Semi-Brittle Deformation of Talc at the Base of the Seismogenic Zone

Talc is commonly found in the cores of exhumed faults and may be important to the dynamics of slip in active fault zones. To understand the rheology of talc at conditions relevant to subduction zones, we conducted torsional deformation experiments at high pressure (1 GPa) and temperatures (450–500°C). Scanning Transmission Electron Microscope imaging revealed a marked decrease in grain size with increasing strain, in addition to the development of grain kinking and nanoporosity. The similarity of these microstructures to talc deformed in natural faults and low-pressure experiments indicates that the dominant deformation mechanisms of talc are similar across a wide range of depths. We conclude that frictional processes remain an important control on talc rheology even under high normal stresses. However, deformation-induced porosity could enhance the percolation of high-pressure or reactive fluids through talc-rich lithologies.