A Gondwanan micro-fragment adjacent to southern granulite terrane of India: Evidence from satellite gravity studies

The Southern Granulite Terrane (SGT) of Peninsular India is a complex collage of Mesoarchean to Late Neoproterozoic - Cambrian tectonic units, which were part of Earth's major supercontinents such as Ur, Columbia, Rodinia, Gondwana and Pangea. We analyzed high-resolution satellite gravity field with a view to demarcate the underlying crustal and lithospheric mantle structure of the SGT. The western part of SGT is characterized by a high-order elongated negative residual gravity anomaly of -80 mGal together with a thicker Moho (43 km) and the lithosphere (-130 km). In comparison, in the central and eastern parts of SGT, the gravity anomalies are distinctly positive, Moho is shallow (-36 km) and the lithosphere is thin (-100 km). An important finding of the present study is the delineation of a fragmented micro-continental block of the SGT, submerged under Indian Ocean, and located about 30 km west of the rifted continental margin of India, which is characterized by moderate crustal seismicity, and high-order gravity low of -80 mGal, identical to the features of western SGT. This distinct micro-block might represent a vestige of the rifting between India and Madagascar at around 90 Ma due to upwelling of the Marion mantle plume and marking the final breakup of the Gondwana assembly.