Provenance of North Indian geoid ridge and its implication to collision evolution between India and Eurasia

Abstract

The geoid minima in the Indian Ocean and Siberia are separated by the North Indian Geoid Ridge (NIGR), yet the origin of the NIGR remains inadequately understood. Spherical harmonic analysis and geoid kernels indicate that the NIGR has wavelengths of degrees 7–10 and is mainly driven by density anomalies of similar degrees within the mantle. By employing numerical geoid modelling with four different tomography-derived density structures, we determined that abundant high-density anomalies in the mantle transition zone beneath North India and the Himalayas are responsible for the NIGR. Additionally, two contrasting tectonic evolutions of the India-Tibet collision, namely subduction roll-back scenario through the collision vs. lithospheric dripping scenario through the collision, are evaluated through geoid calculation. The former scenario suggests abundant high-density structures in the transition zone, capable of generating a well-constrained NIGR, while the latter does not support this. Consequently, we consider the Indian lithosphere subduction roll-back to be the more plausible evolving scenario.