Alissa Kotowski is an Assistant Professor of Structural Geology and Electron Microscopy in the Department of Earth Sciences at Utrecht University in the Netherlands. She is originally from Boston, MA and earned her BSc from Boston College in 2014. She then earned her PhD from the University of Texas at Austin in 2019 where she was a National Science Foundation Graduate Research Fellow and worked on exhumed subduction zones to reconstruct structural and rheological evolution and interrogate the rock record to constrain mechanisms of slip transients in subduction zones. She then moved to Montreal, Canada where she was a Postdoctoral Research Fellow at McGill University. At McGill, she started to incorporate an experimental approach to her research, using nanoindentation to probe mineral plasticity, with a particular focus on amphiboles. Now as an Assistant Professor she is leading an active and lively research group that primarily focuses on the flow behavior of solid earth materials including ice and silicate rocks, but with emphasis on the initiation and maintenance of subduction plate boundaries both on the modern earth and deep in Earth’s history.

Strength and deformation mechanisms of amphibole-rich rocks in hot and cold subduction zones

Alissa J. Kotowski

Assistant Professor

Department of Earth Sciences

Utrecht University

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. I will compare natural amphibole microstructures from three exhumed subduction complexes that record hot, warm, and cold subduction geotherms, spanning a P-T range that encompasses observed SST in active margins, and discuss the deformation conditions and mechanisms that may produce transients. Using nanoindentation experiments, I will then provide new insight into low-temperature plasticity in glaucophane, to discuss the implications of dislocation-accommodated deformation in cold shear zones. 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.