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

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εHf(t)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。

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 lowεHf(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.