Thermal and mechanical evolution of shear zones

Physical models of geological shear zones are computed taking into account heating by deformation and consequent softening of the rock. The models show that initiation of a ductile shear zone proceeds by the rapid build up of a thermal peak and by concentration of the strain. After this the temperature levels off as the widths of the thermal anomaly and of the sheared volume slowly increase. For imposed velocities compatible with plate motion, shear heating softens the rock efficiently but does not produce melting. This is not true in stratified structures where a sheared hard layer can heat up sufficiently to melt a neighbouring layer. Other situations where melting might occur are also analysed.