Hostname: page-component-cd9895bd7-hc48f Total loading time: 0 Render date: 2024-12-24T01:13:28.085Z Has data issue: false hasContentIssue false
  • English
  • Français

Timing of post–Karoo alkaline volcanism in southern Namibia

Published online by Cambridge University Press:  01 May 2009

D. L. Reid ,
A. F. Cooper ,
D. C. Rex  and
R. E. Harmer
D. L. Reid
Affiliation:
Department of Geochemistry, University of Cape Town, Rondebosch 7700, South Africa
A. F. Cooper
Affiliation:
Department of Geology, University of Otago, Dunedin, New Zealand
D. C. Rex
Affiliation:
Department of Earth Sciences, The University, Leeds, United Kingdom
R. E. Harmer
Affiliation:
Division of Earth, Marine and Atmospheric Sciences, CSIR, Pretoria, Republic of, South Africa
Get access Rights & Permissions [Opens in a new window]

Abstract

New radiometric age data are reported for alkaline centres in southern Namibia, and are discussed together with published age data in terms of models put forward to account for post-Karoo (Mesozoic–Recent) alkaline magmatism within the African plate. Agreement between K–Ar and Rb–Sr ages indicate emplacement of the Dicker Willem carbonatite in southern Namibia at 49 ± 1 Ma. Alkaline rocks associated with the Gross Brukkaros volcano show a discordant radiometric age pattern, but the best estimate for the age of this complex is 77 ± 2 Ma, similar to that obtained for the neighbouring Gibeon carbonatite-kimberlite province. The Dicker Willem carbonatite is therefore younger than the Luderitz alkaline province (133 ± 2 Ma), and the Gross Brukkaros volcano, but is older than the Klinghardt phonolite field (29–37 Ma). The new age data argue against a distinct periodicity in alkaline igneous activity in southern Africa, thereby ruling out possible controls by episodic marginal upwarping of the subcontinent. Although the available age data do not appear to be consistent with the passage of one or even two hotspots under southern Namibia, it is argued that the surface expression of hotspots under continents may be so large and overlapping that within-plate magmatism attributed to these thermal anomalies need not necessarily be confined to narrow linear belts or show an age progression. The role of hotspots in continental alkaline magmatism is most likely one of melt generation, while local crustal structure probably controls the distribution and timing of eruption. Major tectonic boundaries in the Precambrian basement underlying southern Namibia seem to have controlled the development of Tertiary alkaline centres in that region.

Type
Articles
Information
Geological Magazine , Volume 127 , Issue 5 , September 1990 , pp. 427 - 433
Copyright
Copyright © Cambridge University Press 1990

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Allsopp, H. L. & Barrett, D. R. 1975. Rb–Sr age determinations on South African kimberlite pipes. In Physics and Chemistry of the Earth, vol. 9, (ed. Ahrens, L. H., Dawson, J. B., Duncan, A. R. and Erlank, A. J.), pp. 605–17. Oxford: Pergamon Press.CrossRefGoogle Scholar
Blignault, H. J., Jackson, M. P. A., Beukes, G. J. & Toogood, D. J. 1974. The Namaqua tectonic province in South West Africa. Bulletin of the Precambrian Research Unit, University of Cape Town 15, 29–47.Google Scholar
Blignault, H. J., van Aswegen, G., van Der Merwe, S. W. & Colliston, W. P. 1983. The Namaqua geotraverse and environs: part of the Proterozoic mobile belt. Special Publication of the Geological Society of South Africa, no. 10, 1–29.Google Scholar
Briden, J. C., Rex, D. C., Faller, A. M. & Tomblin, J. F. 1979. Geochronology and palaeomagnetism of volcanic rocks in the Lesser Antilles island arc. Philosophical Transactions of the Royal Society of London, B291, 485–528.Google Scholar
Cooper, A. F. 1988. Geology of Dicker Willem, a sub-volcanic carbonatite complex in south-west Namibia. Communications of the Geological Survey of Namibia 4, 3–12.Google Scholar
Dalrymple, G. B. & Lanphere, M. A. 1969. Potassium-Argon Dating. San Francisco: W. H. Freeman, 258 pp.Google Scholar
Duncan, R. A. 1981. Hotspots in the Southern Oceans – An absolute frame of reference for the motions of the Gondwana continents. Tectonophysics 74, 29–42.CrossRefGoogle Scholar
Ferguson, J., Martin, H., Nicolaysen, L. O. & Danchin, R. V. 1975. Gross Brukkaros: A kimberlite–carbonatite volcano. In Physics and Chemistry of the Earth vol. 9, (ed. Ahrens, L. H., Dawson, J. B., Duncan, A. R. and Erlank, A. J.), pp. 219–34. Oxford: Pergamon Press.CrossRefGoogle Scholar
Harmer, R. E. 1985. Rb–Sr isotopic study of units of the Pienaars River alkaline complex, north of Pretoria, South Africa. Transactions of the Geological Society of South Africa 88, 215–23.Google Scholar
Hartnady, C. J. & le Roex, A. P. 1985. Southern Ocean hotspot tracks and the Cenozoic absolute motion of the African, Antarctic, and South American plates. Earth and Planetary Science Letters 75, 245–57.CrossRefGoogle Scholar
Hartnady, C. J., Joubert, P. & Stowe, C. W. 1985. Proterozoic crustal evolution in southwestern Africa. Episodes 8 (4), 236–44.CrossRefGoogle Scholar
Jackson, M. P. A. 1976. High-grade metamorphism and migmatization of the Namaqua Metamorphic Complex around Aus in the southern Namib desert, South West Africa. Bulletin of the Precambrian Research Unit, University of Cape Town 18, 299 pp.Google Scholar
Janse, A. J. A. 1969. Gross Brukkaros, a probable carbonatite volcano in the Nama Plateau of South-Westfrica. Geological Society of America Bulletin 80, 573–86.CrossRefGoogle Scholar
Janse, A. J. A. 1971. Monticellite bearing porphyritic peridotite from Gross Brukkaros, S. W. A. Transactions of the Geological Society of South Africa 74, 45–56.Google Scholar
Kröner, A. 1973. Comments on ‘Is the African plate stationary?’ Nature 243, 29–30.CrossRefGoogle Scholar
Lock, B. E. & Marsh, J. S. 1981. Tertiary phonolite volcanism in the Klinghardt Mountains of South West Africa/Namibia. Transactions of the Geological Society of South Africa 84, 1–6.Google Scholar
Marsh, J. S. 1973. Relationships between transform directions and alkaline igneous rock lineaments in Africa and South America. Earth and Planetary Science Letters 18, 317–23.CrossRefGoogle Scholar
Marsh, J. S. 1975. The Luderitz Alkaline Province, South West Africa I. Descriptive petrology of the Granitberg foyaite complex. Transactions of the Geological Society of South Africa 78, 215–23.Google Scholar
Martin, H., Mathis, M. & Simpson, E. S. W. 1960. The Damaraland subvolcanic ring complexes in South West Africa. Report of the 21st International Geological Congress 13, 156–74.Google Scholar
Mathias, M. 1974. Alkaline rocks of southern Africa. In The Alkaline Rocks (ed. Sorensen, H.), pp. 189–202. London: John Wiley.Google Scholar
Miller, McG. R. & Reimold, W. U. 1986. Excursion guide to the Gross Brukkaros and Roter Kamm craters, South West Africa/Namibia. International Workshop of Cryptoexplosion Structures and Catastrophes in the Geological Record, 87 pp.Google Scholar
Moore, A. E. 1976. Controls of post-Gondwanaland alkaline volcanism in Southern Africa. Earth and Planetary Science Letters 31, 291–6.CrossRefGoogle Scholar
Morgan, J. W. 1983. Hotspot tracks and the early rifting of the Atlantic. Tectonophysics 94, 123–39.CrossRefGoogle Scholar
le Roex, A. P. 1986. Geochemical correlation between southern African kimberlites and South Atlantic hotspots. Nature 324, 243–5.CrossRefGoogle Scholar
Siedner, G. & Miller, J. A. 1968. K–Ar determination on basaltic rocks from South West Africa, and their bearing on continental drift. Earth and Planetary Science Letters 4, 451–8.CrossRefGoogle Scholar
Siedner, G. & Mitchell, J. G. 1976. Episodic Mesozoic volcanism in Namibia and Brazil: A K–Ar isochron study bearing on the opening of the South Atlantic. Earth and Planetary Science Letters 30, 292–302.CrossRefGoogle Scholar
Steiger, R. H. & Jäger, E. 1977. Subcommission on geochronology: convention of the use of decay constants in geo- and cosmochronology. Earth and Planetary Science Letters 36, 359–62.CrossRefGoogle Scholar
White, R. & McKenzie, D. 1989. Magmatism at rift zones: The generation of volcanic continental margins and flood basalts. Journal of Geophysical Research 94, B6, 7685–729.CrossRefGoogle Scholar
York, D. 1969. Least squares fitting of a straight line with correlated errors. Earth and Planetary Science Letters 5, 320–4.CrossRefGoogle Scholar