Creep Rheology of Antigorite: Experiments at Subduction Zone Conditions

Novel fluid medium pressure cells were used to deform antigorite under constant stress creep conditions at low temperature, low strain rate (10−9 − 10−4 1/s), and high pressure (1 GPa) in a Griggs‐type apparatus. Antigorite cores were deformed at constant temperatures between 75°C and 550°C, by applying 8–12 stress‐strain steps per temperature. The microstructures of deformed samples share features documented in previous work (e.g., shear microcracks), and highlight the importance of basal shear and kinks to antigorite plasticity. Rheological data were fit with a low temperature plasticity law, consistent with a deformation mechanism involving large lattice resistance. When applied at geologic stresses and strain rates, the extrapolated viscosity agrees well with predictions based on subduction zone thermal models. Plain Language Summary The rheology of Antigorite, a hydrous mineral that is present on top of subducting slabs and in the stagnant mantle wedge, could control subduction structure. Instead of deforming antigorite with our motor set to a constant speed, we redesigned the deformation assembly and machine to accurately servo‐control the stress on deforming samples. Measuring strain rate at several stresses and temperatures allows us to construct a flow law to extrapolate behavior to subduction zone stresses/strain rates. The microstructure of samples cut open after deformation suggests antigorite rheology is controlled by the resistance of defects to movement along the crystallographic sheet structure. Key Points Isotropic antigorite was deformed at constant stress to low strain Slip along basal planes and kinks allow plastic deformation A low temperature plasticity (LTP) creep law describes deformation rheology well