SOME GEODYNAMIC ASPECTS OF THE KRISHNA-GODAVARI BASIN, EAST-COAST OF INDIA

Detailed analysis of magnetic data of the Krishna-Godavari offshore basin provides new information on the evolution of this basin since the breakup of Peninsular India in the late Jurassic from the erstwhile Gondwanaland. The results establish the offshore extension of two major onshore cross trends viz, the Chintalapudi and Avanigadda cross trends (CCT and ACT). While the onshore basin is characterized by NE-SW ridges and depressions, the offshore basin is divided essentially into three segments by these two NW-SE cross trends. The Ocean-Continent Boundary (OCB), located at the foot of the continental slope of this region, appears to be the seaward limit of these two cross trends. An isolated source of high magnetic intensity (a hot spot?) is identified near the OCB of Machilipatnam, confined between the two cross trends. The Pranhita Godavari Gondwana graben, located north of CCT, extends into the offshore along two faulted cross trends, viz, the CCT and the newly identified Yanam cross trend. The weak magnetic signature associated with this graben at greater depths in the offshore is probably due to flexural subsidence. Preliminary reconstruction of the evolutionary stages of this basin suggests that the hot spot (Marion ?) with its trace located at the OCB represents the earliest stage of the breakup of east coast of India in the late Jurassic (126 Ma), although the relation between this hotspot and the two cross trends on either side remains unresolved. The breakup was associated with rift phase volcanism, as evidenced by the inferred dyke intrusions in the Nizampatnam bay in the southern part of the basin. The Pranhita Godavari Gondwana graben formed due to this split, pull apart and the subsequent downwarping of the eastern continental margin, appears to be much deeper and wider in the offshore. The NE-SW ridges (Tanuku, gaza and Bapatla) and the depressions (East and West Godavari and Krishna) of the onshore basin are a consequence of the post-rift vertical tectonics associated with the evolution of this passive margin.