Mineralogical Study On The Clinopyroxene Megacrysts In The Cenozoic Basalt From Maguan Yunnan Province

There are abundant Cenozoic volcanic rocks in Maguan area, Southeastern Yunnan province due to Indo-Asian collision and uplift of whole Tiet Plateau quick since late-Cenozoic Era. There are rich typhonic rocks stone inclusion and the clinopyroxene megacrysts and the garnet megacrysts in this basalt of Maguan. The predecessor has conducted massive research of the xenolith of mantle, but the megacrysts research is a blank. This paper research mineralogy and geochemistry of clinopyroxene megacrysts in Maguan by the traditional petrography method of the electron probe, the laser ICP-MS analysis;and obtainde equilibrium temperatures and pressures of the clinopyroxene megacrysts using the mineralogical thermobarometer; and carries on the preliminary discussion to the megacryst 's origin.The characteristics of major element falls into the rang of the east China pyroxene megacrysts'characteristics;and has slightly high Mg# and obvious somewhat low Cr#,which explained that the mantle crag was fused the extraction the degree to be very low .Thetre are very good relevance am among major elements which explains clinopyroxene megacrysts from the identical rock magma.Pyroxene megacrysts belong to Al-augite according to computation of the crystal chemical formula computation and pyroxene nomenclature of CaMgSiO6 - CaFeSiO6 - Mg2SiO6 - Fe2SiO6. The rare earth element was tested by La-ICP-MS, after caculating and analysis, the total quantity of the three sample rare earth which were measured by the home court is: 52.33×10-6, 56.16×10-6, 28.11×10-6, which is concentrates the light rare earth weakly, Eu is usual, but Pr is unusual, the rare earth distribution curve fitting degree is very good, which is further showed the products were the vary degree evolves by the same rock magma. The results showed that equilibrium temperatures and pressures of the clinopyroxene megacrysts were from 1152 to 1356℃and 19×108 ~27×108Pa based on using several method. In other words, clinopyroxene megacrysts was formed in 6363～86km.The Kcpxd(Fe-Mg)values(0.2 to 0.4) indicate that they were crystallized from hosted basaltic magma under high pressure.The compositional and original comparability between the clinopyroxene megacrysts host in late-Cenozoic basalts from Maguan and Easten China respectively suggest that Maguan area were under the uniform dynamic background and the rock magma depth portion dynamics mechanism.