Near-zero 33S and 36S anomalies in Pitcairn basalts suggest Proterozoic sediments in the EM-1 mantle plume

Volcanic rocks erupted among Pitcairn seamounts sample a mantle plume that exhibits an extreme Enriched Mantle-1 signature. The origin of this peculiar endmember remains contentious, and could involve the recycling marine sediments Archean or Proterozoic ages, delaminated units from lower continental crust, metasomatized peridotites lithospheric mantle. Here, we report sulfur multi-isotopic signature (32S, 33S, 34S, 36S) 15 fresh submarine basaltic glasses three seamounts. We observe evidence for magmatic degassing melts ∼2,000 meters below seawater level (mbsl). Sulfur concentrations are correlated with eruption depth, range between 1300 ppm S (collected ∼ 2,500 mbsl) 600 (∼2,000 mbsl). δ34S values can be accounted under equilibrium isotope fractionation during degassing, αgas-melt 1.0020 1.0001 starting −0.9‰ +0.6‰. estimates similar higher than MORB signatures, suggesting contribution recycled 1‰ 34S enrichment compared to Pacific upper Δ33S Δ36S signatures average at +0.024±0.007‰ +0.02±0.07‰ vs. CDT, respectively (all 1σ). Only is statistically different MORB, by +0.02‰. invariant across sulfide segregation. suggest it reflects source rather high-temperature in basalts. Despite small magnitude 33S-36S variations, our data require substantial amount overwhelm source. show models involving peridotites, crust units, sediments, may viable, but restricted narrow sets circumstances. Instead, scenarios appear most parsimonious explanation EM-1 Pitcairn.