Title:
Forearc basin evolution in the Pan-African Damara Belt, central Namibia: the Hureb formation of the Khomas zone
Author(s):
Publication Year:
1992
Abstract:
The Hureb Formation in central Namibia is one of the uppermost stratigraphic units of the Precambrian Pan-African Damara Sequence. The Hureb Formation occurs only in a part of the Khomas Zone, a forearc basin which evolved complexly with time. The formation is composed of the well-graded, upward-fining schists of the quartzitic Keises Member, the graphitic and calcitic Waterval Member and the altered, scapolite-bearing Dagbreek Member. These units accumulated in an elongate turbidite fan system, longitudinally deposited on the northern slopes of a wide forearc basin. The active continental margin initiated when the Kalahari plate subducted oceanic crust underneath the passive continental margin of the Congo craton. The development and deposition of the turbiditic Hureb Formation in the foredeep occurred during subduction of oceanic crust simultaneous with D1 deformation and tholeiitic to andesitic arc volcanism on the continental margin. The basin was bound to the north by the rising, volcanically active continental-margin and to the south by the accretionary prism of obducted slivers of oceanic crust and pelagic sediments above the subduction zone. With continental collision the sedimentation in the forearc and continental margin arc volcanism ceased. The forearc basin was uplifted and shortened horizontally by synclinoria and anticlinoria, which propagated northwards and died out at the edge of the forearc basin. The deformation slightly affected the underlying, foliated Fahlwater schist from the passive margin setting. Further uplift of the basin and re-adjustment between the oblique-sutured cratons (simultaneous with the D3 doming in the Congo continental-margin arc) occurred with the underplating of the thin passive margin of the Kalahari craton. As no more crustal shortening could be absorbed by the upright folding (Dk1, reactivation of the thrusts in the accretionary prism leads to the producing of southeast verging, with a right-lateral sense of movement, thrusts (Dk2) in the folded forearc basin. The Dk2 thrusts propagated and died out northwards and extended towards the south. The stacking of the Dk2 thrusts southwards thickened the crust creating a low heatflow environment with higher pressure conditions. It leads to the preservation of chlorite and production of sillimanite, garnet, staurolite and kyanite. To the south of the accretionary prism, collision related deformation created a peripheral foreland thrust zone outlasting orogenic activities in the overriding Congo continental margin where isostatic rebound already had occurred.
Publication Title:
Precambrian Research
Volume:
57
Issue:
3-4
Pages:
169-194
Item Type:
Journal Article
Language:
en

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