滦平小白旗角闪石榴斜长二辉麻粒岩变质作用P-T轨迹及构造意义

The P-T Path of Two-Pyroxene Granulite in Luanping Area and Its Tectonic Implication

在桑干构造带,滦平地区基性麻粒岩主要由石榴石、角闪石、单斜辉石、斜方辉石、斜长石、石英六种矿物组成。岩相学特征表明其经历了三个期次的变质作用:峰期高压麻粒岩相(M1):代表性矿物是石榴石+单斜辉石+石英。中压二辉麻粒岩相(M2):代表性矿物为斜方辉石+单斜辉石+斜长石±石英。角闪岩相(M3):代表性矿物为斜长石+角闪石。使用传统地质温压计估算出三个期次的温度压力分别为636℃~719℃,7.9~11 kbar;775℃~861℃,5.6~7.1 kbar;649℃~653℃,4.2~4.3 kbar。构建出的变质作用P-T轨迹为顺时针型,峰后升温降压的特点与碰撞造山的地质背景相对应。

The basic granulite in Luanping area,Sanggan structure zone is mainly consists of six minerals:garnet,hornblende,plagioclase,clinopyroxene,orthopyroxene and quartz.Petrography characteristics reflect that it underwent three metamorphic stages:the peak high-pressure granulite-facies assemblage(M1)is defined by garnet+clinopyroxene+quartz;the medium-pressure granulite-facies metamorphism(M2)is composed of plagioclase+orthopyroxene;the amphibolite facies stage(M3)is characterized by plagioclase and hornblende.Using geological temperature-pressure indicator,the temperature and pressure conditions of different metamorphic stages are estimate roughly to be 636-719℃,7.9-11 Kbar;775-861℃,5.6-7.1 KBar,649-653℃,4.2-4.3 Kbar,respectively.combined with petrography characteristics,a clockwise P-T path characterized by decompression with a temperature decrease can be reconstructed.In addition,we propose that the two-pyroxene granulite form this region formed drring collisional orogcny.