The Join of the Coastal and Intracontinental Branches of the Damara Orogen, Namibia, South West Africa

Abstract

The Brandberg West area is characterised by N-S trending and west-facing open to isoclinal folds and by a low-grade to very low-grade regional metamorphism. The regional style of deformation indicates a high structural level and, possibly, the presence of a surface of detachment which separated a comparatively thin sedimentary cover (Khomas Subgroup) from underlying less deformable pre-Damara basement rocks.

Both the westerly vergence of the main folding and the low-grade to very low-grade metamorphism of the sediments are in agreement with the assumption of a basement ridge (“Huab Ridge”) extending from the large Kamanjab Inlier towards the southwest. The Huab Ridge separated, during a major part of the Damaran depositional history, the intracratonic from the coastal branch of the orogen. It is thus a major structural feature of the Damara Orogen.

Syn- to late-tectonic granitic intrusions led to extensive post-s1 contact metamorphism which was superimposed on the very low-grade regional metamorphism. K/Ar datings carried out on pelites and subgreywackes on the fraction 2 μm yielded ages of 490 ± 10, 418 ± 10, 422 ± 10, and 431 ± 10 Ma. The age of 490 ± 11 Ma may represent the peak of low-grade regional metamorphism, while the younger ages may correspond to a local rejuvenation caused by late- to post-tectonic granitic intrusions.