Contrasting frictional Stability of Olivine and Quartz: Rotary ShearExperiments under Hydrothermal Conditions

In this study, we conducted rotary shear experiments to examine the frictional stability of Olivine and Quartz gouges over a range of temperatures (25–350 °C), slip velocities (100 μm s⁻¹ to 1 mm s⁻¹), and under a constant normal stress of 50 MPa. The two minerals exhibit contrasting stability behaviors: Olivine remains frictionally stable at room temperature but develops pronounced stick–slip instabilities at 350 °C. This unstable behavior persists at the velocity of 1 mm s⁻¹, although peak friction decreases slightly, indicating minor weakening. Quartz, by contrast, displays repeated stick–slip events at 25 °C, with stress drops that grow progressively larger with slip and are accompanied by continuous compaction, consistent with ongoing grain crushing. At 350 °C, Quartz behavior evolves from strong stick–slip at low velocities to stable sliding at higher velocities. These observations suggest that frictional stability is likely governed by a competition between the rate of tectonic loading, the specific healing kinetics, and the localization state of each mineral.