Cycling of sulfur in subduction zones: The geochemistry of sulfur in the Mariana Island Arc and back-arc trough

Abstract

The sulfur contents and sulfur isotopic compositions of 24 glassy submarine volcanics from the Mariana Island Arc and back-arc Mariana Trough were determined in order to investigate the hypothesis that subducted seawater sulfur (t~345 = 21%o) is recycled through arc volcanism. Our results for sulfur are similar to those for subaerial arc volcanics: Mariana Arc glasses are enriched in 345 (t~345 = up to 10.3%o, mean = 3.8%o) and depleted in S (20-290 ppm, mean = 100 ppm) relative to MORB (850 ppm S, t~345 = 0.1 "}" 0.5%o). The back-arc trough basalts contain 200-930 ppm S and have 634S values of 1.1 + 0.5%0, which overlap those for the arc and MORB. The low sulfur contents of the arc and some of the trough glasses are attributed to (1) early loss of small amounts of sulfur through separation of immiscible sulfide and (2) later vapor-melt equilibrium control of sulfur contents and loss of sulfur in a vapor phase from sulfide-undersaturated melts near the minimum in sulfur solubility at fO 2-NNO (nickel-nickel oxide). Although these processes removed sulfur from the melts their effects on the sulfur isotopic compositions of the melts were minimal. Positive trends of 6 348 with S7Sr/86Sr, LILE and LREE contents of the arc volcanics are consistent with a metasomatic seawater sulfur component in the depleted sub-arc mantle source. The lack of a 34S-rich slab signature in the trough lavas may be attributed to equilibration of metasomatic fluid with mantle material along the longer pathway from the slab to the source of the trough volcanics. Sulfur is likely to have been transported into the mantle wedge by metasomatic fluid derived from subducted sediments and pore fluids. Gases extracted from vesicles in arc and back-arc samples are predominantly H20 , with minor CO 2 and traces of H2S and SO 2. CO 2 in the arc and back-arc rocks has 613C values of-2.1 to-13.1%o, similar to MORB. These data suggest that degassing of CO 2 could explain the .slightly lower t513C values for some Mariana Trough volcanic glasses, and that incorporation of subduction-derived organic carbon into the Mariana Trough mantle source may not be necessary. More analyses are required to resolve this question, however.

Mineralogical and Geochemical Characteristics of Hydrothermal Minerals Collected from Hydrothermal Vent Fields in the Southern Mariana Spreading Center

“…In contrast, island arc magma has higher δ 34 S values of up to +7 ‰ due to the presence of a subduction-related seawater sulfate component in the subarc mantle source . The δ 34 S values of backarc magma lie between those of MORB and island arc rocks (Alt et al 1993). In the Southern Mariana Trough, the close proximity of arc volcanoes to the spreading center may be responsible for the axial high of the spreading center.…”

Long-term sedimentary recycling of rare sulphur isotope anomalies

“…117,119), which is likely conservative for our purposes, and explore a range of [S] ig values between 10 and 1000 ppm. This range is meant to be inclusive and encompasses measurements of a wide range of extrusive, plutonic, felsic, and mafic igneous rocks [120][121][122][123][124][125][126][127] . Our preferred estimate for the overall average igneous sulphur content (300 ppm; ref.…”

Fluid bubbles in melt inclusions and pillow-rim glasses: high-temperature precursors to hydrothermal fluids?

“…This is evident from the composition of fluid inclusions trapped in phenocrysts (Roedder, 1965;Kamenetsky et al, 1986;Coombs and Roedder, 1994;Sobolev and Nikogosian, 1994;Lowenstern, 1995;Yang and Scott, 1996) and gases in vesicles from quenched glasses (Moore et al, 1977;Moore, 1979;Javoy and Pineau, 1991). In contrast, water may dominate in the fluid phase at subsurface pressures, especially in the case of H 2 O-enriched subduction-related magmas, as observed in arc -backarc glasses (e.g., Garcia et al, 1979;Danyushevsky et al, 1992;Alt et al, 1993), melt inclusions (Sobolev and Naumov, 1985), emanations from arc volcanoes (Hedenquist and Lowenstern, 1994) and comparison of H 2 O contents in glasses and melt inclusions (Sobolev and Chaussidon, 1996). Thus, most basaltic (for an exception, see Gurenko et al, 1988) and all felsic magmas are fluid-saturated during crystallisation, and produce a volatile phase in the form of fluid bubbles (Bottinga and Javoy, 1990).…”

“…(3) Optical and microanalytical studies of fluid inclusions in phenocrysts (Sobolev and Nikogosian, 1994) and mantle minerals (Rovetta and Mathez, 1982;Andersen et al, 1984) and fluid-filled vesicles in quenched submarine glasses (Moore and Calc, 1971;Mathez and Yeats, 1976;Yeats and Mathez, 1976;Moore et al, 1977;Alt et al, 1993) and in lavas (de Hoog and van Bergen, 2000) have revealed crystalline (carbonates, silicates, sulfides and chlorides) and amorphous material present on the crystalfluid or glass -fluid interfaces. In most such studies (Moore et al, 1977;Andersen et al, 1984;Alt et al, 1993;Sobolev and Nikogosian, 1994), the origin of solid phases in fluid bubbles was ascribed to the exchange reactions between the volatile components of trapped fluids (H, C and S) and elements from host minerals or melts.…”

“…In most such studies (Moore et al, 1977;Andersen et al, 1984;Alt et al, 1993;Sobolev and Nikogosian, 1994), the origin of solid phases in fluid bubbles was ascribed to the exchange reactions between the volatile components of trapped fluids (H, C and S) and elements from host minerals or melts. An alternative explanation, namely initially high concentrations of Cu, Na and Cl in magmatic vapor, has followed the discovery of copper sulfides in CO 2 -and Cl-bearing bubbles in phenocryst-hosted melt inclusions (Lowenstern et al, 1991) and salt (halite) crystals in vesicles (Solovova et al, 1991;Lowenstern, 1994a) in the glassy matrix of rhyolites from Pantelleria (Strait of Sicily).…”