Structural and metamorphic evolution of a gneiss terrain in the Namaqua Belt near Onseepkans, South West Africa
Doctoral Thesis
1976
Permanent link to this Item
Authors
Supervisors
Journal Title
Link to Journal
Journal ISSN
Volume Title
Publisher
Publisher
University of Cape Town
Department
Faculty
License
Series
Abstract
A 4000 km² area of Precambrian rocks in the Namaqua belt has been examined and it is concluded the present structural and metamorphic framework is the result of a complex polydeformational and polymetamorphic evolution. A major crustal break is present in the area and is represented by a northwest trending dextral shear zone - the Pofadder ZAHNCAFS. The zone of reorientation associated with this shear zone controls the geometry of the western part of the area. The shear zone varies in width from 20 to 40 km and the core contains a 2 km - 7 km wide belt of mylonites. Two sets of folds (D₅ and D₆) have been formed in the zone of reorientation in the northern block. The D₅ folds are northeast trending en-echelon structures up to 30 km long and the interference pattern produced by superimposed northwest trending D₆ folds has resulted in a series of crescent-shaped antiforms. These folds are not present in the southern block and this is thought to be due to a pressure shadow effect connected with the nearby Vioolsdrif complex. Components of both pure shear and simple shear were involved in the shear zone development and a minimum displacement of 85 km is indicated by the strain analysis. The shear zone developed under medium to high-grade metamorphic conditions and the mylonites were formed by a process of dislocation and recovery.
Description
Bibliography: p. 173-189.
Keywords
Reference:
Toogood, D. 1976. Structural and metamorphic evolution of a gneiss terrain in the Namaqua Belt near Onseepkans, South West Africa. University of Cape Town.