Lyell Collection
Journal of the Geological Society
Lyell Centre  |   Lyell Collection  |   Subscriptions   |   Geological Society  |   Email alerts  |   Online bookshop  |   Help

Keywords:
Author:
Advanced search>>
This Article
Right arrow Full Text (PDF)
Right arrow References
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by COX, K. G.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Journal of the Geological Society; 1972; v. 128; issue.4; p. 311-336;
DOI: 10.1144/gsjgs.128.4.0311
© 1972 Geological Society of London

The Karroo Volcanic Cycle

KEITH GORDON COX

The petrogenesis of all the Mesozoic igneous rocks of south-eastern Africa is considered in relation to a single unifying thermotectonic event postulated as initiating the disruption of Gondwanaland. The cycle began with the rise of a body of potassium-rich picrific magma from a depth of at least 500 km. This is the predominating source material for most of the rocks in the northern part of the province (e.g. Rhodesia). Overlying and peripheral to the main magma body a zone of normal (sodic) magma was generated and gave rise to some of the northern rocks and most of the southern rocks (e.g. Karroo dolerites, basalts of Lesotho and Swaziland). Initial eruptive products were locally well fractionated but gave way rapidly to highly primitive picritic lavas representing what is termed the culminatory stage of the cycle. A subsequent stage in which the basalts emitted remained relatively uniform and moderately fractionated over a long period of time is referred to as the 'steady state' phase. A waning stage may be represented by more salic rocks such as the phonolites of Lupata (Mozambique) and the associated plutons of the Chilwa province (Malawi). The Cretaceous kimberlites of Southern Africa may represent the terminal igneous activity of the cycle. Superimposed on the cycle of mantle-derived rocks is a minor cycle of anatexis in the crust which gave rise to most of the acid rocks of the province, particularly the rhyolites of the Lebombo monocline. It is suggested that other provinces such as the Deccan Traps and the Tertiary of Greenland may show patterns of igneous activity which are similar to the Karroo cycle in important respects.




This article has been cited by other articles:


Home page
 J PetrologyHome page
J. A. Miller and C. Harris
Petrogenesis of the Swaziland and Northern Natal Rhyolites of the Lebombo Rifted Volcanic Margin, South East Africa
J. Petrology, 2007; 48: 185 - 218.
[Abstract] [Full Text] [PDF]

Home page
 J PetrologyHome page
M. J. O'HARA
Flood Basalts, Basalt Floods or Topless Bushvelds? Lunar Petrogenesis Revisited
J. Petrology, 2000; 41: 1545 - 1651.
[Abstract] [Full Text] [PDF]

Home page
 J PetrologyHome page
Keith Cox--Bibliography
J. Petrology, 2000; 41: 901 - 903.
[Full Text] [PDF]

Home page
 J PetrologyHome page
P. KRISHNAMURTHY, K. GOPALAN, and J. D. MACDOUGALL
Olivine Compositions in Picrite Basalts and the Deccan Volcanic Cycle
J. Petrology, 2000; 41: 1057 - 1069.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society, London, Special PublicationsHome page
R. S. White
Magmatism during and after continental break-up
Geological Society, London, Special Publications, 1992; 68: 1 - 16.
[Abstract] [PDF]

Home page
 Journal of the Geological SocietyHome page
T. F. D. Nielsen and C. K. Brooks
The E Greenland rifted continental margin: an examination of the coastal flexure
Journal of the Geological Society, 1981; 138: 559 - 568.
[Abstract] [PDF]