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Based on electron probe analyses of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil lithodistricts, Qinghai|Xizang plateau, the forming conditions including the temperature and pressure of those rocks are studied in this paper. According to the thermodynamic calculation results of mineral|melt equilibrium, the depth of the asthenosphere superface (about 75-130 km) for the northern part of the Qinghai|Xizang plateau during the Cenozoic is suggested. Finally, this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai|Xizang plateau mainly consist of shoshonite series. Their forming temperature is 630-1039℃ and forming pressure is between 2.3-4.0 GPa. The rocks were formed in the intracontinental orogenic belt, of which the primary magma was originated from a particular enrichment upper mantle and accreted crust|mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite.
Based on electron probe analyzes of the minerals and bulk composition of the Cenozoic volcanic rocks from Yumen and Hoh Xil lithodistricts, Qinghai | Xizang plateau, the forming conditions including the temperature and pressure of those rocks are studied in this paper. According to the thermodynamic calculation results of mineral | melt equilibrium, the depth of the asthenosphere superface (about 75-130 km) for the northern part of the Qinghai | Xizang plateau during the Cenozoic is suggested. Finally, this paper indicates that the Cenozoic volcanic rocks in the northern part of the Qinghai | Xizang plateau mainly consist of shoshonite series. Their forming temperature is 630-1039 ° C and forming pressure is between 2.3-4.0 GPa. The rocks were formed in the intracontinental orogenic belt, of which the primary magma was originated from a particular enrichment upper mantle and accreted crust | mantle belt or directly from asthenospheric superface as a result of partial melting of pyrolite .