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 payer deals with the tectonics of the Port Nolloth Zone (PNZ) of the Gariep belt, one of the Pan-African tectono-metamorphic belts alon g 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 obliqu e wrenches in a subzone proximal to the craton edge, whereas others de veloped into stacked thrusts, blind ramps and a refolded duplex in a d istal subzone. A near vertical ZX plane of deformation strikes north-n orthwest to south-southeast for the entire PNZ and the shear planes ar e near horizontal in the distal subzone and near vertical in the proxi mal area. Because metamorphic grades are very similar everywhere, the difference in style is probably related to the original shape of the b asement 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 e lements in a zoned tectonite.