钦杭结合带加里东期榴闪岩超高压变质作用研究  

Discussion on the ultrahigh-pressure metamorphism of Caledonian garnet amphibolite in the Qinzhou-Hangzhou joint belt

作　　者：姜杨[1] 陈志洪[1] 谭桂丽[1] 杨祝良[1] 周效华[1] 袁强 余明刚[1] 赵希林[1] 段政[1] 

机构地区：[1]南京地质矿产研究所,南京210016 [2]浙江省地质调查院,杭州311203

出　　处：《资源调查与环境》2015年第2期79-88,共10页Resources Survey & Environment

基　　金：中国地质调查局项目(项目编号:12120114005801和12120113065200);国家自然科学基金青年基金项目(项目编号:41002024)资助

摘　　要：对钦杭结合带首次发现的加里东期榴闪岩进行了详细的年代学、矿物学和变质作用研究。结果表明,榴闪岩的变质时代为454±4Ma,经历了早期角闪岩相进变质、中期榴辉岩相峰期变质和晚期角闪岩相退变质三个阶段,具顺时针P-T-t轨迹。早期角闪岩相进变质作用阶段的矿物共生组合为角闪石+斜长石+石英,温压条件分别为719℃~795℃和7.56Kpa^8.30Kpa;中期榴辉岩相峰期变质作用阶段的矿物共生组合为石榴子石+绿辉石(后期退变为透辉石+钠长石)±石英,温压条件分别为668℃~821℃和26.42Kpa^33.46Kpa;晚期角闪岩相退变质作用阶段的矿物共生组合为石榴子石+角闪岩+斜长石±石英(即榴闪岩),相应的温压条件分别为611℃~854℃和4.76Kpa^9.30Kpa。结合前人资料推断,区域内加里东期可能经历了榴辉岩相超高压变质→高温麻粒岩相退变质→角闪岩相退变质的演化过程。钦杭结合带首次厘定出加里东期超高压变质作用,表明华夏和扬子两大陆块碰撞拼合发生在加里东期。By studying on the chronology,mineralogy and metamorphism of Caledonian garnet amphibolite first discovered in the Qinzhou-Hangzhou joint belt,it is concluded that the garnet amphibolite,which possesses typical clockwise P-T-t path including amphibolite-facies prograde metamorphism in early stage,eclogite-facies（UHP）peak metamorphism in middle stage and amphibolite-facies retrogressive metamorphism in late stage,yields a metamorphic age of 454±4Ma.The mineral assemblage of the amphibolite-facies prograde metamorphism in early stage is amphibole（Amp）＋plagioclase（Pl）＋quartz（Qtz）with temperature of 719℃~795℃ and pressure of 7.56Kpa^8.30 Kpa,the eclogite-facies（UHP）peak metamorphism in middle stage has the mineral assemblage of garnet（Gt）＋ akmite（retrograde to diopside＋albite）±Qtz with temperature of 668℃~821℃and pressure of 26.42Kpa^33.46 Kpa,the amphibolite-facies retrogressive metamorphism in late stage is composed of Gt＋Amp＋Pl±Qtz with temperature of611℃~854℃ and pressure of 4.76Kpa^9.30 Kpa.Combined with the previous studies,it is proposed that the Qinzhou-Hangzhou joint belt had undergone evolutionary process of eclogite-facies（UHP）metamorphism,granulite-facies retrogressive metamorphism and amphibolite-facies retrogressive metamorphism in Caledonian.The first discovery of the Caledonian UHP metamorphism in the Qinzhou-Hangzhou joint belt indicates that the collision between Cathaysia and Yangtzs blocks occurred in Caledonian.

关 键 词：超高压变质 顺时针P-T-t轨迹 榴闪岩 加里东期 钦杭结合带 

分 类 号：P588.34[天文地球—岩石学]