rodinia超大陆在扬子板块西缘开始裂解与最终裂解时限。花岗岩主量、微量元素特征显示,其产生于伸展环境的高硅、过铝、高钾的A型花岗岩;锆石εHft)值均小于0,在t-t(Ma)和t-(176Hf/177Hf)图上,所有样品点均落在上地壳演化线之上,二阶段模式年龄变化范围为1.77~2.31 Ga,结合Nb/Y—Rb/Y图解,表明成岩物质主要来源于古元古代古老下地壳页岩60%部分熔融。

       

      Abstract: The LA-ICP-MS zircon U-Pb age, rock geochemistry and zircon Hf isotopic composition of the Shihushan granite located in Dezi Village of Anning area were investigated in this study. The zircon U-Pb dating yielded a magmatic crystallization age of (616±20) Ma and inherited ages of (839±17) Ma, (766±15) Ma and (705.5±9.4) Ma, indicating pluton emplacement in Neoproterozoic Ediacaran Stage. The authors hold that the magmatic crystallization age of (616±20) Ma indicates the pluton emplacement in Neoproterozoic Ediacaran Stage, and the assemblage of inherited ages of (839±17) Ma, (766±15) Ma and (705.5±9.4) Ma represents the splitting of the Rodinia supercontinent. The age of (839±17) Ma may represent the initiation of the breakup of the Rodinia supercontinent, while the age of (616±20) Ma may represent the final stage of the breakup event. The major and trace elements of alkali feldspar granite show the characteristics of A-type granite with high SiO2-K2O-Al2O3 content, indicating an extensional environment. Zircons from samples have low εHf(t) value (< 0). All samples are plotted on the upper crustal evolution area on t-t (Ma) and t-(176Hf/177Hf) diagrams. The two-stage Hf model ages range from 1.77 Ga to 2.31 Ga. According to the Nb/Y-Rb/Y diagram, the petrogenic material mainly originated from the 60% melting of the shale of the Paleoproterozoic lower crust.

       

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