甘肃北山榴辉岩的变质历史

Metamorphic History of Eclogites from Beishan, Gansu Province

岩相学、矿物化学和变质条件的估算表明 ,甘肃北山榴辉岩经历了前榴辉岩相 ( 60 4～ 678℃、0 .89～ 1.0 5GPa)、榴辉岩相 ( 70 0～ 72 0℃、1.2～ 1.5GPa)、角闪岩相 ( 62 9℃、0 .63～ 0 .83GPa)和绿片岩相 (约 4 0 0℃、0 .3～ 0 .4GPa) 4个演化阶段。这一P T轨迹证明北山榴辉岩是塔里木板块与哈萨克斯坦板块在俯冲

Based on the study of petrography and mineral chemistry and the estimation of metamorphic conditions, the authors recognized four metamorphic stages in eclogites from Beishan, Gansu Province, western China. The earlier pre eclogite facies assemblage of Al rich amphibole + zoisite + quartz preserved in the garnet crystals was formed at 604～678 ℃ and 0.89～1.05 GPa. Eclogite facies metamorphism characterized by the assemblage of garnet + omphacite + quartz + rutile equilibrated under the condition of 700～720 ℃ and 1.2～1.5 GPa. The retrograde amphibolite facies stage produced paragenesis of amphibole + plagioclase + quartz + titanite at 629 ℃ and 0.63 ～0.83 GPa. The formation of greenschist facies metamorphism represented by actinolite + chlorite finally took place at about 400 ℃ and 0.3～0.4 GPa. This P T path implies that the crust was thickened abruptly, caused by subduction during the collision of Talimu and Kazakhstan plates, and the subsequent exhumation might be attributed to rapid tectonic uplift.