Deformation microstructures of rocks and the rheology of lithosphere

本研究项目的主要任务是通过引进透射电子显微镜和调整最近安装在东京大学地震研究所的岩石形变仪器，建立一个研究岩石圈变形微结构和流变学的综合研究实验室。透射电子显微镜和离子稀释机将有助于研究构成断层中央部分的超细断层岩。本研究的主要成果如下：(1)根据断层的高速摩擦特性，提出了地震孕育的两相失稳模型，该模型可以解释第二类地震的平静。对天然断层岩的研究揭示了断层高速运动的证据。(2)研究了岩盐…在极端剪切作用下从脆性变形到中间变形再到全塑性变形的完全转变。利用高温双轴机，随着断层(如地温梯度)法向应力的增加，更多的剪切带在温度线性上升。这些实验首次揭示了岩石圈的强度剖面、糜棱岩变形的条件和孕震带下界的流变学意义。否定了以往的断层模型，提出了一种新的断层与板块边界模型。实验结果还表明，断层的流变性质受控于含量低至5%的弱组分矿物，表明层状硅酸盐在断层流变学中的重要意义。(3)提出了溶液-沉淀蠕变理论，并测定了溶质在岩石孔隙水中的扩散系数。这些结果成功地评价了压力溶液对岩石变形的影响。总结了高温条件下岩石摩擦性能的各种实验数据。(4)天然糜棱岩中位错密度与晶粒度的关系不同于实验变形岩石，表明变形完成后糜棱岩的变形微观结构发生了变化。低温糜棱岩的电子显微镜观察揭示了斜长石的动态重结晶。较少

The main task of the present research project has been to establish a comprehensive research laboratory for studying defomation microstructures and the rheology of the lithosphere by introducing a transmission electron microscopy (TEM) and by adjusting rock deformation apparatuses recently installed to Earthquake Research Institute, University of Tokyo. The TEM and an ion-thinning machine will be useful for studying the ultrafine fault rocks constituting the central part of faults. The major results from the present three-year project are as follows.(1) Two-phase instability model for the earthquake generation has been proposed based on the results of high-velocity frictional properties of faults, and the model may account for the seismic quiescence of the second kind. Studies of natural fault rocks have revealed evidence of high velocity fault motion.(2) Complete transition from brittle, through intermediate, to fully plastic deformation under extreme shear has been studied for halite … More shear zones at temperatures increasing linearly with an increase in the normal stress to the fault (as in the case of geothermal gradient) using a high-temperature biaxial machine. These experiments have revealed for the first time the strength profile of lithosphere, conditions for mylonitic deformation, and the rheological meaning of the lower bound of the seismogenic zone. Previous fault models were denied and a new fault and plate-boundary model was proposed. Experimental results also revealed that rheological properties of a fault is controlled by weaker constituent minerals whose content is as small as 5%, implying the significance of phylosilicates in the fault rheology.(3) A theory of solution-precipitation creep was proposed, and the diffusivity of solutes in pore water in rocks was measured. These results have successfully evaluated the effect of pressure solution on rock deformation. Diverse experimental data on the frictional properties of rocks under hydorthermal conditions have been summarized.(4) The relatioship between the dislocation density and the grain size in natural mylonites is different from that for experimentally deformed rocks, suggesting that deformation microstructures of mylonites have been altered after the completion of deformation. TEM observations of low-temperature mylonites revealed dynamic recrystallization of plagioclase. Less