西垄玄武质岩石中的橄榄岩类包体、捕虏晶以及巨晶的矿物化学研究

浙江衢县西垄和金华龙游一带分布有许多第三纪的霞石玄武岩、玻基橄辉岩、橄辉玢岩和超基性火山角砾岩岩体和岩脉。它们富含橄榄岩类包体和来源于破碎的橄榄岩包体的各种捕虏晶(橄榄石、斜方辉石、透辉石和石榴石)。此外,还常含有富铝普通辉石、石榴石和钛铁矿巨晶。本文试图在大量的单矿物分析数据基础上,讨论橄榄岩类包体、捕虏晶以及巨晶的矿物化学及其形成条件。关于橄榄岩包体的主要元素和微量元素地球化学以及成因岩石学的研究,笔者已在另一篇论文中专门论述(从柏林和张儒瑗,1983),这里不再重复。

MINERALOGY OF PERIDOTITIC INCLUSIONS,XENOCRYSTS AND MEGACRYSTS IN BASALTIC ROCKS FROM SILONG,QU COUNTY,ZHEJIANG PROVINCE

The Tertiary nepheline basalt,limburgite and ultrabasic breccia widely occur in the region from Qu County to Jinhua County as small body and dyke.There are abundant perido-titic inclusions,xenocrysts derived from unaggregated inclusions and high pressure megacry-sts (garnet,aluminous augite and Mg-bearingilmenite) within these basaltic rocks.This paper presents 30 new chemical analyses of separated minerals,and describes their mineral chemistry and P-T conditions of crystallization.As comparing with the same minerals of peridotitic inclusions from some localities in North China,the minerals studied here have more refractory nature,namely they are characterized by relatively enriching in Mg and depleting in fusible components (Olivine,Fo 90.3 -93.5 with an average 91.3; Orthopyroxene,En 90.5-93.7 with an average 91.6; Diop-side,100Ca/(Ca+Mg+Fe) 41-42.1 with an average 41.7; Garnet,100Mg/(Mg+Fe²⁺) 89.2-89.8,TiO₂ 0.1 wt.% and CaO 4-5 wt.%.The estimation of the equilibrium P-T conditions of the ultramafic inclusions shows that garnet and spinel peridotitic inclusions equilibrated at about 1200℃,28 Kb,and 1000℃-1200℃,20-24 Kb,respectively.The origin of Al-augite and garnet megacrysts have been discussed in this paper as well.It may be suggested that they are near liquidus phases of an alkalic basaltic magma at high pressure.