The position of Madagascar within Gondwana and its movements during Gondwana dispersal

A reassembly of the Precambrian fragments of central Gondwana is presented that is a refinement of a tight reassembly published earlier. Fragments are matched with conjugate sides parallel as far as possible and at a distance of 60–120 km from each other. With this amount of Precambrian crust now stretched into rifts and passive margins, a fit for all the pieces neighbouring Madagascar – East Africa, Somalia, the Seychelles, India, Sri Lanka and Mozambique – may be made without inelegant overlap or underlap. This works less well for wider de-stretched margins on such small fragments. A model of Gondwana dispersal is also developed, working backwards in time from the present day, confining the relative movements of the major fragments – Africa, Antarctica and India – such that ocean fracture zones collapse back into themselves until each ridge-reorganisation is encountered. The movements of Antarctica with respect to Africa and of India with respect to Antarctica are defined in this way by a limited number of interval poles to achieve the Gondwana ‘fit’ situation described above. The ‘fit’ offers persuasive alignments of structural and lithologic features from Madagascar to its neighbours. The dispersal model helps describe the evolution of Madagascar’s passive margins and the role of the Madagascar Rise as a microplate in the India–Africa–Antarctica triple junction. Intrusions, extrusions and dykes observed in Madagascar and its neighbours, largely from aeromagnetic survey data, are related to the outbreak of the Karoo/Bouvet mantle plume at ~182 Ma, the Marion mantle plume at ~88 Ma and the Reunion mantle plume at ~66 Ma. The dispersal model may be viewed and downloaded as an animation at: http://www.reeves.nl/gondwana.