柴北缘鱼卡榴辉岩的pT演化历史
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P588.3

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国家自然科学基金资助项目(40272095,40472102),中国地质调查局地质调查资助项目(200413000031,200313000058),国土资源部百名优秀青年科技人才计划资助


pT evolution of the Yuqia eclogite in northern Qaidam Mountains
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    摘要:

    鱼卡榴辉岩位于柴北缘HP/UHP变质带的西段,榴辉岩呈透镜状或似层状分布在变质泥质岩、花岗质片麻岩及少量大理岩中,主要由石榴石和绿辉石组成,具有含量不等的多硅白云母、角闪石、黝帘石(斜黝帘石或绿帘石)、金红石和石英等。岩相学和矿物化学研究显示榴辉岩经历了3期与俯冲和折返作用有关的变质演化阶段:(1)前榴辉岩相进变质阶段,榴辉岩矿物组合为石榴石(核) 绿帘石 斜长石 角闪石,以包体的形式保存于具有生长环带的石榴石核部,形成的温压条件为p=1.06~1.11GPa,t=560~577℃;(2)榴辉岩相变质阶段,以绿辉石、多硅白云母等矿物围绕石榴石定向分布为特征,其矿物组合为石榴石(边) 绿辉石 多硅白云母±黝帘石,温压估算获得榴辉岩相的变质条件为p=2.35~2.52GPa,t=610~680℃;(3)后榴辉岩相变质阶段,矿物组合为石榴石 角闪石 斜长石,主要存在于围绕榴辉岩透镜体分布的退变榴辉岩(角闪石化榴辉岩)中,形成的温压条件为p=1.09±0.12GPa,t=635±44℃。研究结果显示榴辉岩的pT轨迹具有“发卡”型特点,表明鱼卡榴辉岩经历了快速俯冲和折返的演化历史。

    Abstract:

    In the Yuqia area within the western segment of northern Qaidam Mountains, eclogite lenses and interlayers are enclosed within metapelites, granitic gneisses and small amounts of marbles. Eclogite is composed of garnet and omphacite with varying amounts of amphibole, phengite, zoisite (clinozoisite or epidote), rutile and quartz. Petrography, mineral chemistry indicate that theeclogites record a three-stage evolution connected to Early Paleozoic burial and subsequent exhumation: (1) The prograde stage is composed of garnet cores and large amounts of mineral inclusions including amphibole, epidote and plagioclase. pT estimates give metamorphic conditions of 1.06~1.11 GPa and 560~577℃.(2) The eclogite facies stage is characterized by the assemblages of oriented omphacite, phengite, barroisite and zoisite around garnet porphyroblasts. The assemblages record peak conditions of 2.35~2.51 GPa and 610~680℃.(3) Retrograde assemblages are recognized in amphibolitized eclogite along the eclogite boudin margin. The assemblages of garnet, amphibole and plagioclase record retrograde conditions of 1.09±0.12 GPa and 630±44℃.It is inferred that there existed ahairpin-shaped p-Tpath, and all this suggests that the Yuqia eclogites underwent an evolutionary history of rapid burial and uplift.

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张建新 孟繁聪 杨经绥,2005,柴北缘鱼卡榴辉岩的pT演化历史[J].岩石矿物学杂志,24(4):245~254. ZHANG Jian_xin, MENG Fan_cong, YANG Jing_sui,2005,pT evolution of the Yuqia eclogite in northern Qaidam Mountains[J]. Acta Petrologica et Mineralogica,24(4):245~254.

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