11:30 AM - 11:45 AM

# [SSS15-15] Effects of dissolution−precipitation creep on the frictional properties of opal gouge at low-temperature hydrothermal conditions

Keywords:frictional properties, opal gouge, low-temperature hydrothermal conditions, dissolution−precipitation creep

*T*) ranging from room

*T*to 200°C, and at displacement rates (

*V*) changed stepwise among 0.1155, 1.155 and 11.55 μm/s. We then fitted the friction data for each step change in

*V*by the rate- and state-dependent friction constitutive law, and obtained the optimized (

*a*−

*b*) value, i.e., an indicator of frictional stability, at each

*V*.

The results show that steady-state friction coefficient μ

_{ss}increases with increasing

*T*, from 0.64 at room

*T*to 0.67 at 200°C, which is consistent with slip hardening behavior observed at higher

*T*s. Microstructural observations reveal that significant grain interlocking and porosity reduction occur in the gouge layer sheared at higher

*T*s. Thus increasing gouge lithification with increasing

*T*, which is promoted by thermally activated dissolution–precipitation creep, is likely responsible for increasing μ

_{ss}with increasing

*T*.

Our results also show that (

*a*−

*b*) value tends to decrease with increasing

*T*or decreasing

*V*at

*T*≧50°C. Decreasing (

*a*−

*b*) value with decreasing

*V*at a given

*T*is likely due to increasing gouge lithification and hence μ

_{ss}with decreasing

*V*, which is promoted by dissolution−precipitation creep favored at lower

*V*s. At a given

*V*,

*a*value does not change much while

*b*value increases with increasing

*T*, which results in decreasing (

*a*−

*b*) value with increasing

*T*. Increasing

*b*value with increasing

*T*implies that more strength recovery occurs when

*V*is stepped down, which is also ascribed to increasing activity of dissolution−precipitation creep. Because (

*a*−

*b*) value does not change with

*V*at room

*T*, dissolution−precipitation creep was not active at room

*T*.

At a given

*V*, the transition from

*a*−

*b*> 0 to

*a*−

*b*< 0 occurs with increasing

*T*, but the transition

*T*is also dependent on

*V*, because (

*a*−

*b*) value is dependent on both

*T*and

*V*as described above;

*T*<50°C at

*V*= 0.1155 μm/s, 50°C<

*T*<100°C at

*V*= 1.155 μm/s, and

*T*>100°C at

*V*= 11.55 μm/s. Our results suggest that increasing activity of dissolution−precipitation creep with increasing

*T*or decreasing

*V*promotes decreasing (

*a*−

*b*) value and hence the transition from stable aseismic faulting with

*a*−

*b*> 0 to unstable, possible seismic faulting with

*a*−

*b*< 0.