A New Generation Griggs Apparatus With Active Acoustic Monitoring

High pressure and temperature experiments are necessary to understand geological processes at deep earth conditions. Here, we present a new generation Griggs-type apparatus, designed to perform deformation experiments at P-T conditions of the lower crust and upper mantle, i.e. up to 5 GPa and 1000 degrees C. We first detail the experimental design, set-up and procedure, as well as the calibration protocol of the apparatus. The main innovation of this new set-up is the development of an active acoustic monitoring pulse-transmission technique, which enables us to monitor the evolution of P-wave elastic velocities, at 5 MHz, contemporaneously with deformation. This may provide information on the evolution of the microstructure, in particular when mineralogical (metamorphic) reactions are taking place. For instance, P-wave velocity variations across the alpha -> beta quartz transition are recorded for the first time within a Griggs apparatus, at 0.5 and 0.8 GPa. This new set-up opens up important perspectives for the study of the complex couplings that may take place between mineral reactions and deformation under in lithospheric stress and temperature conditions.