塔里木盆地二叠纪玄武岩的地球化学特征及其与峨眉山大火成岩省的对比

Geochemical features of Permian basalts in Tarim Basin and compared with Emeishan LIP

中国西部地区发育了塔里木大火成岩省和峨眉山大火成岩省,分别形成于280Ma左右和258～260Ma。对比两个大火成岩省的玄武岩的地球化学特征,发现塔里木玄武岩的岩石地球化学特征与峨眉山玄武岩相似,Fe_2O_3=15.29%～17.97%,大于10%,比MORB富铁,指示其深源以及地幔柱源特征,为典型的溢流玄武岩。稀土元素比值显示其落在由石榴石二辉橄榄岩组成的原始地幔熔融线上,表明该玄武岩是在厚的岩石圈下由异常热的地幔经低部分熔融形成的。微量元素特征比值分析,揭示了塔里木玄武质岩浆在上升过程中受到了一定程度的地壳混染。塔里木大火成岩省和峨眉山大火成岩省一样,可能起源同一个来自于核幔边界的超级地幔柱,它们很可能是塔里木板块和扬子板块在二叠纪北向漂移过程中先后穿越同一个超级地幔柱的结果。

In western part of China there are two large igneous provinces(LlPs) : Tatim LIP and Emeishan LIP. The former one formed ca. 280Ma, while the latter 258 similar to 260Ma. Comparing the geochemical features of the basalts from two Lips, these Permian basalts from Tarim have got the same geochemical characteristics as Emeishan basalts. Tarim basalis are enriched in Fe, Fe(2)O(3) = 29% similar to 17.97%, more than that in MORB, which tells that they are typical flood basalts coming from deep source and related to mantle plume. Ratios of rare earth elements can be used to discriminate originations of igneous rocks. From the diagram of La/Sm-Sm/Yb, we can see the samples are all above the melting line of primitive mantle composed of garnet lherzolite. That means the basalts came from low-degree partial melting of the extreme hot mantle beneath the thick lithosphere. Trace element ratios imply that the basaltic magma underwent contamination while penetrating through the continental crust. Tarim LIP resembles Emeishan LIP, i.e. they probably came from the same super mantle plume originated at the core-mantle boundary. They were coming into being while the Tarim plate and Yangtz plate were passing above the same super plume early or late because of their northward drifting in Permian.