Architecture, structural and tectonic significance of the Seagap fault (offshore Tanzania) in the framework of the East African Rift. (28th October 2022)

• Record Type: Journal Article
• Authors: Iacopini, David; Tavani, Stefano; Pentagallo, Sara; Maselli, Vittorio; Dottore Stagna, Marina; Ebinger, Cynthia; Reynolds, David; van Vliet, Arjan
• Is Part Of: Basin research. Volume 35:Number 1(2023)
• Page Start: 387
• Page End: 412
• Publication Date: 2022-10-28
• Subjects: East African Rift -- marine geology -- Seagap fault -- seismic data interpretation -- tectonic -- West Somali basin; Sedimentation and deposition -- Periodicals; Sedimentary basins -- Periodicals; 551
• DOI: 10.1111/bre.12716
• Languages: English
• ISSNs: 0950-091X

Abstract

Abstract: The Southeastern portion of the East African Rift System reactivates Mesozoic transform faults marking the separation of Madagascar from Africa in the Western Indian Ocean. Earlier studies noted the reactivation of the Davie Fracture Zone in oceanic lithosphere as a seismically active extensional fault, and new 3D seismic reflection data and exploration wells provide unprecedented detail on the kinematics of the sub‐parallel Seagap fault zone in continental/transitional crust landward of the ocean‐continent transition. We reconstruct the evolution of the seismically active Seagap fault zone, a 400‐km‐long crustal structure affecting the Tanzania margin, from the late Eocene to the present day. The Seagap fault zone is represented by large‐scale localized structures affecting the seafloor and displaying growth geometries across most of the Miocene sediments. The continuous tectonic activity evident by our seismic mapping, as well as 2D deep seismic data from literature, suggests that from the Middle‐Late Jurassic until 125 Ma, the Seagap fault acted as a regional structure parallel to, and coeval with, the dextral Davie Fracture Zone. The Seagap fault then remained active after the cessation of both seafloor spreading in the Somali basin and strike‐slip activity on the Davie Fracture Zone, till nowaday. Its architecture is structurally expressed through the sequence of releasing and restraining bends dating back at least to the early Neogene. Seismic sections and horizon maps indicate that those restraining bends are generated by strike‐slip reactivation of Cretaceous structures till the Miocene. Finally based on the interpretation of edge‐enhanced reflection seismic surfaces and seafloor data, we shows that, by the late Neogene, the Seagap fault zone switched to normal fault behaviour. We discuss the Seagap fault's geological and kinematic significance through time and its current role within the microplate system in the framework of the East African rift, as well as implications for the evolution and re‐activation of structures along sheared margins. The newly integrated datasets reveal the polyphase deformation of this margin, highlighting its complex evolution and the implications for depositional fairways and structural trap and seal changes through time, as well as potential hazards. Abstract : Seagap fault zone, is a 400‐km‐long crustal structure affecting the Tanzania margin probably since the mid Jurassic. By the late Eocene till early Neogene, the Seagap fault acted as a sinistral strike slip fault producing releasing and restraining bend structures. Seafloor seismic maps suggest by the late Neogene, the Seagap fault zone switched to normal fault behaviour.