秦岭-大别榴辉岩中绿辉石的显微结构特征

Microstructural Characteristics of Omphacite in Eclogite from The East Qinling and Dabie Mountains

本文对秦岭-大别山高压超高压变质带中的绿辉石进行了高分辨电镜研究。绿辉石的超微结构以P2有序结构为主,其次为P2/n次有序结构和C2/c无序结构。并观察到绿辉石的P2或P2/n结构的反相畴界及π层错;C2/c结构中1/2(a+b)或1/2<110>的反相畴结构;有序绿辉石中的位错斜壁和低角度亚晶界;绿辉石的有序无序结构的相转变及晶畴结构。由电子衍射和高分辨像的分析结果表明,三个不同地区的绿辉石是在高压超高压条件下形成。反相畴的大小可作为变质温度和地质年代的重要标志。上述超微结构信息充分揭示了秦岭-大别山高压超高压变质带构造的本质特征和演化规律。

Microstructural characteristics of omphacite from the high-pressure and ultrahigh-pressure metamorphic belt in the East Qinling and Dabie Mountains were investigated by electron diffraction analysis and high resolu- tion image observation. It has been found that the principal structural form of omphacite is the ordered structure P2,somewhat ordered structure P2/n and disordered structure C2/c. The ultrastructures of omphacite include antiphase domain boundary and π faults in the P2 or P2/n structures,the 1/2(a+b) or 1/2 <110>antiphase domain structure in the C2/c structure, the dislocation tiltwalls and lowangle subgrain boundaries of P2 or P2/n structures, domain structure of translation and phase transformation of order disorder structures. The electron diffraction and high resolution images show that omphacite in eclogite formed under the condition of highpressure and ultrahigh-pressure. The size of antiphase domain can be regarded as an important indicator of metamorphic temperature and the geological time. The characteristics and evolution of the high-pressure and ultrahigh-pressure metamorphic belt structure in the East Qinling and Dahie Mountains may he revealed from the ultrastructures of omphacite.