Native sulfur at the seafloor: Composition and origin

• Published in: Chemical geology Vol. 668; p. 122295
• Main Authors: Dekov, Vesselin M., Koschinsky, Andrea, Yamanaka, Toshiro, Petersen, Sven, Paul, Sophie A.L., Kleint, Charlotte, Pelleter, Ewan, de Lange, Gert J., Kürzinger, Victoria, Garbe-Schönberg, Dieter, Ilieva, Monika, Fouquet, Yves, Rouxel, Olivier
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 20.11.2024
• Subjects: Alteration; Back-arc rifts; Disproportionation; Mid-ocean ridges; Native S; Synproportionation; Volcanic arcs; Volcanic arcs; Disproportionation; Native S; Alteration; Synproportionation; Back-arc rifts; Mid-ocean ridges
• ISSN: 0009-2541
• DOI: 10.1016/j.chemgeo.2024.122295

Mineralogy, geochemistry and sulfur (S) isotope composition of native sulfur (S0) precipitated at intraoceanic and intracontinental back-arc rift, submarine and subaerial volcanic arc, sediment and sediment-free mid-ocean ridge, hot spot, accretionary wedge, and submarine and continental cave settings were investigated with a main goal to understand the mode of formation of all the types of native S at the modern seafloor. Native S occurs as various depositional forms: chimneys, colloform flows, liquid ponds, slabs; fills in cavities and pore space of the sediment, vesicles and cracks in volcanic rocks; cements and coats the sediment; stains the conduits or fills in pores of the sulfide chimneys; forms fine-grained layers within the sediment; coats the walls, stalactites and stalagmites in the caves. Mineralogically, the native S from the seafloor is pure rhombic S0 with negligible impurities of metal sulfides, aluminosilicates, and carbonates inferred from the chemistry data. Mineral interrelations and S isotope data suggest that native S from different geologic settings has different origin. In the sulfide chimneys and mounds at the mid-ocean ridges, native S appears to be a result of oxidative alteration of primary pyrrhotite. The native S from back-arc rifts, volcanic arcs and hot spots can be a result of either disproportionation of magmatic SO2 (δ34S < 0 ‰), or synproportionation of magmatic SO2 and H2S (δ34S > 0 ‰). The native S from the sediments in anoxic brine-filled deeps (accretionary wedge setting) is a result of bacterial sulfate reduction and consequent sulfide (δ34S < 0 ‰) oxidation. The native S coating the cave walls and forms also has a bacterial origin (δ34S < 0 ‰). •Native S precipitates in a variety of seafloor settings.•Oxidative alteration of pyrrhotite results in S0 formation at the mid-ocean ridges.•S0 forms via disproportionation of SO2 at volcanic arcs, back-arcs and hot spots.•SO2 - H2S synproportionation results in S0 formation at volcanic arcs and back-arcs.•Bacterial sulfate reduction and sulfide oxidation play a role in S0 precipitation.