--> Abstract: Structure and Tectonic Evolution of the Eastern Continental Margin Basins of India, by S. K. Biswas and A. Agrawal; #91012 (1992).

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ABSTRACT: Structure and Tectonic Evolution of the Eastern Continental Margin Basins of India

BISWAS, S. K., and ABINASH AGRAWAL, Oil and Natural Gas Commission, Dehradun, India

The Mesozoic rift basins on the eastern continental margin of India (Cauvery, Palar, Krishna-Godavari or KG, Mahanadi, and Bengal) came into existence as a result of Late Jurassic fragmentation of the eastern Gondwanaland into India, Antarctica, and Australia, and they are separated from each other by intervening basement promontories. The promontory-depression alternation of this margin could be broadly comparable to "salient-embayment" couplet in the simple shear, conjugate margin model of passive margin development.

Detailed structural mapping at basement level in the Cauvery, Palar, and KG basins, and to some extent in the Mahanadi and Bengal basins, indicate that they are subdivided into northeast-southwest-oriented horst-graben features. During the Late Jurassic rifting, the pre-existing, northeast-southwest structural grain in the Precambrian Eastern Ghat crust may have aided parallel development of the northern segment of this continental margin, on which the Bengal, Mahanadi, and KG rift basins are located. The southwestward propagation of rifting along the northern segment appears to have terminated in the Palar basin and changed direction to continue north-south probably as a transform boundary, presumably guided by a change in the strength of granulitic crust undergoing stretching/attenu tion.

The sedimentary basins along the north-south, Coromandel margin of India (Cauvery and Palar) are characterized by: (1) rhomb-shaped grabens, bordered by marginal plateaus (Vedaranyam and Madras highs) on the seaward side, and (2) limited crustal attenuation, and associated smaller tectonic subsidence and heat-flow in the basins. A pull-apart kinematic model is envisaged for the syn-rift origin of the Coromandel margin basins of India, associated with right-lateral strike-slip motions between India and Sri Lanka. Larger and stronger right-lateral motions along the main zone of continental breakup between India and Antarctica (which lies to the east of marginal plateaus and outside these basins) may have allowed only secondary strike-slip motions between India and Sri Lanka, and pull-ap rt initiation of these basins during syn-rift history of the Coromandel margin of India. The Early Cretaceous volcanism in the Bengal basin (Rajmahal traps) as well as in the Cauvery basin (Mannar volcanics) and mapping of a regional "breakup" unconformity may be related to an Early Cretaceous (Aptian) continental breakup between India and Antarctica.

The relatively narrow eastern margin of India was significantly affected by tectonism in terms of the Cenozoic reactivation of the major pre-existing structural joins/discontinuities in the crust, and the initiation of the Bengal foreland. This was associated with counterclockwise rotation of India, followed by India-Asia collision and continental-subduction across the Himalayan and the Indo-Burmese orogens.

 

AAPG Search and Discovery Article #91012©1992 AAPG Annual Meeting, Calgary, Alberta, Canada, June 22-25, 1992 (2009)