不同应力途径下辉长岩的微破裂特征

OBSERVATION OF MICROCRACKS WITHIN GABBRO IN EXPERIMENTS ALONG VARIOUS STRESS PATHS

  • 摘要: 本文对济南辉长岩经历不同应力途径后岩石晶粒内的微破裂特征的观测进行了研究.实验中岩石样品首先承受较高的围压(使应力差达到岩石强度的80%),然后分别按 A,B,C 三种途径进行实验.三种途径已在另一文中作了叙述(见地震学报第2卷第3期237页).实验结束后,将岩石样品切开,制成标准薄片及光片.通过显微镜的观测发现,三种应力途径所引起的微破裂性质明显不同.在 B 型实验中,长石晶粒内的微裂纹表现得短小,其长度多数不超过长石晶粒短轴的长度.整个岩石样品内微裂纹的分布密集于较小的范围内.在 C型实验中,倾斜裂纹数量增多,长石晶粒中的裂纹比 A 和 B 实验更长和更多,出现一种星状的微裂纹.观测到的辉长岩的微观现象可能说明与岩石标本过密、超膨胀现象有关.

     

    Abstract: The mierocracks within crystal grains of Jinan gabbro have been observed in experiments along various stress paths. We load the rock sample to a certain high stress state, the differential stress reaching about 80% of the ultimate strength of the gabbro specimen. Then further stress is applied along various stress paths A, B and C. These paths have been described in a previous paper (Geng et al., 1979). After unloading, the rock samples are cut and polished or thin sections are made. It is observed that there exist obvious differences in microfractures between the three cases. In case B, most of the mierocracks in plagioclase are shortened whose lengths are less than the minor axis of the plagioclase grains. These cracks are concentrated in rather narrow regions. In case C, the number of inclined mierocracks increases, and the mierocracks in the plagioclase grains become much longer and much more in number than that in case A and B. There appear some star-like mierocracks. It is possible that the microscopic feature in gabbro are related to the super-dense and ultra-dilatant state of the rock samples.

     

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