Ductile thrusting in the Himalayas: Shear sense criteria and stretching lineations

Abstract

The most useful criteria used for the determination of the sense of shear can be found in the huge Himalayan ductile shear zone known as M.C.T. They allow the determination of the sense of shear in relation with an unequivocal southward‐directed intracontinental thrust. The various criteria analyzed at different scales of observation show the permanence of the shear flow regime throughout the metamorphic evolution. However, most of the observed shear‐criteria are due to late nappe emplacement postdating the climax of the metamorphism. The most striking feature is the stretching lineation which is roughly normal to the thrust trace all along the belt. It parallels everywhere the shear direction and thus indicates the transport direction of the nappes. The observed radial pattern of stretch trajectories implies that the local motion does not correspond to the average plate convergence.