Data from: Friction and instability of glaucophane gouges at blueschist temperatures support abundance of intermediate-depth earthquakes

<p>Fluid release from the hydraulically-confined dehydration of blueschist minerals may significantly elevate fluid pressures and concomitantly reduce effective stresses. This is a viable mechanism to explain brittle failure and frictional instability, and it is a possible explanation for intermediate-depth earthquakes in cold subduction zones. We examine this hypothesis for glaucophane – a key index mineral for blueschist facies – at lower confining stresses where behavior is poorly understood. We conduct laboratory shear tests on glaucophane gouge at temperatures of 100–500<em>℃</em> and effective normal stresses of 50–200 <em>MPa</em>, to explore the controls of temperature, stresses and excess pore fluid pressures on fault friction. Frictional strength of glaucophane gouge at representative temperatures and stresses is ~0.70 and insensitive to temperature with a slight increase in friction coefficient at lower effective stresses. Elevating temperature promotes a transition from velocity-strengthening to mild velocity-weakening behavior, indicating the destabilizing effect of high-temperature downdip in subduction zones. Reducing effective normal stress or concomitantly elevating pore fluid pressure, potentially sourced from dehydration reactions, further strengthens the velocity-weakening response and would be manifest as moderate-sized earthquakes. This observed instability at higher temperatures or lower stresses is indexed with and accompanied by denser distributions of strongly- to moderately-localized shears in the microstructures – congruent with the observed mechanical response. Our results support the potential for enhanced unstable sliding of glaucophane gouges at lower effective stresses and at blueschist facies temperatures - and have significant implications for understanding the abundance of intermediate-depth earthquakes apparent in cold subduction zones.</p>