Elastic wave velocities of granite at experimental simulated partial melting conditions

Abstract

Laboratory investigations of ultrasonic wave velocities in granite samples from the Saxonian Erzgebirge were carried out under simulated in situ conditions. Using a gas pressure vessel with internal heating a method was developed to measure elastic wave velocities vp and v2 up to 1,000°C. In the case of a sample from the Kirchberg massiv (Erzgebirge) the velocity decrease with increasing temperature becomes extreme nonlinear at temperatures higher than 700°C. The influence on shear wave velocity is larger than on compressional wave velocity. Thermal cracking as a result of differential thermal expansion of the constituent minerals, the α-β transition of quartz and melting are discussed as possible reasons for this phenomenon. Thin sections of the sample after being subjected to temperatures of 750°C and 800°C and a pressure of 500 MPa show melt margins at grain boundaries. This fact and the temperature dependence of Poisson's ratio at 500 MPa support the conclusion that the velocity drop at temperatures above 700°C is mainly caused by partial melting.