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Overlap of Karoo and Ferrar magma types in KwaZulu-Natal, South Africa

Riley, T.R.; Curtis, M.L.; Leat, P.T.; Watkeys, M.K.; Duncan, R.A.; Millar, I.L.; Owens, W.H.. 2006 Overlap of Karoo and Ferrar magma types in KwaZulu-Natal, South Africa. Journal of Petrology, 47 (3). 541-566. 10.1093/petrology/egi085

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Abstract/Summary

A suite of mafic dykes from the Underberg region of southern KwaZulu-Natal (South Africa) were intruded at 178 Ma, coincident in age with the major Okavango Dyke Swarm of Botswana, and also coincident with minor Karoo-related intrusions of the northern and central Lebombo. The dykes are all low-Ti-Zr tholeiites, they trend NW-SE and are presumed to continue into the Karoo central area of the Lesotho Highlands. In many respects, the Underberg dykes are similar to the majority of the low-Ti-Zr volcanic and subvolcanic intrusions of the Karoo; however, their 87Sr/86Sr and Nd isotope ratios are either ‘Ferrar-like’ (87Sr/86Sr 0·710; Nd < -3) or transitional between Karoo low-Ti-Zr and Ferrar low-Ti magmas. A potential Ferrar source for at least some of the Underberg dykes is supported by anisotropy of magnetic susceptibility analyses of the dyke suite, which demonstrate absolute flow direction from the SE to the NW, consistent with Gondwana reconstructions. The role of crustal contamination and combined fractional crystallization is also demonstrated to have played a key role in the petrogenesis of the Underberg dykes, involving a local upper crust contaminant. However, the composition of the ‘Ferrar-like’ dykes cannot be easily explained by AFC processes, but they do demonstrate that melting of a lithospheric mantle source enriched to a small degree by subduction-derived fluid was also important.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1093/petrology/egi085
Programmes: BGS Programmes > NERC Isotope Geoscience Laboratory
BAS Programmes > Antarctic Science in the Global Context (2000-2005) > Antarctica in the Dynamic Global Plate System
ISSN: 0022-3530
Additional Information. Not used in RCUK Gateway to Research.: Full text not available from this repository
Additional Keywords: Dykes
NORA Subject Terms: Earth Sciences
Date made live: 20 Aug 2007 14:46
URI: http://nora.nerc.ac.uk/id/eprint/107

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