新疆西南天山木扎尔特一带低压麻粒岩相变质作用P-T轨迹及其地质意义  

The P-T path and geological significance of low-pressure granulite-facies metamorphism in Muzhaerte, southwest Tianshan

作　　者：李强[1] 张立飞[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2004年第3期583-594,共12页Acta Petrologica Sinica

基　　金：国家基础科学发展规划项目(G1999075508);国家自然科学基金(40325005;40228003)和教育部高校青年教师奖励计划联合资助.

摘　　要：本文首次报道在新疆西南天山木扎尔特一带发现了二辉石麻粒岩和麻粒岩相变质的堇青石榴矽线石片麻岩。二辉石麻粒岩的矿物组合为单斜辉石-斜方辉石-黑云母-角闪石-斜长石-石英。堇青石榴矽线石片麻岩矿物组合为堇青石-矽线石-石榴石-黑云母-斜长石-石英。岩石学和矿物学特征表明它们是典型的低压麻粒岩相变质岩石,其变质作用经历了两期演化:a.峰期麻粒岩相变质,T=681～705℃,P=5.4～5.8kbar;b.峰后角闪岩相遇变阶段,T=571～637℃,P=4.7～5.3kbar。其变质作用P-T轨迹具有逆时针近等压降温(IBC)的特点,代表该地区可能为塔里木板块向伊犁-中天山板块俯冲过程中,在陆壳一侧所产生的陆源岩浆弧区域,由于受到下部岩浆热源的影响,在拉伸环境下出现低压麻粒岩相变质。通过分析低压麻粒岩相岩石与其南部高压-超高压变质带的大地构造位置和年代关系,我们认为该地区的低压麻粒岩相变质岩石可能与其南部的西天山高压-超高压变质带组成了双变质带。Two-pyroxene granulite and Cord-Grt-Sill gneiss have been found for the first time in Muzhaerte, southwest Tianshan, Xinjiang. The charareteristic mineral assemblages are Cpx-Opx-Bi-Hb-Pl-Q in two-pyroxene granulites and Cord-Sill-Grt-Bi-Pl-Q in Cord-Grt-Sill gneisses. Petrologic and mineralogical studies show that two-pyroxene granulite and Cord-Grt-Sill gneiss had undergone a typical low-pressure granulite facies metamorphism. The metamorphic evolution of Cord-Grt-Sill gneisses has been divided into two stages.. 1. peak granulite-faeies stage: T=681 similar to705degreesC, P = 5.4 similar to 5. 8kbar; and 2. retrograde amphibolite-facies stage: T=571 similar to 637degreesC, P = 4.7 similar to 5.3kbar. The P-T path of low-pressure granulite-facies metamorphic Cord-Grt-Sill gneisses in Muzhaerte, southwest Tianshan, is characterized by anticlockwise isobaric cooling ( ACW-IBC) resulting from the infection of lower magma underplate to the area of terrigenous are on the side of continental crust during the subduction of Tarim plate northward to Yili-Central Tianshan plate. Furthermore, it is proposed that low-pressure granulite facies metamorphic belt and its southern HP-UHP belt in the study area compose likely a paired metamorphic belt based on their petrological studies, tectonic relation and forming ages.

关 键 词：低压麻粒岩相 逆时针近等压降温P-T轨迹 双变质带 木扎尔特 西南天山 新疆 

分 类 号：P588.346[天文地球—岩石学]