青藏高原新生代火山岩矿物化学及其岩石学意义

This paper deals with the features of mineralchemistry about olivine, pyroxene, feldspar, sanidine megacryst and garnet megacryst fromCenozoic volcanic rocks, Qinghai-Tibet plateau. The forming condition includingtemperature and pressure of the volcanic rock series is also studied. The results showthat olivine belongs to forsterite (Fo=81—85) and clinopyroxene is rich in TiO₂(1.06%—1.74%). Especially the sanidine megacryst is optical homogeneous. There are notzonal texture, exsolution texture and twin crystal. It is low in ordering degree andbelongs to K-sanidine. The garnet megacryst mainly consists of Alm and Pyr, whichcrystallization depth resembles the depth of middle crust. The mineral chemistry, majorelement and isotopic features indicate that of the Cenozoic volcanic rocks in the northpart of the Qinghai-Tibet plateau mainly consists of shoshonite series formed in theintracontinental orogenic belt, which primary magma originated from a particularenrichment upmantle and accreted crust-mantle mixed belt.