The Rovuma Transform Margin: locating East Africa's transform continent-ocean transition

Understanding the nature and location of paleo-plate boundaries is fundamental to building accurate plate tectonic reconstructions, and therefore to our understanding of continental breakup processes. Here, we use seismic reflection data and three gravity modelling techniques to reveal the location of the East African continent-ocean transform margin, a first-order tectonic feature of the Earth. We find the ‘Rovuma Transform Margin’ is situated along the Rovuma Basin between Mozambique and Tanzania. The margin displays a rapid transition between continent and ocean, with up to 29 km of crustal thinning occurring over as little as 17 km, indicating Moho slopes across the necking zone of up to 83˚. The Rovuma Transform Margin strikes NNW-SSE, ~parallel to the onshore basement outcrop along the Rovuma Basin, and deviates from the Davie Fracture Zone at 13˚S. Beneath the Rovuma Delta, the Rovuma Transform Margin and continent-ocean transition may pass onshore, a result of post-breakup oceanward growth of the Rovuma sedimentary delta over the margin. The Jurassic age of the oldest Rovuma Basin sediments indicates the transform margin developed as a new structure during Gondwana breakup, indicating structural reactivation played a minor role in this major transform’s development. The Rovuma Transform Margin played a key role in Gondwana dispersal and its newly constrained position supports an origin for Madagascar within the Tanzania Coastal Basin, indicating a ‘tight-fit’ reconstruction of Gondwana fragments prior to the Jurassic. These findings have important implications for our understanding of transform fault development and evolution, plate tectonics, and supercontinent breakup processes.