East African Rift System plate geometries and surface motions are some of the least constrained in the context of global plate motion models. In this study, we used GPS data to constrain Somalian plate rotation and to suggest a new tectonic plate geometry for the region. In addition, we tested geologic data from the Southwest Indian Ridge and new GPS data on Madagascar to determine refined kinematics of the Lwandle microplate. A zone of broad deformation was discovered, extending from the eastern boundary of the Rovuma microplate, across the Comoros Islands, and including parts of central and northern Madagascar. Madagascar is fragmenting, with southern Madagascar rotating with the Lwandle microplate and a piece of eastern and south-central Madagascar moving with the Somalian plate. Divergence of the Nubian-Somalian plate system across the East African Rift System involves both diffuse deformation and strain accommodation along narrow rift segments that bound rigid blocks.

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