Lithospheric architecture below the Eastern Ghats Mobile Belt and adjoining Archean cratons: Imprints of India-Antarctica collision tectonics

Abstract

The investigation of the rigid lithospheric mantle architecture floating over the weaker hotter asthenosphere is key to understanding the plate tectonic evolution of the Eastern Ghats Mobile Belt and the adjoining Archean cratons. We present shear-wave velocity (VS) structure for the crust and upper-mantle below the Eastern Ghats Mobile Belt (EGMB) and adjacent Archean cratons. The lithospheric structure is constrained through 4–150 s fundamental-mode Rayleigh and Love-wave group velocity dispersion measurements, using regional (2°–30°) earthquakes recorded at 27 seismic stations installed along two distinct profiles. Velocity models are improved by joint inversion of resultant dispersion curves with receiver functions computed from the teleseismic P-waves. Observed variations in crustal and lithospheric architecture across the domains of the Eastern Ghats Province are implication of the deformations due to rifting and collision of India and East Antarctica in the context of assembly and breakup of Rodinia and Gondwana supercontinents. The cratons and the mobile belt are characterised by 34–38 km, ∼45 km thick heterogeneous crust and 120–160 km, 90–120 km thick lithospheres, respectively. The abrupt changes in the crustal thickness owes its origin to the collisional thrusting of the Eastern Ghats Province against the Archean cratons. Significant variations in the nature of Moho are also noted. The flat sharp cratonic Moho is distinct from the gradational Moho below the Eastern Ghats Province, possibly a signature of magmatic underplating below the mobile belt. The nature of the lithosphere-asthenosphere boundary (LAB) interpreted from the gradient change in velocity appears to be poorly-resolved. Therefore, we utilise radial anisotropy determined from the discrepancy between VSH and VSV based on Rayleigh and Love-wave velocities respectively, as a proxy. Our findings confirm the LAB through positive radial anisotropy (VSH > VSV) prevalent in the asthenospheric-mantle that is likely explained by flow-induced shear. Overall, the lithospheric architecture below the study area has been shaped through several deformational episodes that distinguish the multiple litho-tectonic units within the mobile belt. The loss of cratonic lithospheric keel can be attributed to the mantle plume given the Gondwanan trajectory of the Indian subcontinent over Kerguelen and Crozet hotspots.