峨眉山大火成岩省东区普安玄武岩系年代学、地球化学及成因研究

广泛分布于中国西南川、滇、黔三省的峨眉山玄武岩是我国最早被国际认可的大火成岩省,受到了国内外学者的广泛关注.前人对大火成岩省西区玄武岩已达成多项共识,而对东区玄武岩的岩石组合、火山活动时限、岩石成因等方面还存在诸多争议.本文以峨眉山大火成岩省东区贵州普安玄武岩系为研究对象,通过解析典型剖面,明确该区玄武岩系岩石类型从底...

Geochronology, geochemistry and petrogenesis of the Pu'an basalt succession from eastern Emeishan large igneous province

Emeishan basalts, widely distributed in Sichuan, Yunnan and Guizhou in southwestern China, are the earliest internationally recognized large igneous provinces in China and have been favored by a large number of experts both in China and abroad. Many consensuses have been reached on the basalt in the western part of the Emeishan large igneous province (ELIP), but there are still several controversies in such aspects as the rock associations, the time limit of volcanic activities and the genesis of rocks. With the basalt of Pu''an in western Guizhou, eastern part of ELIP as the study object and through the analysis of typical basalt profiles, the authors detected that the rock types in this area are eruptive facies of volcanic breccia in the first cycle, flooding facies of basalt in the second cycle and volcanic sedimentary facies of tuff in the third cycle from bottom to top. Zircon LA-ICP-MS U-Pb dating from the tuff which is located at the top of the basalt defined the upper time limit of volcanic activity in the east of the ELIP to 250 Ma. The major and trace elements indicate that the basalts in this area are mainly high-Ti and alkaline basalts. The characteristics of Rb-Sr depletion and Ba-Hf enrichment are basically consistent with the geochemical characteristics of basalts in Guizhou, high Ti basalts in the west of ELIP, and OIB. Trace elements show that the origin of the basalt is metasomatic garnet mantle peridotite, and the melt generated by partial melting when rising from the deep mantle plume to the stable area of garnet peridotite was mixed with the continental lithospheric mantle enriched with metasomatic fluids. Crystallization differentiation was significant while the crustal mixing degree was weak during the ascent and migration of magma. The results show that the basalt in the eastern ELIP was formed in the environment of greater depth, low partial melting and high pressure at the edge of the mantle plume.