青藏高原北缘火山岩中辉石岩包体研究

摘要

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.%青藏高原北缘可可西里鲸鱼湖、雄鹰台、双泉子火山岩中含有辉石岩包体，其主要矿物组成为单斜辉石和斜方辉石。辉石的化学成分与国内外幔源包体－橄榄岩和辉石岩中的类似，与麻粒岩中的明显不同；辉石温压计计算结果表明，辉石形成的温度为1 101～1 400 ℃，压力为30×108～60×108 Pa，结合岩浆动力学计算结果，推测岩浆的来源深度大于150 km，这与地球物理研究得出本区地下深处存在低速层的结果相吻合。