LITHOSPHERIC EXTENSION NORTHWEST OF THE CENTRAL AFRICAN SHEAR ZONE INSUDAN FROM POTENTIAL-FIELD STUDIES

The Central African Shear Zone (CASZ) is a 4000-km-long, NE-striking w rench fault system, along which motion occurred during the break-up of Gondwanaland, but its location in central Sudan was poorly defined. P rior to this study, it was thought that Mesozoic extension was restric ted to Sudan south of the mapped and proposed location of the CASZ. We use nearly all gravity data from Sudan, including 1894 unpublished gr avity points in eastern Sudan to (1) clarify the position of the CASZ in central and eastern Sudan and to (2) interpret anomalies northwest of the CASZ with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 t o occur southeast of the CASZ. Considering the dimensions of these gra vity minima and existing geological, aeromagnetic, magneto-telluric, s eismic and well data, we suggest that fault-bounded sedimentary basins lie north of the CASZ in central and eastern Sudan. We construct geol ogical models of the Bara, Bagbag, Humar, Gilif and Abu Dulu rift basi ns to investigate the subsurface geometry of these previously undetect ed basins, constraining models with existing geological and geophysica l data. The detrended gravity profiles can be fit by 40-60-km-wide bas ins bounded on one or both sides by normal fault systems, and with dep ths 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 be en considered, The < 10 km cumulative Mesozoic extension within the Af rican plate north of the CASZ implied by these studies, however, will not change significantly current plate models for the break-up of Afri ca and South America.