Strain trajectories above the Main Central Thrust (Himalaya) in southern Tibet

Abstract

As a result of the collision of India with Asia^1–3, a thick pile of Precambrian crystalline rocks (the Main Central Sheet) was transported southwards over the Indian continent. A marked linear fabric (a mineral-stretching lineation) within the Main Central Sheet varies only slightly from a north–south trend which is interpreted as paralleling the direction of transport of the nappe^3–6. Our study sought to extend the previous observations to the hitherto-poorly-known part of the Main Central Sheet in southern Tibet (China). The stretching lineation is dominantly north–south in the lower part of the sheet, but exhibits continuous and discontinuous variations from north–south to east–west in the upper part⁷. These variations of lineation trajectory indicate two shear components, one subparallel to, and one at a high angle with, the Himalayan belt. The recognition of westward wrench shearing in the Main Central Sheet implies a component of relative displacement parallel to the Himalayan belt and not only a radial one as generally assumed in previous models. This suggests that the kinematic story of the intracontinental deformation following the continental collision is probably not one of simple north–south convergence.