再论麻粒岩的分类命名

Further Discussion on the Classification and Nomenclature of Granulites

麻粒岩的变质作用必须达到麻粒岩相,但麻粒岩相岩石不都是麻粒岩。麻粒岩应具有花岗变晶结构和麻粒构造并含有紫苏辉石以及含>10％的斜长石。分类命名以实测的岩石实际矿物的百分含量为基础,采用长石类(斜长石±钾长石±石英)—无水铁镁矿物(紫苏辉石+(次)透辉石+石榴石等)—含水铁镁矿物(普通角闪石+黑云母)为三个顶点的三角图解进行。单矿物岩的矿物含量范围为90—100％。以斜长石(包括钾长石±石英)的30％、60％和90％来划分暗色、中色和浅色麻粒岩。麻粒岩和斜长角闪岩等(包括部分片麻岩)的分界从无水铁镁矿物和含水铁镁矿物连线的中点(即50％处)向三角图的长石顶角画一直线,据此共划分出麻粒岩和其他岩类共14种。

The metamolphic grade of granulites must reach to the granulite facies but not all the rocks of granulite facies are exclusively granulite. The granulite always contains some hypersthene and>10% of plagioclase and possesses the granoblastic texture and granulitic structure. Based on their mineral modal composition a further classification of the granulites is made in a triangular compositional diagram, with feldspar(plagioclase±orthoclase±quartz) —anhydrous ferromagnesian minerals (Hypersthene+diopside+garnet, etc)—hydrous ferromagnesian minerals(hornblende+biotite) as its three vertices. The 0-30, 30-60 and 60-100 percent of plagioclase (±orthoclase±qartz) contents are taken as the ranges of the melanocratic, mesocratic and leucogranulite, respectively. The mineral modal Composition of monomineral locks ranges from 90% to 100%. The distingction of granulites from plagioclase-amphibolite and gneises has set up and 14 granulites and related rocks have been subdivided.