Seismic Imprints of Plume‐Lithosphere Interaction Beneath the Northwestern Deccan Volcanic Province

Abstract

The interaction of the Indian continental lithosphere with the Reunion plume resulted in massive outpouring of basalts manifested in the Deccan Volcanic Province. Although it is postulated that preexisting weak rift zones facilitated the eruption, deeper signatures of the plume remain contentious. In this study, we investigate the shear wave velocity (Vs) structure of the crust and upper mantle by inverting regionalized group velocity dispersion data in the period range of 6 to 100 s, down to 220 km depth, using the genetic algorithm technique. We used 1,286 dispersion curves derived from waveforms of 77 regional earthquakes recorded at 38 broadband stations. Our results reveal distinct intracrustal layers, Moho, mantle lid, and asthenospheric low‐velocity layer. Signatures of magmatic underplating are recognized in terms of high Vs and a thick crust beneath the Kutch seismic zone and Western Ghats. The lithospheric thickness varies from 80 to 124 km, being thinnest at the junction of Cambay and Narmada rifts, which could be the source zone of volcanic eruption. A thin lithosphere has also been observed beneath the Kutch seismic zone. A low‐velocity zone at depths ~80 km can be related with upwarping of the asthenosphere and/or presence of partial melts. A predominant low‐velocity zone beneath the Cambay, Saurashtra, and adjoining regions may be due to the effect of a residual thermal anomaly. A thin lithosphere beneath northwestern Deccan Volcanic Province could be the result of weakening due to plume‐lithosphere interaction, which facilitated volcanism through preexisting rift zones.

A review of seismological research in India during the past five years (2015-2019)

“…The tomography images clearly indicate the variation of Moho depths from ~30 to 45 km. Similar to the results from surface wave studies (Sharma et al, 2018), the tomography study also ascertains an increase in crustal thickness beneath the Kachchh rift zone (KRZ). Crustal thickening beneath the Kachchh region where the 2001 Bhuj earthquake occurred and most other regions associated with local seismicity and swarms suggests that crustal thickness is an important parameter that controls the lithospheric strength and locales of tectonic deformation.…”

“…The results enable constructing an apriori model for 3D inversion studies and improved hypocentral locations studies. A comprehensive understanding of the NWDVP region is attempted by inverting the regionalized group velocity dispersion data in the period range of 6 to 100 s, which reveals distinct intracrustal layers, Moho, mantle lid, and asthenospheric low velocity layer (Sharma et al, 2018). The signatures of magmatic underplating were deciphered from high Vs and a thick crust beneath the Kutch and Western Ghats.…”

Low‐Velocity Zones and Negative Radial Anisotropy Beneath the Plume Perturbed Northwestern Deccan Volcanic Province

“…Similar values are found beneath the Narmada (V SV 3.87 km/s; V SH 3.96 km/s) and Kutch (V SV 3.89 km/s; V SH 3.97 km/s) rift regions, except the KSZ (zone of high seismicity and magmatic perturbations; Rastogi et al., 2014; Pavan Kumar et al., 2017). In the KSZ (cell a6), high V SV (4.01 km/s) and V SH (4.09 km/s) values are estimated along with a thick crust, implying magmatic underplating (Sharma et al., 2018). Conversely, beneath the basalt covered Saurashtra, Central India, South Gujarat and Maharashtra regions, high V SV values of 3.85–3.98 km/s and V SH values of 3.94–4.09 km/s are estimated for the lower crust, with a crustal thickness of 35–39 km.…”

“…SV (4.01 km/s) and V SH (4.09 km/s) values are estimated along with a thick crust, implying magmatic underplating(Sharma et al, 2018). Conversely, beneath the basalt covered Saurashtra, Central India, South Gujarat and Maharashtra regions, high V SV values of 3.85-3.98 km/s and V SH values of 3.94-4.09 km/s are estimated for the lower crust, with a crustal thickness of 35-39 km.…”

“…Also, it is proposed that rifting along the Narmada graben was initiated during the late Cretaceous period, prior to the flood basalt volcanism, followed by its breakup from Seychelles that formed its western extension (Biswas, 1987). The hypothesis for the existence of a plume head at the junction between Narmada and Cambay rift systems gains support from the observation of a thin (∼80 km) lithosphere and an LVZ, inferred from modelling of Rayleigh wave dispersion data (Sharma et al, 2018). Also, based on teleseismic P-wave travel time tomography, Kennett and Widiyantoro (1999) document presence of a cylindrical LVZ between 80 and 250 km depth beneath the northwestern DVP and infer that the plume head is located in the north Cambay region.…”