Ancient and recycled sulfur sampled by the Iceland mantle plume

• Published in: Earth and Planetary Science Letters
• Main Authors: Ranta, Eemu, Gunnarsson-Robin, Jóhann, Halldórsson, Sæmundur A., Ono, Shuhei, Izon, Gareth, Jackson, Matthew G., Reekie, Callum D.J., Jenner, Frances E., Guðfinnsson, Guðmundur H., Jónsson, Ólafur P., Stefánsson, Andri
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2022
• Subjects: Diablo; Kverkfjöll; Iceland; North Atlantic; Ocean Island
• Online Access: https://oro.open.ac.uk/85082/; https://doi.org/10.1016/j.epsl.2022.117452

Stable sulfur isotope ratios of mid-ocean ridge and ocean island basalts (MORBs and OIBs) preserve unique information about early Earth processes and the long-term volatile cycles between Earth's mantle and the surface. Icelandic basalts present ideal material to examine the oldest known terrestrial mantle reservoir, accessed through a deep-rooted mantle plume, but their multiple sulfur isotope systematics have not been explored previously. Here, we present new sulfur concentration (30–1570 ppm) and isotope data (ẟ 34 S = −2.5 to +3.8‰ and Δ 33 S = −0.045 to +0.016‰; vs. Canyon Diablo Troilite) from a sample suite (n = 62) focused on subglacially erupted basaltic glasses obtained from Iceland's neovolcanic zones. Using these data along with trace element systematics to account for the effects of magmatic processes (degassing and immiscible sulfide melt formation) on ẟ 34 S, we show that primitive (MgO > 6 wt.%), least degassed glasses accurately record the ẟ 34 S signatures of their mantle sources. Compared to the depleted MORB source mantle (DMM; ẟ 34 S = −1.3±0.3‰), the Iceland mantle is shown to have a greater range of ẟ 34 S values between −2.5 and −0.1%. Similarly, Icelandic basalts are characterized by more variable and negatively shifted Δ 33 S values (−0.035 to +0.013‰) relative to DMM (0.004±006‰). Negative low-ẟ 34 S-Δ 33 S signatures are most prominent in basalts from the Snæfellsnes Volcanic Zone and the Kverkfjöll volcanic system, which also have the lowest, most MORB-like 3 He/ 4 He (8–9 R/R A , where R A is the 3 He/ 4 He of air) and the highest Ba/La (up to 12) in Iceland. We propose that subduction fluid-enriched, mantle wedge type material, possibly present in the North Atlantic upper mantle, constitutes a low-ẟ 34 S-Δ 33 S component in the Icelandic mantle. This suggests that volatile heterogeneity in Iceland, and potentially at other OIBs, may originate not only from diverse plume-associated mantle components, but also from a heterogeneous ambient upper mantle. By contrast, a set of ...