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  

Petrographic features and metamorphic evolution of pumpellyite_bearing eclogite in Uzkaya Salma area of the Belomorian mobile belt, Russia

作　　者：齐云飞[1] 张立飞[1] 余黄露 

机构地区：[1]北京大学地球与空间科学学院,造山带与地壳演化教育部重点实验室,北京100871

出　　处：《岩石矿物学杂志》2016年第1期52-64,共13页Acta Petrologica et Mineralogica

基　　金：国家自然科学基金项目(40821002)~~

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。The pumpdlyite 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. Pumpdlyite 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 geothermo- barometers, the authors divide the metamorphic evolution of pumpdlyite-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 H, 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 decom- pressional 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 condi- tion of amphibolites-facies and is characterized by the mineral assemblage of hornblende ＋ plagioclase ± biotite ＋ quartz, with p-T con

关 键 词：含绿纤石榴辉岩 岩石学特征 变质演化 Uzkaya Salma地区 白海活动带 

分 类 号：P588.3[天文地球—岩石学]