On the tectonics of the Western Himalaya

Abstract

The present study aims at making a contribution to the tectonics of the Western Himalayan Regions of Jammu, Kashmir and Ladakh. During the summer of 1978, the orientation of many joints has been measured in outcrops along the road from Jammuvia Srinagar to Leh. Based upon the contention that the visible rock-joints are shear surfaces produced by the neotectonic stress field, the principal stress directions of the latter can be calculated from a statistical analysis of the orientations of the joints. Furthermore, it has also been proposed that many valley trends follow tectonic shear zones. Thus, a statistical evaluation of the valley trends in Jammu and Kashmir has been made. The analysis of the orientations of joints and river valley trends has shown that, in both these features, there are two pairs of conjugate systems of directions. The first, the preponderant one, has preferred pole directions of N 55°E and N 138°E; it is produced by a principal horizontal compression with an azimuth of N 7°E. The second system is only vestigially developed in the joints, it has preferred pole-azimuths around N 92°E and N 358°E. Field evidence shows joints belonging to this second system to terminate at joints belonging to the first (preponderant) system which permits one to infer that the second system is older than the first and, thus, belongs to previous orientation of the tectonic stress field. In the valleys, both systems are almost equally well developed which indicates that earlier orientations are preserved in valleys for a longer time than in joints. The orientations of the neotectonic stress field deduced from joint-orientation measurements are in good conformity with the ideas of plate tectonics. Thus, India “pushes” (or is dragged) northward; the joints are slip surfaces fitting into this pattern.