India-East Antarctica conjugate margins: rift-shear tectonic setting inferred from gravity and bathymetry data

The Eastern Continental Margin of India (ECMI) has evolved as a consequence of breakup of India from East Antarctica during the Early Cretaceous (ca. 130 Ma). The conjugate margin of ECMI in East Antarctica is represented by the margin extending from Gunneris Ridge in the west to about 95 degreesE i n the east. To understand the isostatic compensation mechanism operating be neath these conjugate margins, we have examined the cross spectral correlat ion between gravity and bathymetry along 21 profiles across the ECMI and 16 profiles across the conjugate East Antarctica Margin using both ship and s atellite-derived gravity data. The ECMI is considered as a composite of two segments, one north of 16 degreesN extending beyond 20 degreesN, which is based on its rifted margin character, and the other, south of 16 degreesN e xtending up to Sri Lanka, which has a transform-rift character. Similarly, the conjugate margin of East Antarctica is also considered to be a composit e of two segments, west and east of the central bulge at 50-55 degreesE. Ad mittance analysis and comparison with various isostatic models suggest a fl exural plate model with an elastic thickness of 10-25 km for the northern s egment of ECMI and its conjugate segment which is the east Enderby land Mar gin, comparable to results obtained from the eastern North American Margin. For the southern segment of ECMI, low elastic plate thickness of less than 5 km or a local compensation is obtained with matching results for the wes t Enderby land Margin. These, in turn, appear comparable to the low T-e val ues inferred for the Ghana transform margin of North Africa and Grand Banks Margin of eastern Canada, thereby indicating that the southern segment of ECMI and its conjugate in East Antarctica have developed as a consequence o f shearing rather than rifting in the early stages of continental separatio n. (C) 2001 Elsevier Science B.V. All rights reserved.