The Accumulation Sequence And Lithologic And Lithofacies Characteristics Of The Basalt In Mount Emeishan,Southwest Sichuan

The basalt of mount emeishan in the southwest of Sichuan province is located in the northeast margin of the Yangtze platform.Two eruption cycles were determined by systematic study.The lower cycle is mainly composed of coarse basalt and a small amount of basalt coarse andesite,which is the main part of the basalt of emeishan.The upper cycle is composed of quartz coarser,rhyolite pyroclastic and alkaline basalt,and the upper and lower cycles are in regional unconformity contact.The rocks of basalt and basaltic basalt in the lower cycle are characterized by high ferric titanium,low magnesium and alkali rich,which belong to the alkaline basalt of low magnesium and high iron titanium.The profile is characterized by reverse stacking.Magma originated from the upper mantle and underwent a complex evolutionary process.The supercycle is a typical "bimodal" volcanic assemblage.The acid terminal element mainly comes from the lower crust.The types of pyroclastic rocks in the area are complex and widely distributed,among which the determination of fused tuff,fused breccia,fused deposit and bean grain tuff is of great significance to the volcanic recovery process.Volcanic facies include eruptive facies(pumice flow accumulation,falling accumulation,falling accumulation,sputtering accumulation),overflow facies,eruptive sedimentary facies,eluvial lithofacies,intrusive lithofacies,and subsurface volcanic lithofacies.The newly determined fluvial accumulation,fluvial accumulation and fluvial deposit are of great significance to the determination of reservoir.Volcanic rock accumulation environment,the bottom and middle and upper part of the lower cycle are underwater accumulation,marked by the development of eluvial rock,quenching breccia,phosphate rock and argillaceous siltstone interlayer.The central and the top are continental deposits marked by rock flow units,multi-row small columnar joints and fused breccia.The lower cycle of volcanic activity was fissure-center type,and in its late stage,both of them were point-type Hawaiian and stonembert eruptions.The upper cycle is the central type of eruption,and the eruption area is obviously moving into the basin.The volcanic mechanism is a broken volcano characterized by a strong eruption of intermediate-acid magma.The lower and middleupper parts of the lower cycle are relatively good reservoirs.These sites are mainly underwater accumulation,development of eluvial rocks,quenched breccia,generally with sodium feldspathic,stomata and gas condensate tube development.The intermediate-acid pyroclastic rocks of the upper cycle are good reservoirs.