High Sulfur in Primitive Arc Magmas, Its Origin and Implications

Abstract

Sulfur contents in 98.5% of melt inclusions (MI) from calc-alkaline subduction basalts do not exceed 4000 ppm, whereas experimentally established limits of sulfur solubility in basaltic melts with high fO2 (characteristic of subduction zones, e.g., QFM + 2) surpass 14,000 ppm. Here we show that primitive (Mg# 62-64) subduction melts may contain high sulfur, approaching the experimental limit of sulfur solubility. Up to 11,700 ppm S was measured in olivine-hosted MI from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. These MI often contain magmatic sulfide globules (occasionally enriched in Cu, Ni, and platinum-group elements) and anhydrite enclosed within a brown, oxidized glass. We conclude that the ubiquitous low sulfur contents in MI may originate either from insufficient availability of sulfur in the magma generation zone or early magma degassing prior to inclusion entrapment. Our findings extend the measured range of sulfur concentrations in primitive calc-alkaline basaltic melts and demonstrate that no fundamental limit of 4000 ppm S exists for relatively oxidized subduction basalts, where the maximum sulfur content may approach the solubility limit determined by crystallization of magmatic anhydrite.

Sulfur‐rich mafic magma injection into the felsic magma chamber beneath Asama volcano, central Japan: Records in olivine‐hosted melt inclusions from the Itabana and Tenmei eruptions

“…Wallace and Edmonds (2011) explained that more oxidized melts could coexist with anhydrite and ~1.5 wt% dissolved S under oxidizing conditions. Recently, sulfur‐rich melt inclusions and sulfide and sulfate minerals captured by olivine phenocrysts in basaltic scoria have been studied in the arc calc‐alkaline Tolbachik volcano, Kamchatka (Kamenetsky et al, 2018; Zelenski et al, 2018, 2021). Zelenski et al (2021) also found olivine‐hosted melt inclusions with sulfur concentrations as high as 11 700 ppm from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka.…”

“…Recently, sulfur‐rich melt inclusions and sulfide and sulfate minerals captured by olivine phenocrysts in basaltic scoria have been studied in the arc calc‐alkaline Tolbachik volcano, Kamchatka (Kamenetsky et al, 2018; Zelenski et al, 2018, 2021). Zelenski et al (2021) also found olivine‐hosted melt inclusions with sulfur concentrations as high as 11 700 ppm from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. They presented a more extensive dataset collected for melt inclusions from arc volcanoes such as Tolbachik and other examples worldwide, showing that most arc volcanoes remain below 4000 ppm and that the Tolbachik melt inclusions also cluster within the ranges of 1000–3800 ppm sulfur.…”

“…Zelenski et al (2021) also found olivine-hosted melt inclusions with sulfur concentrations as high as 11 700 ppm from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. They presented a more extensive dataset collected for melt inclusions from arc volcanoes such as Tolbachik and other examples worldwide, showing that most arc volcanoes remain below 4000 ppm and that the Tolbachik melt inclusions also cluster within the ranges of 1000-3800 ppm sulfur.…”

“…Recently, sulfur-rich melt inclusions and sulfide and sulfate minerals captured by olivine phenocrysts in basaltic scoria have been studied in the arc calc-alkaline Tolbachik volcano, Kamchatka (Kamenetsky et al, 2018;Zelenski et al, 2018Zelenski et al, , 2021. Mafic melt inclusions of Asama volcano show high sulfur concentrations compared to values reported from other arc volcanoes (Wallace & Edmonds, 2011;Zelenski et al, 2021).…”

“…Sulfur concentration in typical mafic melt inclusions of most arc volcanoes are within 4000 ppm (Zelenski et al, 2021). The ubiquitous limit of sulfur content in the melt inclusions may be attributed to insufficient sulfur availability in the magma generation zone or early magma degassing before inclusion entrapment (Zelenski et al, 2021). Anhydrite has never been found in the erupted materials from the Asama volcano.…”