Active Microplate Boundaries Associated With the Southward Offshore Extension of the East African Rift System and the Distribution of Offshore Hydrocarbon Discoveries in East Africa

Abstract

Numerous giant gas fields have been discovered over the last decade in the East African area of offshore Mozambique and Tanzania - most notably Anadarko's ∼150 TCF gas discovery within the Rovuma delta of Tanzania. In this hydrocarbon-rich region, GPS-based studies of active plate motions have constrained the locations of three active microplates (Victoria, Rovuma, and Lwandle) with the latter two occupying an offshore corridor driven by the formation of the East African rift system. These GPS models predict varying boundaries and kinematic behaviors of the Rovuma and Lwandle microplates in the areas of Tanzana, Mozambique and Madagascar that include pure E-W extension, NW-SE extension, radial extension, and microplate development that allows for simultaneous extension and compression at different locations around the plate boundary. In this study we use a compilation of earthquakes, earthquake focal mechanisms, geologic maps, gravity and magnetic maps, and seismic reflection data to test the proposed boundaries, rotation direction, and rifting styles associated with the proposed Rovuma microplate of onland and offshore Tanzania and Mozambique. Earthquake focal mechanisms and basin development on the eastern and western sides of the microplate suggest modern day extensional tectonics, while seismic interpretations along the northern margins indicate Quaternary-recent(?) transpressional tectonics. Our data compilation indicates that significant microplate rotation effects are not observed; instead all microplates areas reflect uniformly EW extension. The linear trend of gas giants in the Rovuma delta are aligned along the proposed northeastern margin of the Rovuma microplate. Opening along the microplate boundary may contribute to higher heatflow and maturation in this deltaic setting.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016