Passive seismological imaging of the Narmada paleo-rift, central India

• Shear wave structure of the Proterozoic Narmada rift.
• Thick crust within the rift with evidence for magmatic underplating.
• Evidence for anisotropy frozen in the mid and lower crust.
• Fast axis of anisotropy perpendicular to the rift.

The Narmada-Son lineament (NSL) is a prominent, nearly E–W trending tectonic feature dividing India into the peninsular and extra-peninsular regions. It marks the possible suture between two contrasting geological settings termed proto-continents lying to the North and South of it. Various views prevail about the nature of the rift zone. The present study delineates the seismic structure of the crust using P wave receiver functions at 10 broadband seismic stations installed along a profile across the NSL. The results from Common Conversion Point (CCP) stacking reveal a near continuous image of the Moho boundary, with the amplitudes of the Ps conversions from the Moho being weaker at stations within the rift. Modelling the receiver functions employing nearest neighborhood algorithm approach brings out a distinct (15 km) thickening of the crust and a complex nature of the Moho within the rifted zone. We find that the backazimuthal variations of the SV and SH receiver functions at the permanent station Jabalpur can be explained better by introducing azimuthal anisotropy in the middle and lower crust with the fast axes perpendicular to the rift axis. Also, we find substantial evidence of post rifting magmatic underplating in the lower crust, which could be reminiscence of Deccan volcanism and/or Reunion plume path.

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