Modelling the lower crust by simulation of the in situ conditions: an example from the Saxonian Erzgebirge

Abstract

Seismic data supply an image of the Earth's interior with more detail than other geophysical methods. However, interpretation of the data is a complicated process. Laboratory investigations of rock properties under simulated in situ conditions can make a valuable contribution. For the material interpretation of the seismic profile DEKORP 3-MVE'90 along the Saxonian Erzgebirge in Germany, rock samples from this area were investigated under high-pressure-high-temperature conditions. The aim of the investigations was to find relations between longitudinal and shear-wave velocities, V p and V s, and the mineral composition of the rocks under extreme conditions of pressure and temperature. The experiments with different pressure chambers were made using two types of pressure apparatus: one allows numerous experiments at relatively low pressure; for measurements at extreme conditions up to 2 GPa and 1000°C, with partial melting, a special arrangement inside a gas pressure chamber was used. The experimental data are used for the construction of velocity vs. depth curves. Together with seismic velocity models and the geological interpretation of reflections these data allow the construction of a crustal model of the Erzgebirge. It can be shown that there are indications of partial melting zones in the lower crust. The results provide an example of the importance of this method for the material interpretation of seismic data in general.