Seismic signatures of an altered crust and a normal transition zone structure beneath the Godavari rift

Abstract

The Godavari rift valley in the south Indian shield, located over a paleosuture between the Dharwar and Singhbhum cratons is a very less studied region in terms of its deep seismic structure. In the present study a total of 1559 receiver functions from 777 earthquakes registered by a 10 station network are utilized to investigate crust and mantle structure. Broadly, the crustal architecture underneath the rift appears very complex with the presence of intracrustal layers and a weak Moho compared to a sharp Moho and a simple crust outside it. Detailed modelling of receiver functions at 6 stations using the Nearest Neighbourhood Algorithm approach reveals a 40km thick crust within the rift compared to a 33km thick crust in the adjacent Dharwar craton. Also, the lower crustal character is found to be distinctly different, with a faster lower crust beneath the rift. A weak Moho beneath the rift may be due to magmatic underplating. The transition zone (660–410km) structure inferred from the common conversion point stacks of receiver functions can be interpreted in terms of the absence of (a) thermal anomalies within and above the mantle transition zone (MTZ) (b) thin lithosphere or high temperatures in the uppermost mantle. Magmatic underplating within the crust and a normal MTZ argue in favour of a rift formed due to lithospheric stretching without the influence of a mantle plume.