MIDCRUSTAL DETACHMENT AND DOMES IN THE CENTRAL ZONE OF THE DAMARAN OROGEN, NAMIBIA

Mapping of the dome structures in the central zone of the Damaran orog en, Namibia, has shown a profound ductile shear zone, the Khan river d etachment, separating the similar to 1000 Ma granitic basement gneiss from the similar to 550 Ma metamorphosed Damaran metasedimentary cover . This shear zone is a regional scale mid-crustal detachment up to two kilometres thick, with an unknown displacement. Extension lineations are orientated NE-SW along the length of the orogen and parallel to th e axes of tight, contemporaneous, periclinal synclinoria in the Damara n cover and parallel to the long axes of the more open, elongate dome structures in the basement gneisses. Various kinematic indicators show that the hanging wall above the detachment has moved towards the sout h-west under extensional conditions. The domes are thought to be the r esult of combined crustal NW-SE compression and SW-NE extension when t he cover escaped and flowed towards the south-west during the oblique collision of the Kalahari and Congo cratons. Evidence from the margins and the interior of the Damaran orogen, where the basement was thrust onto the cratonic platforms, suggests that the collision was sinistra lly transpressive. The structural elements identified so far could be compared to the North American metamorphic core complex model