Pyroxenite Xenolith in the Volcanic Rocks from North Tibet
青藏高原北缘火山岩中辉石岩包体研究

The pyroxenite xenolith in the volcanic rocks from Hohxil, north Tibet, consists of clinopyroxenes and othopyroxenes. Mineral chemically these pyroxenes are similar to mantle enclaves including peridotite and pyroxenite from China and abroad, and different from ones of granulites. The temperatures and pressures of forming pyroxenes are in ranges of 1 101～1 400 ℃（averaged 1 250　℃） and 30×108～60×108Pa（averaged 46×108Pa）based on the thermobarometer of Mercier(1980), respectively. Combined with magma dynamics we deduced that magma was derived from the mantle with the depth of more than 150 km, which is fit in with geophysical conclusion that showed the low-velocity zone existed in the mantle under 150 km.