Arc parallel extension in Higher and Lesser Himalayas, evidence from western Arunachal Himalaya, India

The existence of E–W extensional features from northeast (NE) Himalaya is poorly documented. Our investigation in the western part of Arunachal Himalaya provides evidences of active Quaternary E–W arc-parallel extensional features in the Higher and Lesser Himalayas. They are represented by arc-perpendicular normal faults and arc-parallel sinistral strike-slip faults. We discuss the occurrences of these arc-parallel extensional features in terms of oblique convergence and radial expansion models. The partitioning of stress due to oblique convergence is argued based on evidences of left-lateral slip in NE-Himalaya, right-lateral slip in NW-Himalaya and absence of translation in the central part. The amount of arc-parallel extension in the hinterland regions is correlated to the amount of radial shortening in the foreland. The computation of arc-parallel extension in the NE Himalayan arc is carried out by defining a small-circle centered at 88°39′±0.7′E longitude and 33°40′±0.6′N latitude having a radius of 770.7 ± 15.1 km, for the segment between 92°01′ and 95°16′E longitudes. The amount of arc-parallel extension estimated is ~110 km for the NE Himalayan segment. Our result agrees closely with the 104 km extension determined based on geodetically computed extension rate and age of initiation of rifting in southern Tibet.