豫南中温榴辉岩中角闪石的变质演化

Metamorphic Evolution of Amphiboles in Medium Temperature Eclogite from Southern Henan

在该区中温榴辉岩的各个演化阶段中，出现了不同成分的角闪石。石榴石环带及其核部的角闪石等矿物包裹体记录了前榴辉岩阶段及其进变质演化的特征。在榴辉岩阶段晚期，蓝闪石稳定出现，其成分环带反映了后期压力降低的连续过程；角闪石－斜长石后成合晶为石榴石和绿辉石的退变质产物；退变质后期，钙质闪石大量出现。角闪石的矿物组合及其成分变化，反映了中温榴辉岩的顺时针变质演化过程．

Microtextural relations and mineral compositions indicate that medium-temperature eclogite in southern Henan underwent a clockwise P-T path.A prograde evolutionary stage of the eclogite is recorded by composition zoning and inclusions in garnet. The eclogitic event produced the assemblage of garnet, omphacite,rutile and coesite. The composition zoning of matrix eclogitic amphibole (Amp 2) reveals that the subsequent evolution of the eclogitic factes must have experienced a late reequilibration under reduced pressure. The formation of Amp-P1 symplectite represents the early result of the destabilization of omphacites and granets in the amphibolite factes. Subsequent retrogression resulted in the complete breakdown of omphacite recorded by amphibole growth, with no relict of the high pressure assemblage preserved.