Tectonic evolution of the Yaoundé segment of the Neoproterozoic Central African Orogenic Belt in southern Cameroon

Abstract

The deformation history of the Neoproterozoic Central African Orogenic Belt in southern Cameroon is well recorded in the low- to high-grade rocks outcropping in the area around Yaoundé. The fabrics in these rocks are consistent with two main ductile deformation events D ₁ and D ₂. D ₁ predated emplacement of calc-alkaline dioritic bodies and caused the formation of nappes that resulted in high-pressure granulite metamorphism of soft sediments. A strong overprinting of these nappes during D ₂ symmetric extension, probably associated with large-scale foliation boudinage and (or) gneissic doming and intense magmatic underplating, gave rise to regional flat-lying fabrics. The latter were further buckled by D ₃ and D ₄ folding phases defining a vertical constriction occurring with a major east–west to NW–SE shortening direction. The corresponding F ₃ and F ₄ folds trend north–south to NE–SW and east–west to NW–SE, respectively, and represent the main regional strain patterns. Based on the east–west to NW–SE maximum shortening orientation indicated by F ₃ folds, it is proposed that the nappe-stacking phase D ₁ occurred in the same direction. The deformation history in the area can thus be described as corresponding principally to alternating east–west to NW–SE contractions and north–south to NE–SW orogenic-parallel extensions. At the regional scale, this could be due to the Transaharan east–west collisional system.