Stable isotope study of the Archaean rocks of the Vredefort impact structure, central Kaapvaal Craton, South Africa

Fagereng, Åke; Harris, Chris; Grange, Mandy La; Stevens, Gary

doi:10.1007/s00410-007-0224-6

Cited by 26 publications

(16 citation statements)

References 69 publications

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“…Venneman and Smith 1990;Fagereng et al 2008). Individual clinopyroxenes were analysed by laser fluorination employing BrF 5 as the reagent and measured on O 2 gas (Harris and Vogeli 2010).…”

Section: Methodsmentioning

confidence: 99%

Magmatic evolution of the Cadamosto Seamount, Cape Verde: beyond the spatial extent of EM1

Barker

Troll

Ellam

et al. 2011

Contrib Mineral Petrol

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The Cadamosto Seamount is an unusual volcanic centre from Cape Verde, characterised by dominantly evolved volcanics, in contrast to the typically mafic volcanic centres at Cape Verde that exhibit only minor volumes of evolved volcanics. The magmatic evolution of Cadamosto Seamount is investigated to quantify the role of magma-crust interaction and thus provide a perspective on evolved end-member volcanism of Cape Verde. The preservation of mantle source signatures by Nd-Pb isotopes despite extensive magmatic differentiation provides new insights into the spatial distribution of mantle heterogeneity in the Cape Verde archipelago. Magmatic differentiation from nephelinite to phonolite involves fractional crystallisation of clinopyroxene, titanite, apatite, biotite and feldspathoids, with extensive feldspathoid accumulation being recorded in some evolved samples. Clinopyroxene crystallisation pressures of 0.38-0.17 GPa for the nephelinites constrain this extensive fractional crystallisation to the oceanic lithosphere, where no crustal assimilants or rafts of subcontinental lithospheric mantle are available. In turn, magma-crust interaction has influenced the Sr, O and S isotopes of the groundmass and late crystallising feldspathoids, which formed at shallow crustal depths reflecting the availability of oceanic sediments and anhydrite precipitated in the ocean crust. The Nd-Pb isotopes have not been affected by these processes of magmacrust interaction and hence preserve the mantle source signature. The Cadamosto Seamount samples have high 206 Pb/ 204 Pb ([19.5), high eNd (?6 to ?7) and negative D8/ 4Pb, showing affinity with the northern Cape Verde islands as opposed to the adjacent southern islands. Hence, the Cadamosto Seamount in the west is located spatially beyond the EM1-like component found further east. This heterogeneity is not encountered in the oceanic lithosphere beneath the Cadamosto Seamount despite greater extents of fractional crystallisation at oceanic lithospheric depths than the islands of Fogo and Santiago. Our data provide new evidence for the complex geometry of the chemically zoned Cape Verde mantle source.

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Section: Methodsmentioning

confidence: 99%

Magmatic evolution of the Cadamosto Seamount, Cape Verde: beyond the spatial extent of EM1

Barker

Troll

Ellam

et al. 2011

Contrib Mineral Petrol

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“…Archaean basement rocks exposed in the core of the Vredefort structure and a δ 18 O profile through an 11-km section shows comparatively little variation in whole-rock δ 18 O value, with the majority of wholerock δ 18 O values being between 8 and 10 ‰. The average δ 18 O value of the Vredefort orthogneiss is 9.15 ‰ (2σ = 1.96 ‰, n = 35, Fagereng et al 2008). The oxygen isotope composition of amphibolite to granulite facies pelitic rocks of the Southern Marginal Zone of the Limpopo Belt (Vennemann and Smith 1992) is very similar to those of Vredefort.…”

Section: Crust Versus Mantle Origin Of High δ 18 O Valuesmentioning

confidence: 96%

“…Archaean crust is likely to have lower δ 18 O values; a section through such rocks exposed by the Vredefort impact structure in South Africa (Fig. 1) gives an average δ 18 O value of 9.2 ‰ (Fagereng et al 2008). Using simple mixing models, the amount of contamination required to produce the 1.04 ‰ range in Etendeka picrite magma δ 18 O values is 12 % (schist), 21 % (Spitzkoppe) and 29 % (Vredefort), with errors associated with analytical uncertainty of about 18 % relative.…”

Section: Crust Versus Mantle Origin Of High δ 18 O Valuesmentioning

confidence: 97%

“…Hildreth and Moorbath 1988), potential candidates for lower to middle crust beneath Tuli include the southern marginal zone of the Limpopo metamorphic belt 150 km to the south, and the Vredefort impact structure (Hart et al 1990;Lana et al 2003) which is about 550 km to the south of Tuli. In both cases, an extensive O isotope database is available (Vennemann and Smith 1992;Fagereng et al 2008). Archaean basement rocks exposed in the core of the Vredefort structure and a δ 18 O profile through an 11-km section shows comparatively little variation in whole-rock δ 18 O value, with the majority of wholerock δ 18 O values being between 8 and 10 ‰.…”

Section: Crust Versus Mantle Origin Of High δ 18 O Valuesmentioning

confidence: 99%

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The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

Harris

Roux

Cochrane

et al. 2015

Contrib Mineral Petrol

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Explanations for the high δ 18 O values in Tuli/Mwenezi picrites are limited to (1) alteration, (2) crustal contamination, and (3) derivation from mantle with an abnormally high δ 18 O. Previously, a variety of models that range from crustal contamination to derivation from the 'enriched' mantle lithosphere have been suggested to explain high concentrations of incompatible elements such as K, and average εNd and εSr values of −8 and +16 in Mwenezi (Nuanetsi) picrites. However, the primitive character of the magmas (Mg# 73), combined with the lack of correlation between δ 18 O values and radiogenic isotopic compositions, MgO content, or Mg# is inconsistent with crustal contamination. Thus, an 18 O-enriched mantle source having high incompatible trace element concentration and enriched radiogenic isotope composition is indicated. High δ 18 O values are accompanied by negative Nb and Ta anomalies, consistent with the involvement of the mantle lithosphere, whereas the high δ 18 O themselves are consistent with an eclogitic source. Magma δ 18 O values about 1 ‰ higher than expected for mantle-derived magma are also a feature of the Bushveld mafic and ultramafic magmas, and the possibility exists that a long-lived 18 O-enriched mantle source has existed beneath southern Africa. A mixed eclogite peridotite source could have developed by emplacement of oceanic lithosphere into the cratonic keel during Archaean subduction.

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“…The CRG, dominated by quartzites and gold and uranium bearing conglomerates with a minor shale component, was deposited in a fluvial environment in a retroarc foreland some time after 2902 ± 13 Ma, i.e. the age of the youngest detritital zircon found at the base of the CRG (Kositcin and Krapez, 2004 Fagereng et al, 2008) (1) Vredefort Dome (2) Johannesburg Dome (c) stratigraphic column of the Basin and overlying formations (modified after Frimmel and Minter, 2002). feeder dykes are encountered throughout the basin.…”

Section: Geological Settingmentioning

confidence: 99%

Stable Isotope Composition of Quartz-Calcite Veins in the Witwatersrand Basin, South Africa: Implication for Basin-Scale Fluid Circulation

Jaguin

Boulvais

Poujol

et al. 2010

South African Journal of Geology

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Stable isotope study of the Archaean rocks of the Vredefort impact structure, central Kaapvaal Craton, South Africa

Cited by 26 publications

References 69 publications

Magmatic evolution of the Cadamosto Seamount, Cape Verde: beyond the spatial extent of EM1

Magmatic evolution of the Cadamosto Seamount, Cape Verde: beyond the spatial extent of EM1

The oxygen isotope composition of Karoo and Etendeka picrites: High δ18O mantle or crustal contamination?

Stable Isotope Composition of Quartz-Calcite Veins in the Witwatersrand Basin, South Africa: Implication for Basin-Scale Fluid Circulation

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