热水条件下透辉石的摩擦本构特征

An experimental study of frictional constitutive properties of diopside under hydrothermal conditions

为了研究下地壳主要造岩矿物之一的辉石在摩擦滑动中的力学性质,本文选择辉石中的透辉石作为实验样品,在约200 MPa有效正应力(30 MPa孔隙水压)及100~600℃的热水条件下进行了速度阶跃摩擦滑动实验,在滑动开始后将剪切滑动速率在0.122μm·s^-1和1.22μm·s^-1之间进行切换来确定摩擦滑动对速度变化的响应.通过实验发现:透辉石在102~200℃表现为速度强化,随着温度升高,在约215℃附近从速度强化转变为速度弱化.在310℃以上,速度弱化的程度受温度的影响不大,而且摩擦本构参数a值和b值随温度的变化趋势相同.对变形样品的显微观测发现,与其速度强化行为相对应的微观变形主要以数条平行的R1剪切为主,卸样时造成的裂纹集中在R1剪切内部,形态长而曲折;与其速度弱化行为相对应的断层泥内部,剪切带变窄且数量明显增加,在内部互相连接,在边界附近多发育B剪切,卸样时形成的裂纹大量存在于B剪切带与R1剪切附近,形态短且平直.

To investigate the sliding properties of pyroxene as one of the main rock-forming minerals in the lower crust,we employed diopside(clinopyroxene)as a gouge sample to perform velocity-stepping sliding tests under hydrothermal conditions with an effective normal stress of about 200 MPa,pore pressure of 30 MPa and temperatures from 100℃to 600℃.During shearing,sliding rate was stepped between 0.122μm·s^-1 and 1.22μm·s^-1 to acquire the rate dependence.In the tests,diopside was found to be velocity-strengthening between 102℃and 200℃,which transitioned to velocity-weakening at about 215℃.Above 310℃,the degrees of velocity-weakening were not significantly affected by the increase of temperature,and the velocity dependence parameters a and b values exhibited similar temperature dependence.Microscopic observations on deformed samples showed that the main microstructural feature associated with the velocity-strengthening behavior was dominated by several through-going R1 shears,cracks with curvatures induced by unloading formed mostly along R1 shears.The main microstructural associated with the velocity-weakening behavior was featured by more distributive planar shears,B shear zones at gouge-wall rock boundaries were widely found,leading to much more short and straight cracks induced during unloading.