黄镇低温榴辉岩中石榴石成分分带的扩散动力学研究

MODELING OF HUANGZHEN LOW-T ECLOGITE WITH DIFFUSION KINETICS THEORY

对南大别黄镇低温榴辉岩中不同粒径的石榴石颗粒所具有的不同化学成分分带进行研究,通过建立相应的扩散调整模型,运用扩散动力学的方法进行了模拟计算。结果表明该榴辉岩中石榴石经过峰期榴辉岩相变质之后,其成分环带经约23Ma的扩散调整形成现在的组分特征。黄镇榴辉岩在峰期变质之后曾经历的是一个约6℃/Ma冷却过程,该过程持续了约23Ma。黄镇榴辉岩不大可能与南大别超高压榴辉岩一样受到过超高压变质作用。

We determined the compositions of various sizes of garnets in so-called cold Huangzhen eclogites from Southern Dabie with electron microprobe, and observed that it shows intriguing zoning patterns. We find these zoning patterns can be interpreted by a relaxation diffusion mechanism. Using relaxation diffusion model, with the determined PT condition by means of traditional petrologic methods by others and numerically model of the profile's adjusting, the result suggests the adjustment of the smallest garnet in this study cost 23Ma until the process ceased. This means that the rocks of Huangzhen suffered an exhumation velocity about 6℃/Ma after the peak metamorphism. This result supports the idea that the Huangzhen eclogites did not experienced UHPM, and also provides important information on the tectonic mechanism for the mountain Dabie eclogites exhumation.