Insights into the evolution of the volcanic margin of Western India and associated intracratonic rifts

The Western continental margin of India (which includes the offshore Kutch, Saurashtra, Bombay and Kerla Konkan basins) and the intracratonic rifts of NW India (Cambay, Narmarda and Barmer basins), formed as a result of series of rifting events associated with the break-up of Gondwanaland during the Mesozoic and Early Cenozoic. Rifting initiated along inherited Proterozic trends, and influenced the resultant basin geometries. All of these rifted basins have an associated volcanism, evident from the Deccan flood basalts, resulting from the Indian plate passing over the Reunion Plume during the Cretaceous-Paleocene. As a result much of the rifting of the western margin of India has been described as magmatic, however this is an over simplification.

We use observations from seismic reflection and potential field's data, simple isometric modelling, and subsidence studies to understand the basin/ crustal structure and geodynamics in both the onshore and offshore domains. In the offshore basins, features common to volcanic margins (including seaward dipping reflectors, volcanic intrusions, and eruptive centres) can be seen. Accompanying these volcanic features are major along strike variations crustal structure. These variations are coincident with changes in basement terrane onshore (indicative of tectonic inheritance), though may also -relate to the varying influence of the Reunion Plume. In the offshore Deccan age volcanism post-dates much of the initial rifting, and generation of accommodation. In contrast, initiation of the intracratonic rifting appears to be approximately contemporaneous with the Deccan volcanic event, and as a result, there is significant post-volcanic accommodation spaced created.

Understanding the relative timing of extension (and creation of accommodation space) and volcanism is key to the sedimentary fill history of the basins. In the intracratonic basins, rift initiation is interpreted as contemporaneous with the Deccan volcanism, whereas on the continental margin the volcanism post-dates the main period of rifting. This has implications for hydrocarbon prospectivity, in particular for defining the extent of stretched continental crust and syn-rift sedimentary section, and the thermal history of the region.