Crustal Thickness Variations and their Tectonic Implications beneath the
Uttarakhand Himalayas and the adjoining Tectonic Segments: Results from
3-D Tomographic Inversion of Local and Regional Earthquake Data
Abstract
We image the high-resolution velocity structures of the crust and
uppermost mantle beneath the western part of the Himalayan-Tibetan
orogen through tomographic inversion of local and regional earthquake
data. We herein reconstruct and present the tomographic image of the
variable configuration of the Moho boundary beneath the
Himalayan-Tibetan orogen. The thickness of the crust varies between
~40-65 km from south beneath the sub-Himalaya to north
beneath the Higher Himalaya. The thickest crust imaged as thick as
~85 km, located ~100 km from ITSZ
towards north beneath the southwest Tibet. Our results also report
significantly variable geometry of the Moho boundary along the tectonic
trend of the Himalayan-Tibetan orogen, which may indicate that the
Indian plate subducted/underthrusted beneath the Eurasian plate in a
piecewise manner as a consequence of differential convergence rates,
counter clockwise rotation of the Indian plate and episodic collision
processes. We also image the geometry of the subducting/underthrusting
Indian plate beneath the Himalayan-Tibetan orogen. We present the
geodynamic model of the two subducted slabs, where the Indian plate
subducts/underthrusts towards north and the Tibetan slab subducted
southwards beneath the Tibetan plateau. We infer that the Indian plate
is torn into pieces differing in its northern limits and angle of
subduction/underthrusting. Where its westernmost end
subducts/underthrusts below the Eurasian plate with a gentle dip
crossing ITSZ and KKMF. On the other hand, towards east the Indian plate
subducts/underthrust the Eurasian plate with a relatively greater angle
near ITSZ, approximately 250 km distant from HFT.