India and Madagascar in Gondwanaland based on matching Precambrian lineaments

Abstract

THE geometrical fit of Madagascar against India has been widely accepted in most reconstructions of Gondwanaland¹. This fit is consistent with Precambrian trends, lithologies and age provinces^2,3. Palaeomagnetic data also support the general fit of Madagascar against India⁴, and there are suggestions that this reassembly can be recognised as far back as Proterozoic times⁵. The exact fit of east Madagascar and west India has not been adequately defined. Recent knowledge of the Precambrian geology and tectonics, has now allowed the possibility of better defining this fit, mainly on the basis of matching Precambrian re-entrant lineaments. The east coastline of Madagascar is a rectilinear feature, with a narrow shelf of 25–50 km and an abrupt steep break in slope after the 1,000-m isobath. The proposed opposing coastline of west India is also rectilinear with a wider shelf of 100 km and a shelf break down to the 1,000-m isobath. The 1,000-m isobath of India was receded towards the coastline by removing the post drift sediments, according to the best available sections⁶. A 1:2,500,000 conical projection was used to prepare a distortion-free, equidistance base map of both Madagascar and India (Fig. 1).