3‐D seismic tomography of the lithosphere and its geodynamic implications beneath the northeast India region

Abstract

We have evolved 3‐D seismic velocity structures in northeast India region and its adjoining areas to understand the geodynamic processes of Indian lithosphere that gently underthrusts under the Himalayas and steeply subducts below the Indo‐Burma Ranges. The region is tectonically buttressed between the Himalayan arc to the north and the Indo‐Burmese arc to the east. The tomographic image shows heterogeneous structure of lithosphere depicting different tectonic blocks. Though our results are limited to shallower depth (0–90 km), it matches well with the deeper continuation of lithospheric structure obtained in an earlier study. We observe low‐velocity structure all along the Eastern Himalayas down to ~70 km depth, which may be attributed to deeper roots/thicker crust developed by underthrusting of Indian plate. Parallel to this low‐velocity zone lies a high‐velocity zone in foredeep region, represents the Indian lithosphere. The underthrusting Indian lithosphere under the Himalayas as well as below the Indo‐Burma Ranges is well reflected as a high‐velocity dipping structure. The buckled up part of bending Indian plate in study region, the Shillong Plateau‐Mikir Hills tectonic block, is marked as a high‐velocity structure at shallower depth. The Eastern Himalayan Syntaxis, tectonic block where the two arcs meet, is identified as a high‐velocity structure. The Bengal Basin, tectonic block to the south of Shillong Plateau, shows low velocity due to its thicker sediments. Based on the tomographic image, a schematic model is presented to elucidate the structure and geodynamics of Indian lithosphere in study region.

Direct structural evidence of Indian continental subduction beneath Myanmar

“…1A), connects the ongoing India-Asia collision along the Himalayas in the north to the newly formed oceanic crust in the Andaman Sea in the south 9 . The seismicity outlines a Wadati-Benioff zone beneath Myanmar [10][11][12] that approximately coincides with a broad high-velocity structure revealed by regional and global tomographic studies, hinting at ongoing subduction 4,13,14 . However, given the lack of detailed geometry and structures, the nature of the ongoing subduction and the related tectonic regime remain unclear.…”

Active Convergence of the India‐Burma‐Sunda Plates Revealed by a New Continuous GPS Network

“…The presence of a subducted Indian slab imaged beneath the Burma plate implies that subduction of the Indian slab occurred sometime in the past and drove the convergence between the India and Burma plates (Bijwaard et al, ; Pesicek et al, ; Raoof et al, ). However, the absence of notable seismicity on the interface between the India and Burma plates has led some authors to speculate that subduction of the Indian slab has ceased or continues purely aseismically (le Dain et al, ; Ni et al, ).…”

Seismicity and structure of the Indian subcontin

“…The velocity structures at different scales of the Indian lithosphere are studied by several researchers employing different approaches such as seismic body wave tomography (Ramesh et al, 1990(Ramesh et al, , 1993Kennett and Widiyantoro 1999;Kayal and Mukhopadhyay, 2002;Mishra et al 2003;Mandal and Pujol, 2006;Mishra 2013;Singh et al, 2015;Koulakov et al, 2018Koulakov et al, , 2015Raoof et al, 2017;, surface wave tomography (Bhattacharya, 1981;Acton et al, 2010), receiver functions (RF) (Rai et al, 2003;Gupta et al, 2003;Kiselev et al, 2008;Ravi Kumar et al, 2013;Kumar et al, 2007Kumar et al, , 2013, joint inversion of body and surface wave analyses (Rai et al, 2003;Julia et al, 2009;Saikia et al, 2017), body wave propagation (Krishna et al, 1999;Krishna and Ramesh, 2000), and by magnetotellurics (Gupta et al, 1996;Naganjaneyulu and Santosh, 2012;Pavan Kumar et al, 2017), heat flow (Negi et al, 1986;Roy and Rao, 2000) and xenolith studies (Babu et al, 2009). Lithospheric structures in different tectonic domains are summarized below.…”

“…The lithospheric structure beneath Tibet and the Himalayas is investigated based on surface-wave studies (Brandon and Romanowicz, 1986;Curtis and Woodhouse, 1997;Rodgers and Schwartz, 1998;Rapine et al, 2003), high-frequency body wave propagation (Barazangi and Ni, 1982;McNamara et al, 1997), bodywave studies employing the P-and S-wave receiver functions Vinnik et al, 2007;Zhao et al, 2011;Singh and Kumar, 2009;Xu et al 2017;Hazarika et al 2012;Kumar et al, 2013;Caldwell et al, 2013;Gilligan et al, 2015), body wave travel-time tomography (Tilmann et al 2003;Koulakov et al, 2015;Raoof et al, 2017), integrated seismic data including receiver functions and mantle anisotropy (Oreshin et al, 2008), finite-frequency tomography using teleseismic data (Liang et al, 2016). Their results show undulated mantle structure along the Himalayas as well as striking difference in mantle structure between the northern and southern Tibet, higher velocity, presumably colder and stronger mantle beneath southern Tibet versus slower, presumably warmer and weaker mantle beneath northern Tibet.…”

“…The seismic tomographic images of NE India and its adjoining areas shows high velocity dipping structures related to the under thrusting Indian lithosphere under the Himalayas and below the Indo-Burma ranges, Shillong plateau, the eastern Himalaya syntaxis, and low velocity thick sediments below the Bengal basin (Bhattacharya et al, 2010;Raoof et al, 2017). Raoof et al (2017) reported that the subducting Indian lithosphere goes down to ~600 km below the Indo- Burma ranges. They also proposed that the lithosphere is buckled up below NE India and the crest of the buckled up part lies below Shillong plateau and Mikir Hills.…”