Influence of Deccan volcanism/synrift magmatism on the crust–mantle structure and its implications for the seismogenesis of earthquakes occurring in the Kachchh rift zone

Abstract

AbstractThe present study focuses on the delineation of the crust–mantle structure underlying the Kachchh rift zone (KRZ), by modelling P-wave receiver functions (P-RFs) and P-wave teleseismic tomography. Our RF study delineates marked crustal and lithospheric thinning below the central KRZ relative to the unrifted surrounding regions. This thinning model receives further support from crust-corrected normalized P-residuals, which suggest dominant negative residuals associated with the central KRZ. Teleseismic tomography using these P-residuals reveals low velocity to a depth of 170 km below the central KRZ, while there are positive residuals associated with the surrounding unrifted zones. Such a complex heterogeneous crust–mantle structure, which could be related to K/T boundary Deccan mantle plume activity and rift-related magmatism, might play a crucial role in seismogenesis of lower crustal earthquakes that have occurred in the KRZ since 2001. Inverted crust–mantle models obtained from P-RFs suggest a low shear velocity zone extending from 70–110 to 170–220 km depth beneath the central KRZ. This receives further support from the presence of low P-wave velocity down to 170 km modelled using teleseismic tomography. This low Vp and Vs zone in the upper mantle could be explained by the presence of trapped melts related to Deccan volcanism at 65 Ma or older rift-related magmatism.