Abstract

We derive a well‐resolved 1D model of shear‐wave velocity (VS) through both linear, and nonlinear joint inversions of Rayleigh‐ and Love‐wave group velocity dispersion data. Our best model from the deterministic approach suggests a two‐layered crust over a half‐space: the upper crust is 13.8 km thick with a shear velocity of 3.22  km/s; for the lower crust they are 24.9 km and 3.62  km/s, respectively. Finally, we use a global optimization method (very fast simulated annealing) to estimate shear‐wave velocity. Multiple models give acceptable fits to the observed data. A common feature of these models is a low‐velocity zone (LVZ) with its upper boundary at 60–70 km depth. At this depth, the temperature–depth profile of Kachchh cuts the wet peridotite geotherm, resulting in increased water content due to partial melting, and thus the decreased shear velocity. This LVZ extends down to a depth of 120–130 km, where the temperature–depth profile of Kachchh cuts the dry peridotite geotherm that leads to a sharp decrease in water content, thereby, a sharp increase in shear velocity. The maximum VS perturbation of −3% in the upper mantle can be explained by the presence of 100–150 K excess temperature beneath northwestern India at 70–120 km depth relative to the adjacent mantle along with the presence of 1% penny‐shaped melt inclusions (probably CO2‐rich carbonatite melts) in the upper mantle. This is likely related to the imprints of the initial Deccan/Reunion plume head that might have moved with India since the Deccan volcanism at 65 Ma.

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