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Overlap of Karoo and Ferrar Magma Types in KwaZulu-Natal, South Africa |
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| Authors: | RILEY T R; CURTIS M L; LEAT P T; WATKEYS M K; DUNCAN R A; MILLAR I L; OWENS W H |
| Institution: | 1 BRITISH ANTARCTIC SURVEY, HIGH CROSS, MADINGLEY ROAD, CAMBRIDGE, CB3 0ET, UK 2 SCHOOL OF GEOLOGICAL AND COMPUTER SCIENCES, UNIVERSITY OF KWAZULU-NATAL, DURBAN 4041, SOUTH AFRICA 3 COLLEGE OF OCEANIC AND ATMOSPHERIC SCIENCES, OREGON STATE UNIVERSITY, CORVALLIS, OR 97331-5503, USA 4 BRITISH ANTARCTIC SURVEY, c/o NERC ISOTOPE GEOSCIENCES LABORATORY, KEYWORTH, NOTTINGHAM NG12 5GG, UK 5 SCHOOL OF GEOGRAPHY, EARTH AND ENVIRONMENTAL SCIENCES, UNIVERSITY OF BIRMINGHAM, BIRMINGHAM B15 2TT, UK |
| Abstract: | A suite of mafic dykes from the Underberg region of southernKwaZulu-Natal (South Africa) were intruded at  178 Ma, coincidentin age with the major Okavango Dyke Swarm of Botswana, and alsocoincident with minor Karoo-related intrusions of the northernand central Lebombo. The dykes are all low-Ti–Zr tholeiites,they trend NW–SE and are presumed to continue into theKaroo central area of the Lesotho Highlands. In many respects,the Underberg dykes are similar to the majority of the low-Ti–Zrvolcanic and subvolcanic intrusions of the Karoo; however, their87Sr/86Sr and  Nd isotope ratios are either ‘Ferrar-like’(87Sr/86Sr 0·710; Nd < –3) or transitional betweenKaroo low-Ti–Zr and Ferrar low-Ti magmas. A potentialFerrar source for at least some of the Underberg dykes is supportedby anisotropy of magnetic susceptibility analyses of the dykesuite, which demonstrate absolute flow direction from the SEto the NW, consistent with Gondwana reconstructions. The roleof crustal contamination and combined fractional crystallizationis also demonstrated to have played a key role in the petrogenesisof the Underberg dykes, involving a local upper crust contaminant.However, the composition of the ‘Ferrar-like’ dykescannot be easily explained by AFC processes, but they do demonstratethat melting of a lithospheric mantle source enriched to a smalldegree by subduction-derived fluid was also important. KEY WORDS: dyke; basalt; crustal contamination; large igneous province |
| Keywords: | : dyke basalt crustal contamination large igneous province |
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