Role of Structural Inversion along the East African Passive Continental Margin

The East African margin has been historically thought to be a passive margin since the rifting of Madagascar from East Africa in the Middle Jurassic. However, the presence of anticlinal folds that create large offshore islands of Pemba and Zanzibar is peculiar suggesting that the evolution of the East African continental margin is more complex. New seismic data allows these structures to be understood for the first time. Results of our studies demonstrate that the folds were created by punctuated contractional deformation associated with fault reactivation and basin inversion during the Early Oligocene and Late Miocene. Whilst the structural inversion appears to be mild and the faults are still in net extension, they have clearly created enough relief to create the large offshore islands seen today. Compression in the area has continued to the present day, evidenced by deformation at the seabed. Given that the timing of the contractional deformation that formed the island anticlines are coeval with the onset of the East African Rift System, it appears to be the likely driver for this long-lived yet punctuated tectonism. However, equally crucial is the occurrence of the Davie Ridge, which creates the eastern buttress for strain to accrue between.