Multiple deformation patterns in the Otjosondu manganese mining area, eastern Damara Belt, Namibia

In the southern Central Zone of the western part of the inland branch of the Damara Orogen, early fold phases are difficult to identify because of intense D 2 and D 3 overprinting. In the east, however, at Otjosondu, the D 3 event is much less intense; early fold generations are therefore more easily identified. The D 1 phase of deformation in the study area is accompanied by an appreciable component of simple shear, and a poly harmonic suite of F 1 folds has developed. Recumbent to inclined as well as upright tight and upright open folds have been recognized. The variation in orientation and style of D1 folds and the angle of 40-60° between the D1 and the D2 shortening directions result in contrasting styles of superposed fold patterns between these two generations. The superposition of D 2 folds on recumbent D 1 folds led to the development of dome-crescent mushroom interference patterns. In contrast, depending on the interlimb angle of upright D 1 fold morphologies, these D 1 folds either preserved their original D 1 trend or have been reactivated and reorientated to differing extents by fold hinge migration during D 2 deformation. The orthogonal superposition of D 3 warping on D 2 folds led to distorted dome-and-basin interference fold patterns. Brittle deformation fabrics have been observed as a conjugate set of sinistral and dextral arrays of shear fractures. A set of horizontal stress-release fractures developed predominantly in quartzitic lithologies. D 2 and D 3 folds are correlated with obvious fold patterns developed throughout the Central Zone. The D 1 phase has only been recognized close to the Okahandja Lineament. Elsewhere in the inland branch this reactivation of 01 folds by the D 2 deformation phase may explain why the identification of D 1 folds has been difficult.