India-Madagascar Separation: Breakup Along a Pre-existing Mobile Belt and Chipping of the Craton

Abstract

Separation of India from other parts of the Gondwanaland during the past ∼150 m.y., can be characterized by the thermomechanical interaction between the continental lithosphere, particularly its mobile belts, and mantle plumes. It implies that, a combination of mobile belts and plumes could be often ‘fatal’ for supercontinental stability. For example, the Eastern-Ghat mobile belt (EGMB) and Kerguelen/Crozet hotspots together seem to have facilitated India's separation from Antarctica. In view of this, and on the basis of geophysical and other closely related data sets, it is suggested here that prior to ∼90 Ma, Madagascar, along with the westernmost margin of the South Indian shield, was also a part of the mobile belt network of India. The latter consists of Eastern-Ghat, Southern Granulite Terrain, Satpura and Delhi-Aravalli mobile belts. It implies that the India-Madagascar breakup (at ∼90 Ma) would have also taken place along a relatively mobile corridor under the influence of Marion plume. This is supported by the fact that the gravity anomalies, Moho depths, tectonics, and seismic deformations over the mobile belts of India and the Madagascar are quite similar. The study also brings out that the combination of geophysical anomalies and geological features may allow better constraining of India-Madagascar juxtapositioning. Along the eastern margin of the Madagascar, there exist two thin (∼25-75 km wide, nearly N-S trending) low-grade strips of Archaean age crust, viz. the Antongil block (in northeast) and the Masora block (central-eastern part), which are bounded to the west by the Betsimisaraka suture zone (BS). These represent the westernmost boundary of the Dharwar craton, and appear to have been chipped off during the separation of India and Madagascar, because of the weakening of westernmost margin of the Dharwar tectosphere due to episodic deformation and metamorphism in Madagascar. Continental breakup along the mobile belts and chipping of cratonic margins appear to be globally applicable.