通化集安群石榴子石和黑云母微区化学成分特征及其对变质作用p-T-t轨迹的指示意义

集安群片麻岩中石榴子石和黑云母接触带两侧边缘广泛发育Fe－Mg交换反应所形成的扩散环带，但晶体内部各自保持变质峰期的成分，中温带石榴子石可保留生长环带。经微区化学成分详细研究后，正确运用Grt－Bt温度计获得进变质阶段，变质高峰期和修期后Fe－Mg交换反应停止时的温度条件。按石榴子石和斜长石的微区钙含量变化确定了峰期和退变质阶段压力。据此建立起逆时针形式的变质作用p－T－t轨迹，反映该区早元古代陆壳内裂陷带的闭合过程。

INTRACRYSTALLINE VARIATIONS IN CHEMICAL COMPOSITION OF GARNET AND BIOTITE FROM THE JI'AN GROUP OF TONGHUA DISTRICT AND ITS SIGNIFICANCE AS AN INDICATOR OF METAMORPHIC PTt PATH

Garnet and biotite from the Ji'an Group gneisses are characterized by extensive,but narrow diffusion zoning in the edge area on both sides along their contact boundary. But their equilibrium compositions at the metamorphic peak stage are usually maintained in the extensive interior of many grains of these two minerals. Garnet with growth zoning is also found in rocks of the kyanitezone. In the light of detailed investigation of intracrystalline compositional variations of Grt and Bt,the temperatures at the progressive stage,peak and post-peak metamorphic stage were determined by Grt-Bt geothermometry. Furthermore,the pressures at the peak and regressive metamorphic stages can also be calculated in terms of variations in Ca content from the core to the edge within the c0existi0n Grt and Pl. On this basis,the metamorphic p-T-t path of the counterclockwise type was constructed,which reflects the closing process of the ensialic rift belt in this region during the Early Proterozoic.