The Gariep belt: stratigraphic-structural evidence for obliquely transformed grabens and back-folded thrust stacks in a combined thick-skin thin-skin structural setting
This paper deals with the tectonics of the Port Nolloth Zone (PNZ) of the Gariep belt, one of the Pan-African tectono-metamorphic belts along the southwest coast of Africa. Stratigraphical and sedimentological evidence indicates that deposition in the sub-basins was controlled by step and/or graben faults parallel to the craton edge. Some of these structures were inverted during the compressional phase to form oblique wrenches in a subzone proximal to the craton edge, whereas others developed into stacked thrusts, blind ramps and a refolded duplex in a distal subzone. A near vertical ZX plane of deformation strikes north-northwest to south-southeast for the entire PNZ and the shear planes are near horizontal in the distal subzone and near vertical in the proximal area. Because metamorphic grades are very similar everywhere, the difference in style is probably related to the original shape of the basement and the varying lithology of the Gariep rocks. Two-dimensional modelling shows that oblique obduction of an oceanic crustal slab to the southeast, followed by relaxation and renewed compression in three pulses, probably produced a combination of thick-skin and thin-skin elements in a zoned tectonite. © 1995.