Plagioclase feldspar is a major mineral in mafic crustal rocks. To better understand the deformation mechanism of plagioclase feldspar during frictional faulting, we conducted shearing experiments on simulated plagioclase gouge in a wide range of effective normal stress of 100–300 MPa, pore-water pressure of 30–100 MPa, and temperatures ranging from 100°C to 600°C. The coefficient of friction is found to range from 0.65 to 0.74 across the entire temperature range, showing no significant thermal weakening process. Except for a case at 200°C with an effective normal stress of 300 MPa, the frictional sliding is velocity weakening over the whole temperature range, showing a steady-state rate dependence (a−b) ranging from −0.5 × 10⁻³ to −8.6 × 10⁻³. This property facilitates nucleation of unstable slips in frictional faulting. Above 200°C, the direct rate effect parameter (a) and the evolution effect parameter (b) of friction increase with temperature up to a threshold of 400°C or 500°C, depending on the effective normal stress. This thermal enhancement suggests thermally activated creep at contact junctions governed by intergranular pressure solution, as evidenced by microstructural signatures indicating the prevalence of very fine precipitates formed at the surfaces of gouge particles as a result of pressure solution. In frictional sliding of plagioclase, a low effective normal stress of 100 MPa corresponds to a higher degree of velocity weakening and tends to facilitate seismic slip rather than slow slips, whereas the high effective normal stress of 300 MPa corresponds to a minor velocity weakening which may cause slow-slip events in faults of limited size.

中文翻译：

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有效正应力100~300 MPa热液条件下斜长石凿岩失稳滑动及变形机制


斜长石是镁铁质地壳岩石中的主要矿物。为了更好地了解斜长石在摩擦断层过程中的变形机制，我们对模拟斜长石泥进行了有效正应力100~300 MPa、孔隙水压力30~100 MPa、温度100℃的剪切实验。 °C 至 600°C。在整个温度范围内，摩擦系数的范围为 0.65 至 0.74，表明没有明显的热弱化过程。除了 200°C 时有效法向应力为 300 MPa 的情况外，摩擦滑动在整个温度范围内速度减弱，表现出稳态速率依赖性 ( a−b )，范围从 -0.5 × 10 ^-3到−8.6 × 10 ⁻³ 。这一特性有利于摩擦断层中不稳定滑移的成核。在 200°C 以上，摩擦的直接速率效应参数 ( a ) 和演化效应参数 ( b ) 随着温度的增加而增加，最高可达 400°C 或 500°C 的阈值，具体取决于有效正应力。这种热增强表明接触接点处的热激活蠕变受晶间压力溶液控制，微观结构特征表明由于压力溶液在凿孔颗粒表面普遍形成非常细小的沉淀物。在斜长石的摩擦滑动中，100 MPa 的低有效法向应力对应于较高程度的速度减弱，并且倾向于促进地震滑动而不是慢速滑动，而 300 MPa 的高有效法向应力对应于较小的速度减弱，这可能会导致斜长石的摩擦滑动。在有限尺寸的断层中引起慢滑事件。