Effect of fluid H2O on compressional wave velocities in quartz aggregate up to 500°C at 0.5 GPa

Compressional wave velocities (Vp) in quartz aggregate were measured to quantify the effect of pore fluid (H2O) on Vp at high pressure-temperature (P-T). Ultrasonic measurements were conducted on dry and wet quartz aggregate from room temperature to 500°C at 0.5 GPa using a piston cylinder apparatus. The experiment showed a 4% decrease in measured Vp in quartz aggregate with increasing H2O content to 1 wt.%, whereas the temperature derivative of Vp (∂Vp/∂T = −2.8 to −4.9 × 10 km s°C) in wet quartz aggregate remained almost the same as for the dry quartz aggregate (∂Vp/∂T = −5.2 × 10 km s°C). Our high-pressure, high-temperature experiments show that a small amount of pore fluid (0.4 to 1.0 wt.% H2O) can significantly reduce Vp under the P-T conditions of the middle crust.