THE ORIGIN OF S-C MYLONITES AND A NEW FAULT-ZONE MODEL

This paper presents a synthesis of experimental data on mechanical behaviour and deformation textures of simulated halite shear zones with special regard to the internal structures of S-C mylonites and their mechanical implications. Halite is the only mineral so far for which a complete transition between brittle shearing deformation to fully ductile shearing flow in the dislocation glide regime has been studied experimentally under large shear strains that may be encountered along faults or plate boundaries. Moreover, deformation textures in the shear zones are similar to those of mylonites and cataclasites. Thus the experimental results provide an insight into the petrogenesis of fault rocks, mylonites in particular, and the establishment of a realistic fault model. Existing fault models are critically examined from the viewpoint of the halite experiments, and a new fault model is proposed whereby fault zones are divided into brittle, semibrittle, semiductile and ductile regimes with increasing depth.