Remnants of an Archean oceanic plateau, Belingwe greenstone belt, Zimbabwe

Abstract

Stratigraphic and structural data from the Archean Zimbabwe craton suggest that a major detachment surface exists within the Belingwe greenstone belt. The surface separates ultramafic and mafic magmatic rocks of the upper greenstones in the hanging wall from an ancient gneiss complex, older volcanic-sedimentary rocks, and a shallow-water sedimentary sequence in the footwall. Rocks dated at ca. 2.7 Ga above the detachment surface form the proposed Mberengwa allochthon. The regionally extensive upper greenstone succession represents tectonically emplaced allochthonous sheets, not indigenous magmas erupted within autochthonous continental rifts. Magmatic rocks of the Mberengwa allochthon resemble oceanic plateaus preserved in younger mountain belts. Comparison of the Zimbabwe craton with the Proterozoic Birrimian terranes of west Africa leads us to suggest that Precambrian continental growth may have been characterized by intense structural imbrication related to the difficulty of subduction of buoyant oceanic lithosphere.