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Journal of the Geological Society

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U–Pb zircon (SHRIMP) ages for the Lebombo rhyolites, South Africa: refining the duration of Karoo volcanism

^{1 1}British Antarctic Survey, High Cross, Madingley Road, Cambridge, CB3 0ET, UK (e-mail: t.riley@bas.ac.uk)
^{2 2}British Antarctic Survey c/o NERC Isotope Geosciences Laboratory, Keyworth, Nottingham, NG12 5GG, UK
^{3 3}School of Geological and Computer Sciences, University of Natal, Durban 4041, South Africa
^{4 4}PRISE, Research School of Earth Sciences, The Australian National University, Mills Road, Canberra, A.C.T. 0200, Australia

U–Pb SHRIMP ages are reported for three rhyolite flows from the Lebombo rift region of the Karoo volcanic province. Two flows are interbedded with the Sabie River Basalt Formation and a third sample is from the overlying rhyolitic Jozini Formation. The interbedded rhyolites yield ages of 182.0 ± 2.1 and 179.9 ± 1.8 Ma, whilst the overlying Jozini Formation rhyolite yields an age of 182.1 ± 2.9 Ma. Combined with existing ⁴⁰Ar/³⁹Ar geochronology, the new SHRIMP data fine-tunes the chronology of the Karoo volcanic province and indicates the 12 km succession of volcanic rocks in the Lebombo rift were erupted in 1–2 million years and lends considerable support to the links between the Pleinsbachian–Toarcian extinction event and the global environmental impact of Karoo volcanism.

KEYWORDS: Lemombo rhyolites, U–Pb, flood basalts, rhyolites, Karoo

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