Structures in the Tethys Himalayas and their Tectonic Significance

Structural studies of Tethys sediments between Malari and Lapthal show development of many minor structures e.g. - 'cleavages, tension and shear fractures' - which have been utilised to deduce the stress fields responsible for the deformation of these rocks. The primary sedimentary structures such as bedding, current bedding suggest shallow deposition conditions. The shape of folds, the fracture cleavages, quartz and calcite filled tension gashes and other fractures, and the thrusts are all taken as evidence for 'shallow-level' deformation of these rocks in which 'brittle deformation' was dominant.

The study suggests that major compressive stress responsible for the deformation of these rocks was always directed northeast-southwest and was lying sub-parallel to the earth's surface, the P-intermediate was directed NW-SE and was also horizontal, while the P-minimum was always invariably perpendic:ular to the earth's surface. Hence, it is concluded that these rocks have been deformed by horizontal compression and it appears that the major push was from the SW in this part of the ranges.