L'evoluzione permo-giurassica del Bacino di Diego-Suarez (Madagascar settentrionale) e dei margini occidentali del Madagascar e dell'Africa orientale

A revised model for the evolution of the East Africa-Madagascar conjugate margins and intervening oceanic crust is presented. The model incorporates available magnetic data, a reinterpretation of oceanic basement morphology in the Comore and Somali basins and analysis of structural features within the neighbouring continental areas. It is essentially an adaptation of previous models but proposes a three phase tectonic evolution rather than the single southward migration of Madagascar along the Davie and Dhow Fracture Zones envisaged in previous models. The three phases are as follows: Phase 1) NE-SW rifting: Late Carboniferous-Permotriassic rifting, with related strike-slip movements in connection with the main African Shear Zones (NE-SW trend). Phase 2) N-S rifting: Middle to Late Triassic (?) rifting along the eastern arm of a triple junction centred in northern Kenya which resulted in southward displacement of Madagascar between the Davie and the Dhow Fracture Zones. Phase 3) NNW-SSE drifting: Early to Middle Jurassic(?)-Aptian SSE drifting of Madagascar and limited rotation due a triple junction located to the south of Madagascar at the junction of the African, India-Madagascar and Antarctic-Australia plates. In this geodynamic reconstruction, Madagascar is restored very close to the coast of Kenya with its main axis approximately N-S, parallel to the Dhow fracture zone.