Geophysical Structure of Western Offshore Basins of India and its Implications to the Evolution of the Western Ghats

Western Ghats lies to the east of two prominent basins of western offshore viz( 1 ) Mumbai offshore basin (2) Konkan-Kerala offshore basin. These basins have evolved in a divergent continental margin setting as a consequence of break up of Madagascar in Mid Cretaceous and Seychelles in Late Cretaceous from Indla. The basic framework of the Western Continental Margin of India was established by the end of Cretaceous.

The Surat depression in the north and the Vengurla Arch in the south define Mumbai offshore basin. Shelf marglin basin marks its western limit. The width of the shelf is -230 km. The entire shelf from the coast towards the shelf margin zone is segmented by basement controlled NW-SE to N-S faults giving rise to many horst graben features. The Konkan-Kerala basin located south of the Vengurla Arch has an average width of - 75 km. Eastern fringe of the basin extends to the land along the Kerala coast where outcrops of Miocene are preserved. In the west a number of NNW-SSE trending Laxmi-Laccadive and Koil-Comorin ridges separated by depressions are identified. The basin is more differentiated in Eocene/Oligocene section with N-S trending horsts and grabens.

The seismic data in the basins show prominent N-S fault trends. The data further indicate the presence of strike-slip movement and associated flower structures. Therefore, the geophysical and drillng data in the western offshore support a plate tectonic model for structural styles as a result of fragmentation initliated by transform faulting. The basins came into existence in late Cretaceous and evolved through Tertiary. Extensive lava flows at 65 Ma are attributed as a fissure type eruption through transform faults during Deccan volcanism. The Western Ghats may therefore, be the result of rifting and severe faulting with initial uplift and tilt to the east. The west coast of India was further elevated during the Tertiary in successive phases. The removal of vast quantities of rocks from the onshore its deposition in the offshore basins and the associated flexuial responses might have resulted in the present day Western Ghats escarpment.