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南阿尔金尤努斯萨依花岗质高压麻粒岩的发现及其地质意义 被引量:7

Discovery of the high pressure granitic granulite in South Altyn and it's geological significance
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摘要 南阿尔金尤努斯萨依地区首次发现一套高压麻粒岩相特征矿物组合的含蓝晶石石榴子石的花岗质片麻岩,其矿物组合为Grt+Ky+Per(+Ksp)+Ru+Q。依据矿物内部一致性热力学数据,基于THERMOCALC 3. 40程序平台,计算出P-T视剖面图,并结合矿物等值线、矿物组合稳定域及三元长石温度计等,确定其早期变质温压条件为T=970~1010℃,P=23. 2~25. 3kbar,达到了榴辉岩相变质条件。同时,根据岩相学观察获得的矿物共生组合与矿物变质显微结构以及P-T视剖面图,可识别出该岩石在早期变质之后还经历了以矿物组合Grt+Ky+Per(+Ksp)+Pl+Ru+Q为代表的麻粒岩相、以及Grt+Ky+Ksp+Pl+Bi+Ru+Ilm+Q为代表的麻粒岩-高角闪岩相和以Ky+Ksp+Pl+Q+Bi+Mu+Ru+Ilm为代表的角闪岩相三期退变质作用,它们共同构成了一个顺时针型降温降压的退变质P-T演化轨迹,指示出与大陆俯冲-深俯冲相关的高压变质事件和俯冲碰撞后的折返事件。利用LA-ICP-MS进行的锆石原位微区U-Pb定年和微量元素分析表明,该高压岩石峰期变质年龄497. 8±2. 7Ma,与南阿尔金地区已发现的高压-超高压岩石的峰期变质时代完全一致,表明它们应属同一变质岩带;其原岩形成时代为900. 2±4. 1Ma,与南阿尔金已报道的正变质的高压-超高压岩石原岩的形成时代基本一致,指示它们可能具有相同的原岩属性。这套花岗质高压麻粒岩的确定为进一步约束南阿尔金早古生代高压-超高压变质岩带的时空分布规律提供了新的限定。 Kyanite-garnet-bearing granitic gneiss is first discovered in Younusisayi area of the South Altyn Tagh. The peak metamorphic assemblage is Grt + Ky + Per( Ksp) + Ru + Qz,which represents a typical high pressure granulite-facies metamorphic assemblage. Mineral relationship,phase equilibria modeling with pseudosections calculated using THERMOCALC 3. 40 and ternary feldspar thermometer constraints the peak metamorphic stage under the eclogite-facies conditions of T = 970 ~ 1010℃ and P = 23. 2 ~25. 3 kbar. Three retrograde metamorphic mineral assemblages are identified by microstructure, mineral relationship and P-T pseudosections,the granulite facies stage is recorded by mineral assemblage of Grt + Ky + Per( Ksp) + Pl + Q + Ru,granulite to high amphibolite-facies mineral assemblage is Grt + Ky + Ksp + Pl + Q + Bi + Ru + Ilm,and the low amphibolite facies metamorphic assemblage is Ky + Ksp + Pl + Q + Bi + Mu + Ru + Ilm. The P-T evolution of the granitic gneiss is characterized by a clockwise P-T path with pressure and temperature decrease,suggesting a tectonic event associated with continental deep subduction and exhumation.LA-ICP MS U-Pb dating reveal the protolith age of 900. 2 ± 4. 1 Ma and the peak metamorphic age of 497. 8 ± 2. 7 Ma. The peak metamorphic and protolith age of Younusisayi granitic gneiss are consistent to HP/UHP metamorphic rocks from the South Altyn Tagh,indicating they belong to the same HP/UHP metamorphic zone and have similar protolith nature. The confirmation of Younusisayi eclogite-facies granitic gneiss provides new restriction to the spatial and temporal distributions of Early Paleozoic HP-UHP rocks in the South Altyn Tagh.
作者 马拓 刘良 盖永升 王超 康磊 廖小莹 朴常完 张魁 MATuo;LIULiang;GAIYongSheng;WANGChao;KANGLei;LIAOXiaoYing;PAKSangWan;ZHANGKui(State Key Laboratory of Continental Dynamics,Department of Geology,Northwest University,Xi'an 710069,China)
出处 《岩石学报》 SCIE EI CAS CSCD 北大核心 2018年第12期3643-3657,共15页 Acta Petrologica Sinica
基金 国家自然科学重点基金项目(41430209) 国家重点基础研究发展计划项目(2015CB856103) 国家自然科学群体和面上基金项目(41421002、41602052、41672187) 中国人民武警黄金部队区域地质矿产调查项目(203140061) 西北大学大陆动力学国家重点实验室自主研究重点课题联合资助.
关键词 花岗质高压麻粒岩 变质P-T演化 大陆俯冲 尤努斯萨依 南阿尔金 High pressure granitic granulite P-T evolution Continental subduction Younusisayi South Altyn Tagh
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