威宁宣威组底部硅质页岩Rb-Sr古混合线年龄及其地质意义  

THE AGE OF SILICEOUS SHALE IN THE LOWER PART OF THE XUANWEI FORMATION IN WEINING AND ITS GEOLOGICAL IMPLICATION

作　　者：许连忠[1] 张正伟[1] 张乾[1] 朱笑青[1] 祝朝辉[1] 黄艳[1] 黄海明[1] 

机构地区：[1]中国科学院地球化学研究所矿床地球化学国家重点实验室

出　　处：《矿物学报》2006年第4期387-394,共8页Acta Mineralogica Sinica

基　　金：中科院知识创新工程重要方向项目(KZCX2-SW-125)

摘　　要：在滇黔相邻地区,二叠纪宣威组下部发育一层硅质页岩和碳质页岩。页岩层位稳定、分布广泛,与下伏峨眉山玄武岩组上部凝灰岩层呈假整合接触关系。用迭代法恢复硅质页岩的Rb-Sr同位素古混合线,得到硅质页岩的年龄为(255±12)Ma。这个年龄不仅支持地层古地磁研究结果,而且符合地层年代学研究结果,表明Rb-Sr同位素古混合线年代学方法在中生代地层能够适用。这个年龄与普遍认为的峨眉山玄武岩主喷发期258Ma从时代关系上相符,而且有效地约束了峨眉山玄武岩喷发的上限。A layer of siliceous shale and carbonaceous shale deposits occur steadily at the bottom of the uppermost Permian Xuanwei Formation, which is spread widely in the adjacent areas of Guizhou and Yunnan provinces. The deposits rest disconformitily on the Emeishan Basalt Formation. This paper dated the binary isotope paleomixing line of the shale by iterative reconstruction and regression of corresponding two-component mixing line from conventional Rb-Sr dating. From the research, we obtained the shale age of 255±12 Ma （MSWD= 0.17, probability = 0.96）. This age not only supports the study of paleomagnetism of strata and strata chronology, but also suggests Emeishan basalts host eruption time is nearly 258 Ma. This study indicates Rb-Sr isotope chronology is applicable in Mesozoic strata and the age of 255 Ma effectively restraints the upper limit time of Emeishan basalt eruption.

关 键 词：硅质页岩 古混合线 RB-SR定年 峨眉山玄武岩 喷发上限 

分 类 号：P597[天文地球—地球化学]