东昆仑五龙沟地区猴头沟二长花岗岩年龄、成因、源区及其构造意义

doi:10.13278/j.cnki.jjuese.201602112

摘要/Abstract

摘要：

对东昆仑造山带五龙沟地区的猴头沟二长花岗岩开展了详细的岩相学、地球化学、锆石U-Pb年龄及Hf同位素的分析测试和研究工作。LA-ICP-MS锆石U-Pb测年表明,猴头沟二长花岗岩的²⁰⁶Pb/²³⁸U加权平均年龄值为(419.0±1.9)Ma,属于晚志留世。岩石地球化学数据表明:猴头沟二长花岗岩属于高钾钙碱性系列的A₂型花岗岩,富SiO₂、K₂O、Y(>33×10^-6)和Yb,贫Al₂O₃和Sr(<100×10^-6),具有强烈的负铕异常;Rb、Th、U、La、Ce、Nd相对富集,Nb、Ta、Ba、Sr、P、Ti亏损。锆石的Hf同位素研究表明,其ε_Hf(t)值为0.2~5.1,对应二阶段模式年龄(T_DM2)为1066~1371 Ma,由此推测花岗岩源区来自中元古代镁铁质下地壳部分熔融。微量元素及其特征比值的构造判别图解表明,猴头沟二长花岗岩形成于早古生代晚志留世东昆仑造山旋回的造山后伸展阶段。据此认为,原特提斯洋在东昆仑地区的最晚闭合时限应该不晚于晚志留世末期(~419 Ma),而不是前人认为的早泥盆世。

关键词: 猴头沟二长花岗岩, 岩石地球化学, 锆石U-Pb定年, Hf同位素, 东昆仑

Abstract:

This paper presents a detailed research work on LA-ICP-MS zircon U-Pb geochronology, geochemistry, and zircon Hf isotope of the Houtougou monzogranite in Wulonggou area of the eastern Kunlun orogen. The LA-ICP-MS zircon dating of the Houtougou monzogranite yields an average ²⁰⁶Pb/²³⁸U age of (419.0±1.9) Ma, belonging to Late Silurian. Its geochemical features show that the Houtougou monzogranite belongs to a high-K calc-alkaline series of A₂-type granite, and is characterized by high SiO₂, high K₂O, high Y (>33×10^-6) and Yb, low Al₂O₃ and Sr (<100×10^-6), with a significant negative Eu anomaly, enriched in Rb, Th, U, La, Ce, and Nd, depleted of Nb, Ta, Ba, Sr, P, and Ti. The zircon Hf Isotopic data demonstrate that their ε_Hf(t) values range from 0.2 to 5.1 with the model ages (T_DM2) of 1066 to 1371 Ma. It implies that their primary magma was likely derived from partial melting of lower Mesoproterozoic mafic crust. The trace elements and their characteristic ratios show that the Houtougou monzogranite emplaced in the post-orogenic stage of the eastern Kunlun orogen in Late Silurian. In view of the above facts, the closure of Proto-Tethys occurred in Late Silurian (~419 Ma) rather than Early Devonian in the eastern Kunlun orogen.

Key words: Houtougou monzogranite, lithological geochemistry, zircon U-Pb geochronology, zircon Hf isotopic systematic, eastern Kunlun orogen

中图分类号:

P588.121

严威, 邱殿明, 丁清峰, 刘飞. 东昆仑五龙沟地区猴头沟二长花岗岩年龄、成因、源区及其构造意义[J]. 吉林大学学报(地球科学版), 2016, 46(2): 443-460.

Yan Wei, Qiu Dianming, Ding Qingfeng, Liu fei. Geochronology, Petrogenesis, Source and Its Structural Significance of Houtougou Monzogranite of Wulonggou Area in Eastern Kunlun Orogen[J]. Journal of Jilin University(Earth Science Edition), 2016, 46(2): 443-460.

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