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.

Keywords: sulfur isotopes; HIMU; mantle recycling

Domains: Sciences of the Universe [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, p. 54-71. ⟨10.1029/2020GC009081⟩. ⟨insu-03584471⟩