超高压榴辉岩中绿辉石组构和变形机制研究进展

Proceeding of Research on Fabric and Deformation Mechanisms of Omphacite in Ultra-high Pressure Metamorphic Eclogite

榴辉岩中绿辉石晶格优选方位(LPO)类型主要有S型(压扁型)组构、L型(收缩型)组构、L-S中间型组构、退火型组构,其中L型和S型组构是绿辉石在超高压岩石中最发育的组构类型。矿物组构的产生与变形机制密切相关,目前还无法解释绿辉石LPO产生和变化的原因。对天然绿辉石变形机制的最新研究进行了评述,包括位错蠕变产生变形绿辉石LPO的传统观点,以及扩散蠕变伴随晶体各向异性生长和空间群转换两种新观点。使用费氏台对大别山双河地区榴辉岩中的绿辉石组构进行了测量,并用电子背散射衍射技术(EBSD)对测量结果进行了验证。结合榴辉岩的显微构造和绿辉石组构特征对大别山双河超高压榴辉岩中绿辉石的变形机制进行了初步探讨,认为其变形机制以位错蠕变为主。

The reported LPO(lattice preferred orientation) types of omphacite in eclogite are mainly: S-type/flattening fabrics, L-type/constriction fabrics, composite fabrics between L- and S-type, annealed fabrics, among which L- and S-types contain the two most developed kinds in ultra-high pressure metamorphic rocks. Until now, the variation of LPO pattern of omphacite in eclogite and its relationship with deformation mechanism have not been understood well by plasticity models based on dislocation glide on the known slip systems in clinopyroxene. The paper summarizes a new proceeding of the research on natural deformed omphacite fabrics and its deformation mechanisms. Except for traditional viewpoint of dislocation creep, it also suggests two new ideas of diffusive creep with concomitant anisotropic growth and transformation of space group. Fabrics of omphacite in eclogite from Shuanghe area, Dabie Mountains, were measured by U-stage and one result was validated by EBSD (electron backscattered diffraction) technique. Meanwhile,combined with fabrics of omphacite and microstructure of eclogite, it discusses preliminarily deformation mechanisms of clinopyroxene in UHP metamorphic eclogite from Shuanghe area. Dislocation creep may be the dominate deformation mechanism and further research is necessary to determine whether other mechanisms,e.g. diffusion creep are involved in the deformation of eclogite.