Reconstruction of Madagascar and Africa: Evidence from the Davie Fracture Zone and Western Somali Basin

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Abstract
New seismic reflection, gravity, and magnetic data from offshore East Africa allow the Davie Fracture Zone to be traced from ∼11°S to its intersection with the Kenyan coast at ∼2°S, constraining the relative motion of Madagascar and Africa. Seasat‐derived free air gravity anomalies and slope/rise positive magnetic anomalies observed in shipboard data help to locate the continent‐ocean boundaries (COB) off the shore of East Africa and Madagascar. Seismic reflection data further document a diapirprovince off Madagascar, presumably conjugate to that observed off Kenya and Somalia. The Dhow and Very Large Crude Carrier (VLCC) basement ridges are complex features and do not appear to be simple fracture zones owing their existence entirely to the separation of Madagascar and Africa. From these data we determine a predrift fit of Madagascar and Africa involving a 14.2° rotation of Madagascar to Africa about a pole at 10°N, 150°E. The geometry of the reconstruction adheres to seismic and potential field data indicating the oceanic nature and extent of the Comoros Basin and of the Somali Basin between Kenya and the Seychelles, and it does not conflict with onshore or offshore stratigraphy. Timing of the opening of the Western Somali Basin is constrained by Mesozoic marine magnetic anomalies and extrapolation to the interpreted COB and occurred between approximately 165 and 130 Ma.