LITHOSPHERE-SCALE 3D STRUCTURAL MODEL OF THE SOUTHWEST AFRICAN PASSIVE CONTINENTAL MARGIN

The Southwest African continental margin is a passive volcanic margin where the Early Cretaceous continental break-up resulted in the formation of oceanic lithosphere within the Atlantic Ocean. To understand the present-day structure of the Southwest African margin, a 3D structural model has been constructed. This lithospheric-scale 3D model includes eight layers: (1) Sea water, (2) Cenozoic, (3) base Turonian-base Cenozoic, (4) base Aptian-base Turonian, (5) pre-Aptian sediments, (6) crystalline crust, (7) high-velocity/high-density lower crustal body and (8) lithospheric mantle.

During the model construction, the structural depth maps from Stewart et al. (2000) have been used for the Walvis and the Luderitz basins. For the Orange Basin, the main dataset consists of structural depth maps from Hartwig et al. (2010). A 3D lithospheric-scale model of the Southwest African margin (Hirsch et al., 2009) was the main data source for the crystalline crust and the upper mantle.

The Cenozoic is characterized by two zones of thick sediments within the Walvis Basin and the northern part of the Orange Basin. The thickness distribution of the Turonian-base Cenozoic interval indicates that the major depocentres are located within the Orange Basin. The Orange Basin is also characterized by thick Aptian-Turonian sediments. The thickness pattern of pre-Aptian sediments is relatively complex, showing pronounced thickness maxima in the Orange Basin.

The high-velocity/high-density lower crustal body has a NW-SE elongated shape restricted to the axial part of the margin. In general, the thickness of the crust and of the lithosphere decreases towards the oceanic crustal domain with some local variations.

References

Hartwig, A. et al.., 2010. Characterization of hydrocarbon generation and migration dynamics based on seismic interpretation and basin modeling: an integrated study of the Orange Basin, South Africa. AAPG Search and Discovery Article #90108, AAPG International Convention and Exhibition, Calgary, Canada.

Hirsch, K.K. et al., 2009. A lithospheric 3D temperature study from the South Atlantic. EGU General Assembly: Geophysical Research Abstracts, Vol. 11, EGU2009-8053, Vienna, Austria.

Stewart, J. et al, 2000. Three-dimensional subsidence analysis and gravity modelling of the continental margin ofshore Namibia. Geophys. J. Int., 141, 724-746.