俄罗斯白海活动带Uzkaya Salma地区含绿纤石榴辉岩的岩石学特征及其变质演化
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国家自然科学基金项目(40821002)


Petrographic features and metamorphic evolution of pumpellyite-bearing eclogite in Uzkaya Salma area of the Belomorian mobile belt, Russia
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    摘要:

    俄罗斯白海活动带Uzkaya Salma地区榴辉岩中发现的绿纤石形成于榴辉岩化早期亚绿片岩相阶段。该绿纤石多以包体形式存在于退变榴辉岩的变斑晶石榴石矿物中,并与榍石、金红石、单斜辉石、绿泥石、绿帘石、石英等矿物伴生,极少量单颗粒绿纤石包裹在基质单斜辉石(透辉石)矿物中,呈浑圆状。绿纤石成分上属于铝绿纤石和铁绿纤石,其中以铝绿纤石为主。在详细的岩相学研究基础上,通过相平衡计算,结合矿物温压计计算结果,发现含绿纤石榴辉岩共经历了4阶段的变质演化:Ⅰ早期进变质阶段,以石榴石中的绿纤石+绿泥石+绿帘石+石英等矿物包裹体为特征,依据实验岩石学研究的矿物组合绿纤石+绿泥石+石英和铁绿纤石+绿帘石稳定域,估算该变质阶段温压条件t=160~320 ℃, p=0.2~0.8 GPa;Ⅱ峰期榴辉岩相阶段,矿物组合为石榴石+Di-Pl后成合晶推测的绿辉石+金红石±角闪石+石英,石榴石核部镁等值线和绿辉石硬玉分子等值线限定其峰期温压条件为t=725~740℃, p=1.4~1.5 GPa;Ⅲ 高压麻粒岩相退变质阶段,矿物组合为石榴石+透辉石+角闪石+斜长石+石英,石榴石-单斜辉石温度计和后成合晶中斜长石钙等值线限定该阶段的温压条件t=725~750℃, p=1.1~1.3 GPa;Ⅳ晚期角闪岩相退变质阶段,矿物组合角闪石+斜长石±黑云母 +石英,相平衡计算和角闪石-斜长石温度计限定温压条件为t=670~700℃,p=0.7~0.9 GPa。综上,确定了俄罗斯白海活动带Uzkaya Salma地区含绿纤石榴辉岩具有顺时针的p-T演化轨迹,峰期对应的地温梯度为15℃/km,俯冲进变质阶段经历了绿纤石-绿帘石相变质,由峰期榴辉岩相到退变质高压麻粒岩相具近等温降压的特征。研究表明,板块的"冷"俯冲作用在地球演化早期太古宙时期就可能出现了。

    Abstract:

    The pumpellyite in the eclogites from Uzkaya Salma area of the Belomorian mobile belt, Russia, was formed at the pre-eclogite stage under the condition of sub-greenschist facies. Pumpellyite occurs as inclusions in garnet porphyroblasts and is associated with titanite, rutile, clinopyroxene, chlorite, epidote and quartz. In addition, rare granulous pumpellyite occurs as isolated inclusions in the matrix diopside. According to the composition features of pumpellyite, pumpellyite mostly belongs to pumpellyite-(Al) and rarely belongs to pumpelltie-(Fe). According to the petrographic features and the calculation of phase equilibrium and mineral geothermobarometers, the authors divide the metamorphic evolution of pumpellyite-bearing eclogite into four stages: Stage Ⅰ, which is the pre-peak prograde metamorphic stage characterized by pumpellyite, chlorite, epidote, quartz inclusions within the garnet porphyroblasts, with p-T conditions being t=160~320℃, p=0.2~0.8 GPa according to the stable field of mineral assemblages of pumpellyite + chlorite + quartz and pumpellyite-(Fe) + epidote, based on experimental petrologic study. Stage Ⅱ, the peak eclogite-facies metamorphic stage, which is characterized by the mineral assemblage of garnet + omphacite (the symplectite of diopside and plagioclase) + rutile ± hornblende + quartz; the isopleths in garnet core and the Jd isopleths in omphacite reflect the metamorphic peak condition of 725~740℃ at 1.4~1.5 GPa for the rock. Stage Ⅲ, during which the initial decompressional retrogression began at the high granulite-facies stage characterized by garnet + diopside + hornblende + plagioclase + quartz; the garnet-clinopyroxene thermometer and An isopleths in plagioclase indicate that the p-T conditions t=725~750℃ and p=1.1~1.3 GPa. Stage Ⅳ, which is late retrogression under the condition of amphibolites-facies and is characterized by the mineral assemblage of hornblende+plagioclase±biotite+quartz, with p-T conditions t=670~700℃ and p=0.7~0.9 GPa according to the calculation of phase equilibrium and hornblende-plagioclase thermometer. In conclusion, the pumpellyite-bearing eclogite in Uzkaya Salma area of the Belomorian mobile belt, Russia, shows a clockwise p-T path and the corresponding geothermal gradient in the peak eclogite-facies metamorphic stage is 15℃/km. The initial pre-eclogite metamorphic evolution began under the condition of pumpellyite-epidote facies during subduction. The pumpellyite-bearing eclogite is characterized by isothermal decompression from the peak eclogite-facies to the high granulite-facies. The results obtained by the authors show that "cold" subduction of the plate might have occurred at the early stage of the evolution of the earth during Archean.

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齐云飞,张立飞,余黄露,2016,俄罗斯白海活动带Uzkaya Salma地区含绿纤石榴辉岩的岩石学特征及其变质演化[J].岩石矿物学杂志,35(1):52~64. QI Yun-fei, ZHANG Li-fei, YU Huang-lu,2016,Petrographic features and metamorphic evolution of pumpellyite-bearing eclogite in Uzkaya Salma area of the Belomorian mobile belt, Russia[J]. Acta Petrologica et Mineralogica,35(1):52~64.

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  • 收稿日期:2015-02-15
  • 最后修改日期:2015-05-28
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  • 在线发布日期: 2016-01-22
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