THE GARIEP BELT - STRATIGRAPHIC-STRUCTURAL EVIDENCE FOR OBLIQUELY TRANSFORMED GRABENS AND BACK-FOLDED THRUST STACKS IN A COMBINED THICK-SKIN THIN-SKIN STRUCTURAL SETTING
Iw. Halbich et Dj. Alchin, THE GARIEP BELT - STRATIGRAPHIC-STRUCTURAL EVIDENCE FOR OBLIQUELY TRANSFORMED GRABENS AND BACK-FOLDED THRUST STACKS IN A COMBINED THICK-SKIN THIN-SKIN STRUCTURAL SETTING, Journal of African earth sciences, and the Middle East, 21(1), 1995, pp. 9-33
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.