Major Structural Features and the Tectonic Evolution of the Bossangoa- Bossembele Basement, Northwestern Central African Republic

ABSTRACT

Planar structures (foliations and shear zones) and linear structures (lineations, fold axes) around the Bossangoa and Bossembele area (northwestern part of the Central African Republic) in the North Equatorial fold belt have been investigated and analyzed with the aim of unraveling the major structural elements and the tectonic evolution of the basement. The foliations show two major trends, an older flat-lying granulitic layering of uncertain age reworked by later, Neoproterozoic NE-SW ductile, sinistral shearing and mylonitization. The related lineation is conspicuous and corresponds to a mineral and stretching lineation. It trends N0-30°E with a moderate plunge (0-15) towards the north. F1 folds occur only as decimeter-sized isoclinals folds; their axial traces are roughly parallel to the lineation. The brittle phase characterized by NW-SE-trending open and partially filled fractures is younger than the mylonitization. Quartzofelsdpathic anatectic veins or planes are commonly boudinaged, and the shape of boudins rather suggests non-coaxial deformation. The mylonitic foliation with associated stretching lineation and the ductile shear zone are recognized for the first time and support a tectonic evolution in which ductile deformation was overprinted by brittle failure accompanied by the emplacement of some intrusives.