Permeability evolution of pseudotachylytes during hydrothermal alteration experiments

The apparently low abundance of pseudotachylytes in field outcrops of fault zones may be due to their alteration and hence destruction of characteristic microstructures. The potential for alteration of rocks is largely controlled by the availability of water that in turn depends on the rocks’ permeability. The permeability of pseudotachylytes, which generally exhibit a fine-grained matrix, is expected to be low relative to their host rock, such that infiltration by fluids should be minimal. We are therefore conducting flow-through experiments at elevated temperatures on pseudotachylyte samples from the Gole Larghe fault zone, Italian Southern Alps. We are monitoring the permeability and its evolution with time due to hydrothermal alteration processes using the pore-pressure oscillation technique. Microstructural analyses of naturally and experimentally altered pseudotachylytes will help to constrain the alteration processes and associated kinetics. Our results contribute to answer the question how pseudotachylytes are lost from the rock record.