Folding of Oceanic Crust Along the Davie Fracture Zone, Offshore Tanzania

The Davie Fracture Zone (Davie FZ)—among the longest offshore transform systems in East Africa—mediated Madagascar’s southward displacement following Gondwana’s Early Jurassic breakup. This giant structure has a distinct topography and gravity field signals. However, it is buried by thick sediments in its northern segment offshore Tanzania, hindering understanding of the internal structures and their origin. In this study, we applied 2-D multichannel seismic to analyze the structural characteristics and evolution of the Davie FZ. The Davie FZ is located in the oceanic domain, which is bordered by the landwards-dipping overthrust fault at the continent–ocean boundary. Volcano sediments atop the basement with undulating Moho reflection below depict a typical oceanic domain. Distinct compressive deformation characterized by the crustal undulation of around 40 km wavelength forms folded oceanic crust, and Late Jurassic sediments onlap onto the crest of the folded basement. The Davie FZ is localized in a corridor with the thickened oceanic crust and is presented by positive flower structures with faulted uplifted basement and deepened Moho. The Davie FZ evolved from a proto-transform fault located in Gondwana before the spreading of the West Somali Basin. During the Late Jurassic, a kinematic change shifted the spreading direction from NW–SE to N–S, resulting in a strike-slip of the Davie FZ and contemporaneous transpressional deformation offshore Tanzania. The Davie FZ is an excellent case to understand the tectonic-magmatic process forming this transform margin.