3-D Seismic Tomography and its Geodynamic Implications for Local and Regional Tectonics in the Northwest Himalayas
Abstract
3-D seismic tomography reveals variations in the crustal thickness and heterogeneous architecture of the crust and uppermost mantle beneath the Northwest Himalayas. Top low-velocity anomaly of the model down to depths of ~ 40 km in the Foreland to ~ 80 km depth below the Higher Himalayas represents crust. Lower limit of this anomaly represents variations of Moho depth. Estimated Vp and Vs tomograms are well consistent and in good agreement with overall geotectonic structures of the region. Estimated tomographic image is well corroborated with observed Bouguer gravity anomalies. Sediments or highly fractured/fault zones are imaged as low-velocity zones and rigid hard rocks as high-velocities. This low velocity anomaly is attributed to deeper roots/thicker crust containing sedimentary wedge and underthrusted crustal part of the Indian plate. The crustal thickness below the Himalayas varies both from south to the north in the direction of the Indo-Asia N-S convergence as well as along the tectonic trend of the Himalayas. Bottom high-velocity anomaly gently dipping northward beneath the Higher Himalayas and moderately dipping northwestward beneath the western Syntaxis. Thus represents underthrusting beneath the Himalayas parallel to Indo-Asia convergence and subduction towards northwest beneath the Hindu Kush, suggestive of an oblique convergence in this complicated region. A narrow bend in dipping high-velocity Indian mantle lithospheric slab observed just below the Kashmir Himalayas represents the buckling effect under the influence of horizontal stresses. This varied architecture and oblique convergence of the lithosphere are well corroborated with the focal mechanisms and GPS vectors. The along-strike varied architecture of the lithosphere represents the along-strike variation in the mechanical strength and the tectonic style that might be related to different stages in the temporal evolution of the Himalayas. We interpret that initial geometry, episodes of collision, acceleration/deceleration during collision, and rotations of Indian plate may lead to variation in the architecture of the lithosphere. The Delhi-Haridwar Ridge imaged as a high-velocity body behaves as a beam that rams into the Himalayas has a profound influence on the tectonics of the Himalayas, causing local buckling of the crust.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T21F0398R
- Keywords:
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- 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS;
- 8121 Dynamics: convection currents;
- and mantle plumes;
- TECTONOPHYSICS;
- 8170 Subduction zone processes;
- TECTONOPHYSICS;
- 8180 Tomography;
- TECTONOPHYSICS