Research On Crystal Populations And Deep Magmatism Of Mafic Intrutions In Miyi QingPi Region

There are many layered mafic-ultramafic intrusions in the Panzhihua,Taihe,Hongge,and Baima areas,which formed vanadium-titanium magnetite giant ore bodies.But the hydrous mafic magma in Miyi area has no iron ore.This paper has gave a detailed study through following methods including petrography,EPMA,MC-ICPMS,mineral melt equilibrium thermometer,mineral hygrometer,oxygen fugacity barometer,Magma Sat MELTS geochemical thermodynamic software simulation,etc.This study has compared with the Panzhihua pluton and the Baima pluton,the main conclusions are as follows:(1)The main minerals of olivine,clinopyroxene,and plagioclase in the Qingpi intrusive body belong to complex crystal populations,which are not from simple magma chamber.(2)The olivine melt equilibrium thermometer calculated that the crystallization temperature of olivine in Qingpi intrusions ranged from 1350?to 1287?,The magnesium value of clinopyroxene in the fine-grained biotite gabbro in Qingpi intrusion is lower than the Panzhihua and Baima intrusions.The calculation results of the clinopyroxene-melt equilibrium thermometer show that the clinopyroxene in fine-grained biotite gabbro crystallized from 946?to 1169?.The crystallization temperature of clinopyroxene in the pegmatic hornblende biotite gabbro of the Qingpi intrusion is 817?-1005?.The crystallization temperature of clinopyroxene in the alkaline granite of Qingpi intrusion is 959?-978?.The pyroxene in pegmatic hornblende biotite gabbro of the Qingpi intrusions has the lower crystallization temperature.It is consistent with the hydrous magma environment.The presence of water rich fluid reduces the crystallization temperature of clinopyroxene.The hornblende all-aluminum barometer calculates that the fine-grained biotite gabbro in the Qingpi intrusions fromed from 0.52kbar and 3.82kbar,and depth is 6.65km.The pressure of pegmatic hornblende biotite gabbro in the Qingpi area is between 0.69kbar and 1.61kbar,and the crustal depth is 4.72km.The pressure of the alkaline granite in the Qingpi area is between 0.62kbar and 1.04kbar,and the crustal depth is 3.53km.(3)The water content of the initial magma of the Qingpi intrusions is between5.44%and 9.65%.The average water content is 7.91%and the water content is much higher than general mafic magma.The ratio of H₂O/CO₂ in the fluid is 4.8,and the presence of the fluid diluted the magma.So the viscosity of the magma reduced,so that the path of the magma ascending is relatively long,reaching an emplacement depth of3-7 kilometers in the crust.(4)The partial melting La/Sm-Sm/Yb simulation of peridotite shows that Medium-fine-grained biotite gabbro is formed by partial melting of 1%-3%of mantle peridotite composed of 68%garnet peridotite and 32%spinel peridotite.The pegmatic hornblende biotite gabbro is equivalent to 0.7%-1%partial melting of the mantle peridotite composed of 63%garnet peridotite and 37%spinel peridotite.It is formed by the late fluid-rich residual melt crystallization of medium-fine-grained biotite gabbro.(5)The simulation results of MELTS software show that The magma system in Miyi area cooled down to 1192?and reached the liquidus and began to crystallize.The CO₂ and H₂O fluids played an important role in the mineralization process in Panxi area.