Rock Geochemistry And Diagenetic Evolution Of Early Permian Woniusi Formation Basalt In Baoshan City, Yunnan Province

Yunnan Baoshan Early Permian Woniusi formation basalts located in Baoshan zhenkang massif which is on the west side of Changning--Menglian belt in Sanjiang area of Eastern Tethys, the land is a continental block with relatively stable Paleozoic--Early Mesozoic sedimentary sequence. According to the complex of it’s structural feature, there is not enough previous research on this area, and still exist a lot of controversy.Wo Niusi Group basalt combination including alkaline basalt and sub alkaline basalt, the majority type is alkaline basalt, small amounts of the outcropping rock are basaltic trachyte rocks and andesite. In microscope olivine phenocrysts of some of the samples are visible and have some crack on it, but most of them are iddingsite. Through the diagram of probe data pyroxene phenocrysts display in basalts is augite, through the data and diagram analysis, showing the basalt is of sodic alkaline basalt series, and the charicteristics are LREE is relativly rich, while HREE is deficit, REE differentiation is obvious. EU has no obvious abnormalities(δEu=0.91-1.04), all the samples have negative Ce anomaly, indicating the weak plagioclase fractionation crystallization and rapid migration in the process of the evolution of magma, all samples strongly riched in Pb but strongly depleted in K, P, Ti. abundance of unstable element such as Rb,Sr, Ba fluctuates significantly, and La/Ta(10.8~16.7) shows that the basaltic magma did not experience the mixing of the lithosphere mantle. Studies suggest that the basalts are the product of partial melting about 10%--30% in enriched mantle garnet lherzolite, in the process of rock forming magma mainly experienced fractional crystallization of clinopyroxene, feldspar crystallization is weak, crustal contamination is not significantly influeced the magma. According to the probe data and pyroxene temperature pressure formula the calculation of the ordinary pyroxene phenocrysts temperature is 1067-1310 ℃ and the pressure is 0.3-1.4GBa, rock melting depth is about 80 km deep, so the source region is the garnet peridotite stability area, the magma derived from the partial melting of the enriched mantle.Comprehensive study shows that period of Early Permian Bao Shan--Zhen Kang massif split out from Gondwana, at the same time, influenced by effect the closure of the Chang Ning--Meng Lian ocean, Baoshan--Zhen Kang massif mainly controled by stretching and discrete action. At the same time period, Woniusi formation basalts formed in pull continental rift environment, magma comes from partial melting of the enriched mantle and it not obviously interacted by other substances and not experienced crystallization differentiation through rapid solidification process after it quickly migrate to the surface along the fracture passage, Woniusi formation basalts are overflow facies basalts, eruption mode is the central type eruption;...