1887

oa South African Journal of Geology - Synthesis and interpretation of structures along the north-eastern boundary of the Namaqua Tectonic Province, South Africa

Volume 89 Number 2
  • ISSN : 1012-0750
  • E-ISSN: 1996-8590

 

Abstract

Recent structural mapping along the Orange River between Prieska and Upington has shown that the Kheis Subprovince folds (KFl-3) were overprinted by the main (NF2) Namaqua folds. The 1800 Ma-old Kheis Subprovince diverges northwards away from the 1 300 to 1 000 Ma-old Namaqua Province and extends for at least 350km beneath the dune-covered southern Kalahari. Low metamorphic grade quartzites, phyllites, and chloritic amphibolites of the Olifantshoek Sequence were formerly deposited in fluvial to shallow marine settings parallel to the Kaapvaal Craton margin. The sequence was folded and thrust eastwards as a thin-skinned thrust belt and is subdivided into six tectonostratigraphic domains, separated by probable thrust zones with mylonites in some places. Large and small-scale early KFl recumbent folds affected both the Matsap and the overlying Groblershoop formations though the former was deformed mainly by bedding-parallel thrusts. In the west the KF2 folds are also east-vergent and associated with a second set of thrusts. These structures are correlated with the early NFl folds and closure of the Wilgenhoutsdrif volcanic basin in the Namaqua Province. Large, open, north-plunging KF3 folds are confined to discrete zones mainly along the east side of the Skeurberge.

Transition to the Namaqua Province occurs across a 20 to 50km-wide zone, designated the Upington Terrane, and consisting of mainly Kaaien Group quartzites, overprinted by the north-west-trending Namaqua Province NF2 folds and metamorphic zonation. Early thrust domains of the Groblershoop Formation within the Kheis Subprovince, extend westwards into the Upington Terrane, now folded around the NF2 folds, turned up on edge and disrupted along the main Brakbos-Dagbreek-Straussburg shear zone that forms the south-west boundary with the adjacent Kakamas Terrane. The main feature of the Kakamas Terrane is the central axis of high-grade gneiss, granulite, charnockite and late-tectonic granite across which the steeply-dipping, divergent foliation fan was arched (ND4) in a transcurrent shear regime. The north-east boundary with the Upington Terrane is marked by calc-alkaline amphibolites of the Jannelsepan Formation. In the south-west of the Kakamas Terrane the lithologically and structurally different Korannaland Sequence may be part of an accreted microcontinent behind the Jannelsepan "arc". Thrust mechanisms, possible accretion, and obduction of the early precursor Wilgenhoutsdrif volcanic basin, are discussed.

Loading full text...

Full text loading...

Loading

Article metrics loading...

/content/journal/10520/EJC-1bb4cc36db
1986-05-01
2020-09-20

This is a required field
Please enter a valid email address
Approval was a Success
Invalid data
An Error Occurred
Approval was partially successful, following selected items could not be processed due to error