吉林南部荒沟山地区侏罗纪花岗岩地球化学特征及构造意义

Geochemical characteristics and tectonic significance of Jurassic granites in Huanggoushan area,south of Jilin,China

通过对岩体进行野外地质调查、硅酸盐全分析、稀土微量分析以及LA-ICP-MS锆石U-Pb法测定年龄,探讨吉林南部荒沟山地区侏罗纪花岗岩形成的动力学环境。结果表明,荒沟山地区的老秃顶子岩体和草山岩体的LA-ICP-MS锆石U-Pb年龄为178～181 Ma;主要岩石类型为似斑状黑云母花岗岩;岩石具有较高的SiO2含量(质量分数为72.04%～73.68%),为准铝质到过铝质的高钾钙碱性Ⅰ型花岗岩;稀土元素总量(质量分数为94.24×10-6～170.14×10-6),具有右倾的稀土元素配分模式,中等的负铕异常(δEu=0.51～0.69);在原始地幔标准化蛛网图中,富集K、Rb、Th等不相容元素,亏损Ba、Nb、Ta、P、Ti等,具有活动大陆边缘岩浆弧的地球化学特征。其形成与古太平洋板块向华北板块的俯冲有关。

By the field geological survey of the rocks, silicate full analysis, trace elements analysis and LA-ICP-MS zircon U-Pb dating, the authors explore the dynamics environment of the granite from the Huanggoushan area in the south of Jilin Province of China. The results show that the Laotudingzi and Caoshan plutons which LA-ICP-MS zircon U-Pb age is 178-181 Ma, consist mainly of biotite granite in the Huanggoushan area. The intrusions have high silica content （the mass fraction of SiO2 is 72.04%-73.68%） and belong to metaluminous to peraluminous high-K calc-alkaline I-type granite. The REE （the mass fraction of -REE is 94.24×10^-6～170.14×10^-6） have the right-deviation patterns and moderate negative Eu anomaly （δEu=0.51-0.69）. On the primitive mantle-normalized spider diagrams, the granites show positive K, Rb and Th anomalies and negative Ba, P, Ti, Nb, Ta anomalies, having the geochemical characteristics of an active continental margin magmatie arc, and their formation is related to the subduction of the ancient Pacific plate to North China plate.