Lithospheric extension northwest of the Central African Shear Zone in Sudan from potential field studies

Abstract

The Central African Shear Zone (CASZ) is a 4000-km-long, NE-striking wrench fault system, along which motion occurred during the break-up of Gondwanaland, but its location in central Sudan was poorly defined. Prior to this study, it was thought that Mesozoic extension was restricted to Sudan south of the mapped and proposed location of the CASZ. We use nearly all gravity data from Sudan, including 1894 unpublished gravity points in eastern Sudan to (1) clarify the position of the CASZ in central and eastern Sudan and to (2) interpret anomalies northwest of the CASZ with similar trends and amplitudes as those basins known to occur southeast of the CASZ. Considering the dimensions of these gravity minima and existing geological, aeromagnetic, magneto-telluric, seismic and well data, we suggest that fault-bounded sedimentary basins lie north of the CASZ in central and eastern Sudan. We construct geological models of the Bara, Bagbag, Humar, Gilif and Abu Dulu rift basins to investigate the subsurface geometry of these previously undetected basins, constraining models with existing geological and geophysical data. The detrended gravity profiles can be fit by 40–60-km-wide basins bounded on one or both sides by normal fault systems, and with depths of 1.5–3.5 km. These patterns suggest that the CASZ in central and eastern Sudan is a broader zone of deformation than had previously been considered. The < 10 km cumulative Mesozoic extension within the African plate north of the CASZ implied by these studies, however, will not change significantly current plate models for the break-up of Africa and South America.