Isotopically heavy sulfur in nephelinite from Etinde, Cameroon Volcanic Line

Description

We present a sulfur isotope dataset for lavas from Etinde, a volcano of the Cameroon Volcanic Line. We measured sulfur isotope compositions with an aim to characterise the geochemical reservoir the sulfur came from. We also provide some whole rock geochemical data for context. Major-element compositions were determined by X-Ray Fluorescence (XRF) spectrometry at the University of Edinburgh, and trace element concentrations were determined by Inductively-Coupled Plasma Mass Spectrometry (ICP-MS) at the Scottish Universities Environmental Research Centre (SUERC). Sulfur concentrations were measured using combustion ion-chromatography at Universität Tübingen. Sulfate phases were dissolved in cold HCl at the University of Edinburgh using a method proposed by Renzulli et al., (1998) and solutions were analysed at the stable isotope facility at SUERC. Sulfide samples were prepared and analysed at the University of St Andrews following Canfield et al., 1986. Sulfide δ34S was calculated by mass-balance from measured acid-volatile and chromium-reducible sulfide components. Mass balance was also used to calculate bulk δ34S from sulfide and sulfate δ34S. Bulk δ34S which best represents Etinde magmatic values ranges from +3.7‰ to +6.3‰, a heavier signature than MORB and most other alkaline igneous rocks. We show that the most mafic Etinde samples are highly degassed, a process which affected their S-isotope composition. We suggest that assimilation of evaporite in shallow magma reservoirs or the involvement of a metasomatic carbonate component in the mantle source may explain these positive values.

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