四川冕宁基性岩墙的年代学、地球化学特征及其地质意义  

Geochronology,Geochemistry and Geological Significances of the Permian Basic Dykes in Mianning,Sichuan Province

作　　者：李宏博[1,2] 张招崇[1] 吕林素[2] 李永生[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083 [2]中国地质博物馆,北京100034

出　　处：《地质论评》2012年第5期952-964,共13页Geological Review

基　　金：科技部973项目(编号2009CB421002);国家自然科学基金资助项目(编号40925006);教育部博上点基金资助项目(编号20090022110006);111计划(编号B07011)地质过程与矿产资源国家重点实验室开放课题基金项目(编号GPMR2011)的成果

摘　　要：本文对四川冕宁地区的基性岩墙进行了年代学、岩石学和地球化学研究。主量元素特正和微量元素标准化图解显示,基性岩墙属于拉斑玄武岩系列,具有洋岛玄武岩(OIB)的特征,与峨眉山玄武岩为同源产物,存在密切的成因关系。微量元素示踪、Th/Hf-Ta/Hf判别图表明,冕宁基性岩墙具有地幔柱成因的特征,并遭受了轻微混染。基性岩墙锆石LA-ICP-MS测年结果表明,岩墙形成年龄为256.7±4.3Ma,表明岩墙是峨眉山大火成岩省大规模岩浆作用晚期的产物。年龄测定结果还暗示了岩墙在约244Ma遭遇了一次变质事件,可能是岩浆热——机械侵蚀作用,以及印支运动诱发岩浆作用再次活跃的结果。Geochronology, petrology and geochemistry were performed systematically on basic dykes in Mianning, Sichuan province. On the basis of major and trace elements patterns, basic dykes belong to tholeiitic basalt serie in lithology and have OIB （Ocean island basahs） features, which were homologous with Emeishan basalts. Trace elements tracing and Th/Hf--Ta/Hf identification diagram show that basic dykes were derived from mantle plume with little contamination. The LA-ICP-MS U-Pb zircon data of basic dyke yields a concordant age, 256.7±4.3Ma, which may represents the rock mass crystallization time. It shows that the Mianning basic dykes were formed in the late period of Emeishan mantle plume magmatism. In addition, the dating implies that dykes experienced geological events occurred about 244Ma, which was caused by thermal erosion of magma and triggered by the Indosinian movement.

关 键 词：峨眉山大火成岩省 地幔柱 基性岩墙 锆石LA—ICP—MS U—Pb定年 冕宁 

分 类 号：P597.3[天文地球—地球化学]