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Three episodes of crustal development in the Rehoboth Province, Namibia

By
Valby Van Schijndel
Valby Van Schijndel
Department of Earth Sciences, University of Gothenburg, SE-40530, Sweden
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David H. Cornell
David H. Cornell
Department of Earth Sciences, University of Gothenburg, SE-40530, Sweden
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K.-H. Hoffmann
K.-H. Hoffmann
Geological Survey of Namibia, 1 Aviation Road, Private Bag 13297, Windhoek, Namibia
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Dirk Frei
Dirk Frei
Department of Earth Sciences, Stellenbosch University, Private Bag X1, 7602 Matieland, South Africa
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Published:
January 01, 2011

Abstract

The African continental crust was assembled by a series of orogenies over a period of billions of years mainly in Precambrian times. Tracing the build-up history of this stable crust is not always straightforward due to multiphase deformation and regions with poor outcrop. Episodes of metamorphism and magmatism associated with multiple Wilson cycles are recorded in zircons, which found their way into sediments derived from the hinterland. Dating of zircon populations in detrital rocks can hence provide age spectra which reflect the metamorphic and magmatic events of the region. Microbeam dating of detrital zircon is used to characterize the crustal development history of the Rehoboth Province of southern Africa. We investigated a quartzite of the Late Palaeo-Early Mesoproterozoic Billstein Formation, formed in a continental basin, and a quartz-feldspar arenite layer of the late Mesoproterozoic Langberg Formation conglomerates, immature sediments formed within a felsic volcanic system (both close to Rehoboth Town). The combined data indicate three episodes of crustal evolution in the Rehoboth Province. The oldest phase is only documented in the Billstein quartzite by three 2.98–2.7 Ga Archaean zircons. A Palaeoproterozoic phase between 2.2 and 1.9 Ga is older than any known exposures of the Rehoboth Province. The Billstein quartzite shows a main peak at 1.87 Ga, corresponding to the 1863±10 Ma Elim Formation. The Langberg sample reflects magmatism related to the entire Namaqua–Natal Wilson cycle between c. 1.32 and 1.05 Ga. The absence of zircons of that age range in the Billstein quartzite indicates a pre-Namaqua age for the Billstein Formation. Our data shows that there were at least three episodes of crustal development at 2.98–2.7 Ga, 2.05–1.75 and 1.32–1.1 Ga. We have documented the existence of a previously unrecognized 2.98–2.7 Ga Archaean crustal component, which was probably exposed in the Rehoboth Province during the Palaeoproterozoic and thus indicates a much longer geological history for the Rehoboth Province than previously known.

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Contents

Geological Society, London, Special Publications

The Formation and Evolution of Africa: A Synopsis of 3.8 Ga of Earth History

D. J. J. Van Hinsbergen
D. J. J. Van Hinsbergen
University of Oslo, Norway
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S. J. H. Buiter
S. J. H. Buiter
Geological Survey of Norway
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T. H. Torsvik
T. H. Torsvik
University of Oslo
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C. Gaina
C. Gaina
Geological Survey of Norway
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S. J. Webb
S. J. Webb
University of the Witwatersrand, South Africa
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Geological Society of London
Volume
357
ISBN electronic:
9781862396050
Publication date:
January 01, 2011

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