Geodynamic Reconstructions and Deep Crustal Structure Interpretation of the East Africa Margin, and Implications on the Margin Stratigraphic Architecture

Abstract

The East Africa margin is today one of the most prolific gas province of the world, with the recent major gas discoveries of the Rovuma complex in Mozambique together with the ones in offshore Tanzania. However, a large part of the margin is still undrilled, and remains a frontier exploration domain. The area is structurally complex, the margin being segmented by major transform fault zones, such as the Davie or the Mozambique ridges. The petroleum system efficiency is still debated at a regional scale, a major question being the occurrence, extension and quality of the potential source rocks in the basins. A key issue is the characterization of the continent-ocean transition which may control a syn-rift source-rock extension, and also the thermal regime of the margin. A regional study was then performed from wells and seismic data, to better understand the evolution and the architecture of the different segments of the margin. In South Kenya and Tanzania, the opening of the Somalia basin was driven by the southward motion of the India/Madagascar continent along the Davie Ridge Transform Fault Zone (TFZ). The rifting started during Lias, and the oceanic expansion ended during Aptian. Along the Davie TFZ, Upper Jurassic / Neocomian pull-apart basins were formed then later inverted. In the oceanic domain, the mantle was first exhumed and then the oceanic crust was also lately structured along the different segments of the TFZ. In Mozambique, the rifting between the African craton and Antarctica also started during Lias. A volcanic margin was formed at that time all along the Mozambique coast westward of the Davie TFZ. Seaward Dipping Reflectors associated to an intense volcanism can be seen both in the onshore and offshore settings. Outboard of the Zambezi delta, the Beira high formed a prominent basement structure, an aborted rift separating the high from the African craton. During the oceanic expansion, which still continues, the basin was also sliding along the Mozambic ridge which was the site of alternating subsidence and inversion episodes. During Miocene times, the opening of the East African Oligo-Miocene rift systems induced changes in the stress regime both in the Somalia and Mozambique basins, and most of the structures were reactivated. The presentation will be illustrated by regional transects all along the margin from Kenya to Mozambique, in which both the margin structure and the sedimentary system architecture will be commented.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015