Crustal structure based on gravity–magnetic modelling constrained from seismic studies under Lambert Rift, Antarctica and Godavari and Mahanadi rifts, India and their interrelationship

Abstract

Modelling of gravity and magnetic anomalies along selected profiles across the Lambert Glacier, Antarctica constrained from the results of deep seismic sounding (DSS) along a profile provide: (i) 6–7 km thick sediments of low density (2.35 g/cm 3) which represent Permian–Triassic sediments as they are exposed along the margins of this basin; (ii) high density (2.75 g/cm 3) and high susceptibility rocks with a stable natural magnetization of 0.025–0.035 gauss as the basement; (iii) a high density body (2.80 g/cm 3) along the western shoulder which may represent mid crustal granulite and charnockite rocks exposed in the Prince Charles mountains; (iv) a thin crust of 25 km with a high density (3.05 g/cm 3) and high velocity underplated lower crust. These signatures suggest that the Lambert Rift and the Amery ice shelf represent an active continental rift valley with signatures of magmatism. The adjoining Prydz Bay basin along the east coast of Antarctica is also characterized by 5–6 km thick Permian–Triassic–Cretaceous sediments with seaward dipping reflectors of basic volcanic rocks. The Godavari and the Mahanadi Gondwana rift valleys of almost same period and length (500–600 km) across the east coast of India are also characterized by Permian–Triassic–Cretaceous sediments of almost same density and thickness. The Mahanadi Basin depicts a thin crust (33–34 km) with a high density (3.00 g/cm 3) underplated lower crust similar to the Lambert Rift and a low density (2.65 g/cm 3) layer in the upper crust. It indicates substantial rift magmatism in the coastal part of the Mahanadi Basin and adjoining continental shelf which forms a part of the Early Cretaceous volcanic province of East India. As the east coast of India and Antarctica were juxtaposed together at the time of evolution of these rift valleys, the above similarities between them might be due to their common heritage. The signatures of magmatism in the Lambert Rift of Antarctica and the Mahanadi Basin of India indicate that the thermal source at the time of their evolution was located under the eastern part of East Antarctica which might be responsible for its uplift supplying sediments of same provenance and fossil record in these basins.