柴北缘都兰地区含石榴石、蓝晶石片麻岩的变质演化历史  

Metamorphic evolution of garnet-and kyanite-bearing paragneiss in Dulan area of the North Qaidam Mountains, western China

作　　者：于胜尧[1] 张建新[1] 宫江华[1] 李云帅[1] 

机构地区：[1]大陆构造与动力学国家重点实验室中国地质科学院地质研究所,北京100037

出　　处：《岩石矿物学杂志》2014年第3期441-457,共17页Acta Petrologica et Mineralogica

基　　金：自然科学基金青年基金资助项目(41202037)

摘　　要：在柴北缘超高压变质带东段,新识别出一个高压麻粒岩单元,其主要的岩石组合包括基性（长英质）高压麻粒岩、花岗质片麻岩、富铝质片麻岩（片岩）、石榴角闪岩和英云闪长岩.岩相学和变质反应序列、矿物化学和温压估算结果表明,蓝晶-石榴-黑云-二长片麻岩共经历了4阶段的变质演化：Ⅰ早期进变质阶段,以石榴石核部发育的黑云母、白云母、斜长石和石英等矿物包裹体为特征;Ⅱ峰期高压麻粒岩相阶段,矿物组合为石榴石＋蓝晶石＋条纹长石＋斜长石＋石英,金红石Zr温度计和GASP压力计限定其峰期温压条件为：t=800～840℃和p=1.4～1.6GPa;Ⅲ高角闪岩相退变质阶段,矿物组合为石榴石（边部）＋黑云母＋长石＋石英;Ⅳ晚期低角闪岩相-绿片岩相退变质阶段,以蓝晶石周围出现的Ms＋Pl±Zo和Mrg＋ Qtz±Ms±Pl后成合晶为特征.锆石LA-ICP-MS U-Pb定年结果指示高压麻粒岩相变质时代为431Ma.蓝晶-石榴-黑云-二长片麻岩具有顺时针的pt演化轨迹,与基性高压麻粒岩形成于相同的动力学过程.A high-pressure granulite unit was recognized in Dulan area at the eastern end of the North Qaidam UHP metamorphic belt.The HP granulite unit comprises mafic （felsic） HP granulite,granitic gneiss,pelitic schist （gneiss）,garnet amphibolite and tonalite.Based on the petrographic features and metamorphic reaction,mineral chemistry and p-t calculations,the authors divided the paragneiss into four metamorphic stages：Stage I,which is the pre-peak prograde metamorphic stage characterized by biotite,muscovite,plagioclase and quartz inclusions within the core of zoned garnet porphyroblasts; Stage Ⅱ,the peak HP granulite-facies metamorphic stage,which is characterized by the mineral assemblage of garnet ＋ kyanite ＋ ternary-feldspar ＋ plagioclase ＋ quartz,with peak p-t conditions of t =800～840℃ and p =1.4～ 1.6 GPa; Stage Ⅲ,the initial decompressional retrogression began at the high amphibolite-facies stage characterized by garnet ＋ biotite ＋ plagioclase ＋ quartz; Stage Ⅳ,final retrogression under greenschist-facies conditions was developed at shallow crustal levels,characterized by the existence of Ms ＋ Pl ± Zo and Mrg ＋ Qtz± Ms± Pl assemblages around kyanite.Zircon LA-ICP-MS U-Pb dating yielded peak HP granulite-facies metamorphic age of 431 Ma.The combination of petrographic textures,mineral compositions and thermobarometric data defined a single clockwiseP-t path for the Dulan paragneiss,similar to that of HP mafic granulite.

关 键 词：柴北缘 都兰 副片麻岩 变质演化 

分 类 号：P588.345[天文地球—岩石学]