Title:

The Hakos-Rostock Nappe Complex: a case study of alpine-type thrust tectonics within the Southern Margin Zone of the Damara Orogen, Namibia

Author(s):
Publication Year:
2016
Abstract:

The Southern Margin Zone (SMZ) of the Pan-African Damara Orogen in Namibia constitutes an alpinotype fold and thrust belt in which Neoproterozoic Damara rocks and the Meso- to Palaeozoic basement were tectonically stacked by the collision of the Kalahari and Congo cratons. The Hakos recumbent fold, with more than 100 km of hinge line, is the most spectacular structure of the SMZ; it forms part of a nappe pile that can be subdivided into the lower parautochthonous to allochthonous Rostock Nappe Complex (RNC) and the upper, allochthonous Hakos Nappe Complex (HNC). Detached Basement and Damara rocks are stacked in the basal RNC whereas the HNC is composed of Neoproterozoic passive margin sediments previously subdivided into the older Kudis and younger Vaalgras Subgroups of the Swakop Group. However, structural analysis and geological mapping demonstrate the presence of large scale of thrusts that delimit individual units. Therefore, due to the absence of absolute time markers the current stratigraphic models remain poorly constrained. Three stages of deformation D1-D3 have been identified and are attributed to regional change in transport direction and tectonic style. A predominant shallow-dipping, bedding-parallel S0X-foliation developed under amphibolite facies metamorphism of Barrovian type but may be diachronous in time. In the basal nappes it is related to D1 and carries a sub horizontal NE-SW stretching lineation L1. Overall top-to-the-NE-directed transport with a marked right-lateral component is suggested by asymmetric pressure shadows around L1 stretched clasts and sc-fabrics in granitic orthogneiss. D2 marks a drastic change in transport direction towards the SE. Large-scale folds evolved together with shallow NW dipping thrusts. Three phases of D2-folding vary from early isoclinal through tight to late open folds and are related to the development of distinct regional and local schistosities S2,1 to S2,3 which generally obscure older S-fabrics. A NE plunging stretching lineation is usually developed parallel to the fold axis. SE-directed D2- thrusting occurs all over the study area but is focused at the contacts between individual nappes with displacement attaining crustal-scale. Here, stretching lineations and fold axes turn into a NW-plunging down-dip orientation. Late-stage east-west compression D3 resulted in the local development of strike slip cleavage and gentle folding around N-S trending axes resulting in dome and basin interference structures that are visible at the scale of the geological map. At the orogenic scale the D1 event records NE-directed oblique thrusting of the Congo Craton over the Kalahari Craton. The first phase of nappe emplacement which took place under a right-lateral transpression regime, however, is largely obscured by subsequent deformation. The change in D2 transport towards the southeast is attributed to progressive shortening (or blocking of the D1 thrust zones) leading to the escape of rocks towards the SE, perpendicular to D1. Complementary movements are recorded in the Gariep Belt and suggest overall movement of the Kalahari Craton towards the west; the plate motion post-dates the main phase of tectonometamorphism in the Kaoko Belt that resulted from collision of the Congo Craton with the South American one. It is therefore assumed that the Kalahari Craton remained as an independent plate before the Pan-African Damara event, separated by a wide ocean from both the Congo and South American cratons. Keywords: Kalahari, Damara Orogen, Southern Margin Zone, Nappe Complex, Stratigraphy.

Publication Title:

Communications of the Geological Survey of Namibia

Publisher:
Geological Survey of Namibia
Volume:
17
Pages:
17-50
Item Type:
Journal Article
Language:
en
Keywords:
Files:
Attachment Size
The Hakos_Rostock Nappe Complex.pdf 2.8 MB

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