Constrictional deformation in the Central Zone of the Damara orogen, Namibia

Mid-crustal structures in the axial zone of the Pan-African Damaran orogenic belt show that basement orthogneiss has formed amoeboid elongate domes on the scale of tens of kilometres with overturned non-planar non-cylindrical geometries. These are surrounded by open to tight synclinal envelopes of covering meta-sediments that converge at depressions between the domes. The basement and cover are detached along a regional ductile shear zone. S-L tectonites in the cover and detachment shear zone become strongly rodded L-tectonites in the tighter cores of the basement domes. The mineral lineation and rodding consistently plunges moderately towards the east-northeast. Strain analysis of deformed meta-conglomerates and porphyroblasts demonstrates that these structures formed in a moderately plunging constrictional field. Dome formation and S-L and L-tectonites are interpreted as being the result of a single ductile flow episode within laterally constricted middle crust. This occurred when the Kalahari, Rio del Plata and Congo Cratons collided in latest Neoproterozoic/Cambrian times and forced the Central Zone to extrude and escape out towards the west-southwest. (C) 2002 Elsevier Science Limited. All rights reserved.