Relative strengths and deformation mechanisms of amphibole-rich rocks in hot and cold subduction zones (Invited)

Slow slip and tremor (SST) in subduction zones comprise geodetically-detected plate boundary slip at rates exceeding background plate rates, in conjunction with bursts of microseismicity, and can release >90% of convergence-related stress down-dip of the megathrust. SST occurs over an incredible range of Pressure-Temperature conditions, so identifying specific characteristics of an SST-producing environment is challenging. One common denominator is the presence of metamorphosed oceanic crust containing amphibole as a strain-accommodating phase. However, the rheology of amphibole is poorly constrained, so its contribution to steady-state strength and/or slip transients is unknown. Here, we present observations of natural amphibole microstructures from exhumed subduction complexes that record hot and cold subduction geotherms and span a P-T range that encompasses observed SST in active margins, in order to constrain first-order effects of temperature on operative deformation mechanisms that may favor steady-state creep vs. creep transients. Depending on temperature, the presence/distribution of other phases, and fluid content, amphibole may be capable of accommodating steady-state flow and/or deformation transients over the range of observed SST depths.