Obliquely convergent tectonics and granite emplacement in the Trans-Saharan belt of Eastern Nigeria:: a synthesis

The Eastern Nigeria terrane belongs to the 3000 km-long Trans-Saharan belt which was formed in the Neoproterozoic, between 750 and 500 Ma by continental collision between the converging West African craton, Congo craton and East Saharan block. The study area consists mostly of gneisses and migmatites that underwent granulite facies metamorphism (> 800 degreesC, 800 MPa). In contrast with Western Nigeria and Cameroon, no basement-cover relationship has been identified which is in agreement with a monocyclic metamorphic history. Around 640 Ma, the area underwent a nappe tectonics with eastward displacement, emplacement of Bt-Ms granites and granulite facies peak, Later on, around 615 Ma. nappes were towards the north. Numerous Hbl-Bt granite plutons were emplaced around 585 Ma during north-south strike-slip regional deformation. The anisotropy of magnetic susceptibility fabric helps in defining strain localization along narrow north-south to NNE-SSW vertical shear-zones during the exhumation history. Exhumation of the terrane. assessed using U-Pb, Ar-Ar and Rb-Sr methods. was presumably slow with uplift rates around 0.2-0.5 mm/year. Preliminary estimates of contemporaneous horizontal movements suggest that they were one order of magnitude larger. (C) 2002 Elsevier Science B,V, All rights reserved.