High-Resolution Imaging of the Crust Beneath the Proterozoic Aravalli–Delhi Fold Belt in Northwestern India: Evidence of Anomalous Crustal Thickening

Abstract Evolutionary models for the Proterozoic Aravalli–Delhi fold belt (ADFB) in northwestern India are debatable due to the nonreflective crust resulting in a partially resolved crustal structure, poor imaging of the Moho, and ambiguity in the subduction polarity. Receiver function (RF) analysis was done using ≈5000 RFs from 30 broadband stations spaced at intervals of ≈10 to 12 km along a 250-km-long northwest–southeast traverse across the ADFB. High-resolution common conversion point imaging was performed using the VP/VS ratios (κ) and the 1D shear-wave velocity (VS) models estimated from H−κ stacking and neighbourhood inversion, respectively. The geometry and continuity of the Moho and the intracrustal layers beneath the ADFB are imaged with better resolution than the earlier studies. The Delhi Fold Belt (DFB), located between the Marwar basin (MB) and the Banded Gneissic Complex (BGC), is characterized by an anomalously thick (≈52 km) crust, a southeast-dipping Moho, a domal midcrustal interface, and a mafic lower crust with VS≥4 km/s. In contrast, MB is underlain by a thin (≈38 km) felsic crust, and BGC is predominantly characterized by a felsic crust with thickness increasing from ≈38 to ≈45 km toward DFB. The feasible mechanisms of crustal thickening, such as magmatic underplating, relamination, and crustal shortening, are examined within the framework of ensialic and plate tectonic models. The convergence between the Marwar and Aravalli cratons led to the subduction of the intervening oceanic crust, possibly comprising island arcs, which were detached, melted, and relaminated to the base of the crust, followed by crustal accretion and shortening due to collisional tectonics. The mafic residue of the rift-related magma and fractionated melts forms a high-velocity lower crust, resulting in a rheologically strong, thick crust beneath DFB.