We conducted experiments in which a granular mixture of quartz and labradorite was deformed in compression at elevated temperatures (200--350 ¿C) and pressures (100 MPa) in the presence of deionized water. Following initial consolidation of the material by application of the loads at room temperature, a second, hydrothermal phase of consolidation was observed when the temperature was increased with the loads fixed. The strain rate during this hydrothermal consolidation decayed approximately exponentially with time and was accompanied by only minor porosity reduction. The sample permeability decreased rapidly during the hydrothermal consolidation and continued to decrease following cessation of the deformation. The rate of this self-sealing process was a complex function of temperature. Scanning electron microscopy and microprobe analysis of the indurated post-experimental material showed albitization of the feldspar, especially in highly deformed regions. Analysis of post-experimental fluids show that Si in solution increased with increasing flow and temperature. Fluid-rock equilibrium was not achieved within the short durations of the experiments (50--60 hours). Our interpretation is that deformation occurred by grain boundary sliding aided by solution and reaction at high stress contacts, and sealing occurred by precipitation in low stress regions in the throats of pores. ¿ American Geophysical Union 1995