Gravity modeling in the Central African Rift System, Sudan: rift geometries and tectonic significance

Abstract

Gravity data acquired over approximately 285,000 square kilometers in east-central Sudan reveal the presence of four major parallel NW-SE trending gravity lows. These anomalies are produced by covered rift basins that are considered to be part of the Central African Rift System. Anomaly separation shows that doming in the regional gravity field occurs over the locus of basin clusters, a feature interpreted to result from crustal thinning coupled with passive mantle uplift. Rift structure is dominated by asymmetric stacks of rotated fault blocks that are inferred to lie above low-angle, crustalor lithospheric-scale detachment surfaces. Calculations made from regional gravity models and seismic data indicate a cumulative crustal extension of approximately 12–14 km for the four rifts which have a combined width of approximately 210 km. The resulting average extension within the basins is approximately 6–7%. Geophysical and geological data indicate that regional subsidence has been the general epeirogenic response during and after rifting. Age of the main phase of rifting is considered to be Cretaceous, although the relative timing of rifting between the major basins is unknown. Truncation of the rift basins along their northwestern ends supports an earlier hypothesis that the Central African Shear Zone continues through this region of the Sudan.