In situ deformation of micas: A high-voltage electron-microscope study
In situ deformation of micas: A high-voltage electron-microscope study
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云母的原位变形：高压电子显微镜研究
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2007
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ANNnnrlnrr Mrrrn
在1500-kV透射电镜下室温原位剪切白云母（2M,）和黑云母（lM）。由此产生的位错活化是在造岩矿物中首次成功进行这类实验。在这两种云母中，只有基底滑移被激活，但位错可以从微观力学的角度来区分，这可能与延展性的宏观差异有关。尽管黑云母标本中沉淀较多，但白云母标本中的位错始终难以激活。白云母基底位错长且大致呈线性，沿[100]或[10]方向排列。他们以平行于脱位线的短步骤激活，这是典型的螺钉脱位方式。黑云母基底位错呈曲线状，并垂直于位错线呈弓形段推进，具有边缘位错的特征。位错线的分裂，通常被反向对比区或莫尔条纹区分开，被解释为位错解离。在黑云母中，解离作用似乎有助于绕过障碍物。提出的微力学差异的解释是基于佩尔斯势能在基滑面上的分布和其他能量最小化的论点。模型与观测结果的一致表明，微观力学差异在结构上是由八面体层决定的。根据微观力学差异的大小与温度之间的反比关系，可以从自然证据中评估提出的Peierls应力对位错活动的控制。
Muscovite (2M,) and biotite (lM)were sheared in situ at room temperature in a 1500-kV transmission electron microscope. The resultant activation of dislocations represents the first success of such an experiment in a rock-forming mineral. Only basal slip was activated in either mica, but the dislocations could be distinguished on micromechanical grounds that may be related to a macroscopic difference in ductility. Invariably, dislocations in the muscovite specimens activated with greater difrculty, despite the greater abundance of precipitates in the biotite specimens. Muscovite basal dislocations were long and roughly linear, oriented along [100] or I l0]. They activated in short steps that advanced parallel to the dislocation line, a manner typical ofscrew dislocations. In contrast, biotite basal dislocations were curvilinear and advanced perpendicular to the dislocation line in bowed segments, characteristic of edge dislocations. The division of dislocation lines, often separated by areas of either reversed contrast or moir6 fringes, was interpreted as dislocation dissociation. Dissociation appeared to facilitate obstacle circumvention in biotite. The proposed explanation for the micromechanical differences is based on the distribution of Peierls potential energy in the basal glide plane and other energy-minimization arguments. The agreement between the proposed model and observation suggests that the micromechanical difference is structurally determined by the octahedral layer. The proposed Peierls stress control of dislocation activity could be evaluated from natural evidence, based on an expected inverse relationship between the magnitude of the micro-mechanical differences and temoerature.