| dc.description.abstract | Olivine (and enstatite) have been regarded as evidence of paleo-earthquakes within serpentinite shear zones. To investigate the serpentinite dehydroxylation and its influences on the fault strength in shallow subduction zone earthquake-like environments, we performed rotary-shear friction experiments on water-saturated serpentinite powders at a seismic slip rate at 10 MPa normal stress, either in fluid-drained or undrained conditions. Gouge temperature (T) was measured by a thermocouple ~1.5 mm from the slipping surface. Results showed that, in undrained experiments, the apparent friction coefficient dropped from a peak value of ~0.32-0.33 to a steady-state value of ~0.09-0.12, accompanied by gouge compaction and reached a max. T of ~180°C at the thermocouple by the end of the experiment. Drained experiments also displayed a drop from a plateau-like peak value of ~0.37-0.42 to a steady-state value of ~0.19-0.32, associated with gouge dilation and an increase of temperature from ~300°C to ~450°C. The friction coefficient then restrengthened to a value of ~0.29-0.55 with gouge compaction, and recorded a max. T of ~635°C at the thermocouple by the end of the experiment. Integrate microanalytical results from the polarizing microscope, thermal-emission field scanning electron microscope, focused ion beam-transmission electron microscope, and synchrotron X-ray diffraction showed frictional melts and serpentine dehydroxylated products only formed in the principal slip zone (PSZ) of drained experiments. As a result, we suggest that for undrained conditions, thermal pressurization of the pore fluid would lead to frictional weakening and buffered the temperature rise to below that required for serpentine dehydroxylation. However, in drained conditions, with increasing temperature, dehydroxylation of serpentine would first cause mechanical-thermal-chemical pressurization of pore fluid and lead to frictional weakening. As water moves out of the PSZ, frictional recovery would happen by the formation of viscous melts. We conclude that frictional melts (mixed with olivine and enstatite) generated behind rupture fronts, could not only likely become frictional barriers for the ongoing seismic slips but also be preserved as paleoseismic indicators, helping the recognition of paleoseismic events. | en_US |