The P-T path and geological significance of low-pressure granulite-facies metamorphism in Muzhaerte, southwest Tianshan
The P-T path and geological significance of low-pressure granulite-facies metamorphism in Muzhaerte, southwest Tianshan
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作者：
Li Qian
在新疆西南天山木扎尔特地区首次发现了二辉麻粒岩和条格-席片麻岩。二辉麻粒岩中的特征矿物组合为Cpx-Opx-Bi-Hb-Pl-Q，Cord-Grt-Sill片麻岩中的特征矿物组合为Cord-Sill-Grt-Bi-Pl-Q。岩石学和矿物学研究表明，二辉麻粒岩和Cord-Grt-Sill片麻岩经历了典型的低压麻粒岩相变质作用。Cord-Grt-Sill片麻岩的变质演化可分为两个阶段：1。峰麻粒岩相阶段：T=681-705℃，P = 5。四比五8kbar; 2.退变质角闪岩相阶段：T = 571 - 637℃，P =4。七比五3kbar。西南天山木扎尔特低压麻粒岩相变质Cor-Grt-Sill片麻岩P-T轨迹以逆冲等压冷却（ACW-IBC）为特征，这是塔里木板块向伊犁-中天山板块俯冲过程中，下部岩浆板下侵入陆壳一侧陆源弧区的结果。根据岩石学研究、构造关系和形成时代，认为研究区低压麻粒岩相变质带与其南部高压-超高压变质带可能构成一对变质带。
Two-pyroxene granulite and Cord-Grt-Sill gneiss have been found for the first time in Muzhaerte, southwest Tianshan, Xinjiang. The chararcteristic 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-facies stage: T=681-705℃, P = 5. 4 - 5. 8kbar; and 2. retrograde amphibolite-facies stage: T = 571 - 637℃,P =4. 7 - 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 arc 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.