Lithosphere structure and evolution of the Southern Indian Shield: Constraints from 2-D joint potential field modelling, seismological and geochronological data

Abstract

The Southern Indian Shield comprises the Bastar and Dharwar cratons, the Southern Granulite Terrain, the Eastern Ghat Mobile Belt, and the Pranahita Godavari and Cuddapah rift basins. Multiple amalgamations and large igneous provinces related to magmatism during the Archean to Proterozoic times significantly modified the lithosphere in this region, making it difficult to infer the structure and geological history. This necessitated the delineation of lithosphere structure through geophysical data. In this study, 2D joint potential field modelling constrained by seismic and seismological data is performed to delineate the lithospheric structure below the Southern Indian Shield region. The constrained potential field models reveal: i) Cuddapah Basin, Southern Granulite Terrain, and Eastern Ghats Mobile Belt regions are characterized by higher density crust, ii) a mid-crustal low-density layer below Dharwar and Bastar cratons, iii) deeper Moho below Pranahita Godavari and Cuddapah basins, iv) a comparatively thin lithosphere below Dharwar Craton; and v) relatively deeper lithosphere beneath Southern Granulite Terrain − Dharwar Craton boundary region. The high-density, thicker crust and shallow lithosphere beneath the Cuddapah Basin and the Eastern Ghat Mobile Belt have resulted from large igneous province events at ca 2200 Ma and 1800 Ma, followed by lithospheric metasomatism at ca 1000 Ma. The shallow Lithosphere-Asthenosphere Boundary beneath Pranahita Godavari graben reflects Proterozoic rifting and further reactivation during Gondwana breakup. The deeper Lithosphere-Asthenosphere Boundary beneath the Southern Granulite Terrain-Dharwar Craton boundary is attributed to orogenesis caused by subduction events between 780 Ma and 550 Ma. The distinct crustal structure, magnetisation, and shallow Lithosphere-Asthenosphere Boundary in the Dharwar Craton region are inferred to have resulted from amalgamation events during the Archean, overprinted by Proterozoic large igneous province events at ca 2200 Ma and 1800 Ma.