热水条件下花岗质糜棱岩的摩擦滑动实验研究

为了探讨大陆地壳断层深部的力学性质，我们选择了采自红河断裂带的糜棱岩作为实验样品，进行热水条件下的高温高压摩擦滑动实验.实验在一个以气体为介质的高温高压三轴实验系统中进行.实验条件是：有效正应力为200 MPa；孔隙水压为30 MPa（在400 ℃到600 ℃之间为超临界水条件）；温度为100 ℃到600 ℃；轴向加载的速率范围从0.04 μm/s到0.2 μm/s再到1 μm/s.实验结果表明：（1）当温度小于300 ℃时，糜棱岩的摩擦强度随着温度的上升而增大；当温度大于300 ℃时，糜棱岩的摩擦强度随着温度的上升而减小.这种趋势和以往花岗岩的摩擦滑动数据基本一致；（2）糜棱岩在200 ℃和400 ℃时表现为速度弱化，其余温度下为速度强化；（3）糜棱岩与已有花岗岩的摩擦滑动数据并不完全一致；（4）花岗质糜棱岩速度弱化向速度强化转变的温度在430 ℃附近，以此我们可以推测：在变形机制为摩擦滑动的深部条件下，地震成核的深度范围可以比以往的估计更深.

An experimental study of frictional sliding of granitic mylonite under hydrothermal conditions

To investigate the mechanical properties of the deep portion of fault zones, we chose a mylonite sample collected from the Red River fault zone to conduct experiments of frictional sliding under hydrothermal conditions. Experiments were performed in a triaxial testing system with argon gas as confining medium with effective normal stress of 200 MPa, pore pressure of 30 MPa and temperature varied from 100 to 600 ℃. For temperatures over 400 ℃, pore pressure of 30 MPa corresponds to supercritical water conditions. During the experiments, axial loading rate steps were applied to obtain the rate dependence of friction in the velocity range from 0.04 μm/s to 1 μm/s. The following conclusions are drawn from the experimental results. (1) The strength of mylonite increases with the increase of temperature below 300 ℃ but decreases with temperature increase at higher temperatures. This trend is basically consistent with the results of granite in the literature. (2) The velocity dependence of mylonite shows velocity weakening at 200 ℃ and 400 ℃, but velocity strengthening occurred at other temperatures. (3) The frictional sliding behaviour of mylonite is not completely identical with previous data of granite. (4) The transition from velocity weakening to velocity strengthening for granitic mylonite occurs at about 430 ℃. According to this result, the depth of earthquake nucleation can be deeper than the previous estimate if frictional sliding is possible around the transition depth.