2000 Volume 109 Issue 1 Pages 56-72
The Himalayas are composed of E-W stretching mountain ranges formed as a foreland fold-thrust wedge. This paper discusses the latest phase of fold-thrust wedge development through morphogenesis and active tectonics of the Himalayan Front. The deformation front of the Himalayas is generally known as the sub-Himalaya or the Outer Himalaya. The sub-Himalayan morphostructure is characterised by a sequence of range-front anticlinoriums, which are fault-propagation-folds of the Himalaya Frontal Fault (HFF), and piggyback basins. Piggyback-basin deposition has been shifting from the Garhwal Front in Middle Pleistocene time to the Eastern Nepal Front in the Holocene. In other words, the morphogenesis of the HFF propagates from west to east. The lateral propagation of thrusting is considered to be possible under a left-oblique convergence between the Indian subcontinent and the Himalayas. The growth rate of the range-front anticlinorium is in accord with uplifting rate surveyed in interseismic periods. Conversely, coseismic deformation, which was recorded in the 1905 Kangra earthquake, was in conflict with the morphostructural profile of the sub-Himalaya. These facts suggest that interseismic slips chiefly generate the morphostructure of the Himalayan Front.