摘要
西南天山蓝片岩的变质作用pTDt轨迹显示进变质作用为快速升压过程、退变质作用为近等热降压过程。自俯冲杂岩进入俯冲带到形成蓝片岩后抬升并出露于造山带,变质作用经历了浊沸右相(415Ma?)→硬柱石-蓝闪片岩相(408Ma?)→蓝闪绿片岩相(345Ma)→绿片岩相(314Ma)连续渐变演化的过程。蓝片岩中现存主要蓝闪绿片岩相矿物组合并非峰期变质矿物组合。造山运动晚期的大规模韧性推覆作用促成蓝片岩快速抬升并出露于造山带。
The blueschist belt, extending for about 300 km from Changawuzhi to theupper Kokesu river valley along the southwestern Tianshan Mountains, consistsof blueschists, greenschists and minor amounts of ophiolitic thrust slices and lensesof marbleised on limestones, of which blueschists occur. There are two kinds of blueschists, metabasic volcanic rocks and metasedimentary rocks. The principalminerals making up blueschists are glaucophanic amphiboles, garnet, albite, phen-gite, epidote, chlorite, quartz and so on. The metamorphic pTDt path of blueschists shows that the progressive meta-morphism is a process of rapid pressure increase and that the retrogressive meta-morphism is a process of nearly isothermal decompression. The pTDt path alsoreveals that the metamorphism underwent a continuous gradual evolution processof laumontit facies (415 Ma?)→lawsoniteglaucophane schist facies (408 Ma?)→glaucophane greenschist facies (345 Ma)→greenschist facies (314 Ma), from theentrance of the paleosubduction complexes into the deep part of the subductionzone to uplift the blueschists and outcropping in the orogenic belt. The principal-stage glaucophane greenschist facies mineral assemblages, preserved in blueschistsare not the peak-stage metamorphic mineral assemblages, but are The mineralassemblages of the early stage of retrogressive metamorphism. The largescale duc-tile overthrusting and rapid denudation led to rapid uplift of blueschists thatunderwent greenschist facies retrogressive metamorphism, so the glaucophanegreenschist assemblages could be preserved and exposed in the orogenic belt duringthe later orogenesis.
出处
《地质论评》
CAS
CSCD
北大核心
1994年第6期544-553,共10页
Geological Review
基金
国家自然科学基金(48970143)
地矿部行业基金(89036)
国家三○五项目(8590206)
