Crustal structure across the Deccan Volcanic Province and Eastern Dharwar craton in south Indian shield using receiver function modelling

Highlights

• Different crustal thickness and composition beneath the DVP and EDC

• Underplated layer below the DVP crust

• DVP is highly affected by the Reunion mantle plume-crust interaction.

• EDC is un-affected by any major tectono-thermal event for long geological time.

Abstract

The south Indian shield, primarily consisting of Archean cratons and Cretaceous-Tertiary Deccan Volcanic Province (DVP), has undergone several major tectonic episodes during its evolution. The Deccan volcanism at Cretaceous-Tertiary (~65 Ma) is the last major tectono-thermal event, which influenced a substantial part of the south Indian shield. To understand the influence of the Deccan volcanism on the evolution of the south Indian shield, we study the crustal seismic structure of the ~65 Ma Deccan Volcanic Province and the adjacent ~2.6 Ga Eastern Dharwar Craton (EDC), which forms the basement of the volcanic terrain. We calculate teleseismic receiver functions for 18 broadband seismic stations along a ~1000 km long seismological profile that cut across both the EDC and DVP. The analysis and modelling, using H-Vp/Vs stacking and generalized neighbourhood algorithm inversion of the receiver functions show distinct crustal structure (crustal thickness, average composition, shear wave velocity variation, nature of crust-mantle boundary, etc.) across the EDC and DVP. The results clearly indicate that the crustal structure is heterogeneous beneath the DVP compared to a relatively uniform structure below the EDC. Using results from this study along with earlier results, we infer that the present Eastern Dharwar Craton terrain is not affected by any tectono-thermal event for a long geological time, including the Deccan volcanism. Whereas, the present Deccan Volcanic Province is highly affected by the Reunion mantle plume-crust interaction.

Introduction

The south Indian shield consists of the Archean Dharwar craton, Archean-Proterozoic Southern Granulite Terrain (SGT) and Cretaceous-Tertiary (~65 Ma) Deccan volcanic Provinces (DVP). To understand the evolution of the south Indian shield, the knowledge of evolution of its different constituents is important and essential. While evolution of the Dharwar craton and Southern Granulite Terrain are quite well understood (e.g., Naqvi, 2005 and references within), the evolution of the Deccan Volcanic Province is a matter of debate between various theories proposed for the Deccan magma formation viz., by melting of a massive mantle plume, normal plate tectonic processes, or impact of a large extra-terrestrial bolide (e.g., Subba Rao and Sukheswala, 1981; Pandey and Negi, 1987; Duncan and Pyle, 1988; Mahoney, 1988; Sheth, 2005; Sen and Chandrasekharam, 2011).

The seismic methods, which provide detailed information on the seismic crustal structure (crustal thickness, composition, presence or absence of the basal cumulate layer in the lowermost crust, thickness of the basal layer, etc.) and upper mantle structure, also give insightful clues for the nature of the evolution of different tectonic terrains, when integrated with other geological and geophysical information. Various earlier seismic and seismological studies in the EDC suggest the presence of a simple, uniform crustal structure with Moho depth at ~35 km. The EDC crust is basically of felsic-intermediate composition with the absence of the basal layer (Kaila et al., 1979; Kumar et al., 2001; Rai et al., 2003; Gupta and Rai, 2005; Julia et al., 2009; Borah et al., 2014). However, the seismic and seismological studies, mostly in the western-most or NW part of the DVP suggest varying seismic crustal structure in terms of Moho depth, composition and presence or absence of the basal layer within the DVP (Krishna et al., 1991; Mohan and Kumar, 2004; Julia et al., 2009; Kumar and Mohan, 2014; Deshpande and Mohan, 2016). Moreover, based on the seismological investigations at randomly distributed seismic stations in the EDC and DVP there are differences in the opinion about the DVP crust, whether the DVP has altered crust due to the Deccan volcanism or the DVP crust is akin to the simple and uniform EDC crust (Das et al., 2015; Kumar and Mohan, 2014). Therefore, to understand the effect of the Deccan volcanism on the evolution of the south Indian shield, we study the crustal seismic structure of the DVP with reference to the crustal structure of the EDC through analysis and modelling of the teleseismic receiver function along a ~1000 km seismological profile across the EDC and DVP [Fig. 1a].