西南天山变质俯冲杂岩带的内部结构——来自木扎尔特剖面的启示  

Internal structure of deeply subducted accretionary complex in southwestern Tianshan:Implications from the Muzhaerte section

作　　者：姜雪薇 吕增[1] JIANG Xue-wei;LU Zeng(The Key laboratory of Orogenic Belts and Crustal Evolution,School of Earth and Spare Sciences,Peking University,Beijing 100871,China)

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

出　　处：《岩石矿物学杂志》2021年第6期1181-1188,共8页Acta Petrologica et Mineralogica

基　　金：国家重点研发计划(2019YFA0708501);国家自然科学基金项目(42072075)。

摘　　要：西南天山高压-超高压变质带是世界上少有的经历深俯冲的增生杂岩带,是古天山洋向北俯冲的结果。针对该俯冲杂岩带内部结构的研究目前仍存在争论。本文以木扎尔特地区一条长约4 km的南北向剖面为例,对西南天山高压-超高压变质带的野外特征、矿物学和变质演化研究进行了综述。目前的研究表明,木扎尔特地区存在超高压和高压两类硬柱石榴辉岩,但绝大部分都经历了强烈的退变质和变形改造,被蓝片岩相或绿片岩相矿物组合取代。这些变基性岩在空间上构成北部和南部两个榴辉岩带,二者为构造接触。木扎尔特超高压硬柱石榴辉岩与其围岩经历相似的峰期压力构成西南天山超高压带的西端。与东侧阿克牙孜地区超高压榴辉岩相比,它们在变形特征、岩石组合和变质演化方面表现出一定的独特性,很可能说明深俯冲板片在折返过程中沿构造带走向存在差异变质-变形演化。这些基础研究对全面认识冷俯冲增生杂岩带的变质演化及其俯冲和折返的地球动力学机制具有重要意义。The southwestern Tianshan high-and ultrahigh-pressure metamorphic belt is a rare example of metamorphosed accretionary mélange exhumed from great depths,as a result of the closure of the paleo-Tianshan Ocean.The internal structure of the subduction complex is still controversial.Taking a~4 km-long N-S cross section in the Muzaerte area as an example,this paper summarizes the field occurrences,mineralogy and metamorphic evolution of the southwestern Tianshan high-and ultrahigh-pressure metamorphic belt.These studies suggest that there expose two types(i.e.,UHP and HP)of lawsonite eclogites,but most of them were strongly retrogressed and deformed at blueschist-and greenschist-facies conditions.These metabasic rocks constitute two eclogite belts,including northern and southern,that are separated by a fault.The Muzhaerte UHP lawsonite eclogites and their host rocks experienced similar peak metamorphism,constituting the western termination of the UHP metamorphic belt of southwestern Tianshan.Compared with the eastern Akeyazi UHP eclogites,they are different in terms of deformation features,rock assemblages and metamorphic experiences,probably indicating that deeply subducted slab occurred different metamorphic and transform evolution along-strike variations of tectonometamorphic processes during exhumation.These results are fundamental to unravel the metamorphic evolution of subducted accretionary mélange and related geodynamics during slab subduction and uplift.

关 键 词：超高压俯冲杂岩 变质带温压结构 硬柱石榴辉岩 木扎尔特 西南天山 

分 类 号：P588.3[天文地球—岩石学]