In this study, we investigate the transition zone discontinuities beneath the northwestern Deccan volcanic province of India through analysis of ∼1000 high-quality receiver functions abstracted from three-component teleseismic waveforms from 428 earthquakes recorded by six broadband stations in the northwestern Deccan volcanic province. Our analysis reveals that the P410s and P660s time lags are delayed by ∼1 s relative to those predicted by the IASP91 model. A largely unperturbed mantle transition zone, revealed by the transition zone time lag (tP660s – tP410s) of 23.83 s, implies that the observed delays are primarily associated with reduced shear velocities in the upper mantle above the 410 km discontinuity. The velocity reduction is likely to be associated with lithospheric thinning coupled with compositional and reduced thermal variations in the shallow upper mantle. Our results contrast with the normal shield-like velocity structure imaged beneath the south-central Deccan volcanic province in an earlier receiver function study. For comparison, a revised composite receiver function plot for the south-central Deccan volcanic province was constructed by employing identical receiver function processing techniques on an updated high-quality data set of 1400 receiver functions from 11 stations, which reaffirms, with better precision, the earlier results. We propose that the relative differences in the lithospheric thicknesses beneath the northwestern and south-central parts of the Deccan volcanic province possibly governed the melting and flow patterns of the upwelling mantle material, resulting in the contrasting seismic signatures. The lithospheric architecture of the northwestern Deccan volcanic province, coupled with the reactivation of preexisting rift systems, appears to have facilitated the eruption of the Deccan basalts, for which source signatures are still retained in the upper mantle.
- Received 12 September 2011.
- Revision received 27 November 2011.
- Accepted 30 November 2011.
- © 2011 Geological Society of America