Neoproterozoic deformation in the northeastern part of the Saharan Metacraton, northern Sudan

Abstract

The northeastern part of the Saharan Metacraton is dominated by medium to high-grade gneisses and migmatites, disrupted by belts of low-grade volcano-sedimentary sequences representing arc assemblages and highly dismembered ophiolites, and intruded by A-type granitoids. This part of the Saharan Metacraton is affected by three Neoproterozoic deformation events: (1) Emplacement of S- to SE-verging nappes of ophiolites and passive margin sediments. The most prominent of these nappes is the Atmur-Delgo fold and thrust belt which extends westward from the eastern margin of the Saharan Metacraton to just east of the Third Cataract Nile. This belt is interpreted as manifesting the closure of a restricted oceanic basin between the Bayuda and Halfa Terranes at ∼700–650 Ma. (2) Development of N- to NE-trending folds as a result of E-W shortening that accompanied NW-SE oblique collision between the Saharan Metacraton and the Arabian-Nubian Shield at ∼650–590 Ma. This event, although dominantly localized along the Keraf Suture at the boundary between the Saharan Metacraton and the Arabian-Nubian Shield, also resulted in deformation within the northeastern part of the Saharan Metacraton. N- to NE-trending folds occur either as broad belts (Wadi Halfa Fold Belt) or narrow and discrete zones (Third Cataract Shear Zone). Thrust stacking and folding thickened the Saharan Metacraton lithosphere as shown by numerous gneissic domes, such as the Delgo Dome, in the northern part of the Bayuda Terrane. Crustal thickening also generated A-type granitoids that intrude the northeastern part of the Saharan Metacraton. E-W shortening culminated in the development of ∼590–550 Ma, N- to NNW-trending sinistral strike-slip shear zones, sometimes coinciding with the N-trending fold belts as in the case of the Third Cataract Shear Zone. (3) Thickening of the Saharan Metacraton lithosphere triggered orogenic collapse with N-trending moderate-angle normal-slip faults developed after 550 Ma. Neoproterozoic deformation and igneous activity in the northeastern part of the Saharan Metacraton are interpreted as due to processes that involve collision, lithospheric mantle delamination, and regional extension.