Somali Basin's Crustal Structure and Post-Rift Deformation: A Recorder of Madagascar and India Drifts

Abstract

The opening of the West Somali Basin between Madagascar and east Africa in Late Jurassic-Aptian is recorded in the oceanic domain by NE-SW to E-W trending magnetic anomalies M25 to M10. Thanks to petroleum exploration, its western continental margin is now imaged by deep seismic: i.e. the Davie Transform Zone (DTZ), the Kenya-Tanzania oblique segments to the South and the Kenya-Somalia divergent segment to the North. The whole margin has experienced various postrift tectonic reactivations that can now be illustrated. The Somali rifted margin has formed at the expense of the thick cratonic Karoo Basin. It is a typical magma-poor margin much alike the well-known type described in the Iberia to the Alps. The crustal structure of the Kenya-Tanzania margin is difficult to decipher due to poor seismic quality in the continental domain. The well-imaged proximal oceanic basin is made of both volcanic and mantle rocks, derived from the early rifting and from the formation and evolution of the DTZ. During the opening of the Somali Basin, from Late Jurassic to Aptian, the DTZ accommodated the southward drift of Madagascar. Along the wide sheared corridor of the DTZ, N-S to NW-SE thrust affected the oceanic crust during the Hauterivian-Barremian while spreading was still active in the basin. The Davie trend is again reactivated in the Late Cretaceous-Paleogene with the large inversion of the Neocomian Anza Graben to the North. The Kerimba Trough in Tanzania is a Miocene sinistral pull-apart reactivation along the DFZ coeval with the onset of the Comoros volcanism. Sinistral movements still occur along the DTZ as well as normal faulting between Zanzibar and Pemba Island and the coast. This activity features the incipient Rovuma plate. A structural map, some cross-sections and a tectonic calendar are proposed to illustrate the different crustal domains and the history of a margin which never really became passive. The post-rift events are tentatively correlated with the evolution of the Somali and younger basins that could have formed as a consequence of the Indian break-up and drift and possibly other remote kinematic events.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018