Petrology And Geochemistry Characteristics Of Emeishan Basalts Of Yanyuan, Sichuan

Emei large igneous province locates in the Yangtze cratonic margin, it is the onlylarge igneous province recognized by international academia,it is an important oreconcentration area in the southwest of our country,its causes relate to mantle plumeactivity. Emeishan basalt as the deep source material, its main content, rare earth,trace and PGE features have deep large amounts of information. Yanyuan county islocated in the junction of Sichuan and Yunnan provinces, the area has good basaltexposure and complete basalt geologic profile, it provides a good conditions for thestudy of emeishan basalt in Yanyuan region. This article bases on the basis ofpetrological and geochemical characteristics of Yanyuan Emeishan basalt in theresearch area, and summarizes its characteristics compared with other region whichhas the emeishan basalt. Through the petrological and geochemical study，we canexplore its primary magma, assimilation contamination, fractional crystallization, themagma source region,etc.The author finds out its lithological characteristics through field geologicalinvestigation: Permian emeishan basalt of Yanyuan area in the volcanic formation isgiven priority to small amounts of sedimentary rocks. Rocks in black and sage green,according to its causes and characteristics of structure component,Yanyuan emeishanbasalt can be divided into four types of porphyritic basalt, porosity, almond basalt,trachytic basalt, crystalline basalt rock., It can be subdivided picrite series (whichcontain Meimechite and Komatiite) and trachyte series based on the analysis ofgeochemical data.Experiments on the sample data were analyzed, and the mainelements in the aspects of rock series cast part figure evenly into potassium high kcalc alkaline series-calcium alkali series range, most fall into the low potassiumseries. SiO2and content of MgO style change is bigger, may be due to the rock silicide, carbonatization,or due to weathering. The content of MgO style change isbigger, may be because of the existence of olive figured rocks containing olive figuredMgO style content greater than15%. TiO2content1.92on average, significantly isless than other regions; Enrichment of rare-earth elements, re content, fractionationbetween light and heavy rare earth elements, light rare earth concentration degree ishigh, the Eu is slightly negative anomaly;Trace elements, large ion lithophile elementscontent of volatile, weak loss of high field strength elements Nb, Ta, P, Sr and K areobvious abnormalities, large variation between high concentration and lowconcentration. Sr exception, may be in plagioclase was caused by fluid metasomaticalteration. PGE, Yanyuan emeishan basalt has a very high content of PGE. Ru and Pt,Pd, relative to the Ir and Rh.Ru overall performance for the negative anomaly, on thewhole Pd/Ir value is greater than the primitive mantle, chondrite values (1.22)(1.01)is the value, indicating the emeishan basalt source area with less experienced meltingof upper mantle.Analysis results show that, in addition to higher Mg#,picrite is close totheoriginal magma,the rest of the basalt is formed in the evolution of magma frommoderation.Basalt prolific in source area in the study area for the garnet lherzolitemantle,but at the same time,some sample blending in the earth’s crust material,magmatism, olivine, pyroxene, plagioclase and produce more apparent separation andcrystallization.