Isotopic Evidence for Multiple Recycled Sulfur Reservoirs in the Mangaia Mantle Plume

J. W. Dottin , J. Labidi (1) , M. G. Jackson , J. Woodhead , J. Farquhar

1 IPGP (UMR_7154) - Institut de Physique du Globe de Paris

Mangaia, an ocean island in the Cook-Austral volcanic chain, is the type locality for the HIMU mantle reservoir and has also been shown to exhibit evidence for recycled sulfur with anomalous δ³⁴S and Δ³³S that has been attributed an Archean origin. Here we report bulk S-isotope data from sulfide inclusions in olivine and pyroxene phenocrysts from one of the previously analyzed and four additional Mangaia basalts to further test for the prevalence of anomalous S in the HIMU mantle source feeding Mangaia. We document compositions that range from -5.13‰ to +0.21‰ (±0.3 2σ), +0.006‰ to +0.049‰ (±0.016 2σ), -0.81‰ to +0.69‰ (±0.3 2σ) for δ³⁴S, Δ³³S, and Δ³⁶S, respectively. These data extend the range of measured compositions and suggest S-isotope heterogeneity in the HIMU mantle source at Mangaia. We show that S-isotope compositions of bulk sulfide in olivine is not in isotopic equilibrium with bulk sulfide in pyroxene from the same samples and that samples from a confined area (M4, M10, M12, and M13) in the northern central part of the island show a distinct covariation for δ³⁴S and Δ³³S. This isotopic variation (forming an array) suggests mixing of sulfur from two sources that were captured at different stages of crystallization by phenocrysts in the Mangaia HIMU sulfur endmember.

Mots clés: sulfur isotopes; HIMU; mantle recycling

Domaines: Planète et Univers [physics]

J. W. Dottin, J. Labidi, M. G. Jackson, J. Woodhead, J. Farquhar. Isotopic Evidence for Multiple Recycled Sulfur Reservoirs in the Mangaia Mantle Plume. Geochemistry, Geophysics, Geosystems, 2020, 21, pp.54-71. ⟨10.1029/2020GC009081⟩. ⟨insu-03584471v2⟩