首页|Constraints on the sulfur subduction cycle in Central America from sulfur isotope compositions of volcanic gases
Constraints on the sulfur subduction cycle in Central America from sulfur isotope compositions of volcanic gases
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NSTL
Elsevier
The sulfur cycle at convergent margins remains poorly constrained yet is fundamentally important for understanding the redox state of Earth's reservoirs and the formation of ore deposits. In this study we investigate the sulfur isotope composition of high temperature volcanic gases emitted from the Nicaraguan (average of +4.8 +/- 1.3 parts per thousand) and Costa Rican (average of +2.3 +/- 1.3 parts per thousand) arc segments contributing to emissions from the Southern Central American Volcanic Arc (SCAVA; average of +3.8 +/- 1.7 parts per thousand). Along-arc variations in geochemical tracers at SCAVA are widely accepted to reflect variations in subduction parameters and deep fluid sources and correlations between these parameters and gas S isotope compositions are observed. These correlations suggest that gas emissions are sourced from a mixture of mantle S with delta S-34 similar to 0 parts per thousand and isotopically heavy slab-derived sulfur with delta S-34 >= similar to +8 parts per thousand. We employ Monte Carlo mass balance modeling to constrain S inputs to the subduction zone and relative contributions from mantle and slab to arc sulfur emissions. The models indicate that bulk subduction input in Nicaragua has a S isotope composition of +1.4 +/- 0.5 parts per thousand compared to -0.2 +/- 0.4 parts per thousand in Costa Rica, requiring preferential release of isotopically heavy oxidized S from the slab to explain the relatively high delta S-34 observed in arc outputs. We show that the flux of S from the slab is sufficient to oxidize the entire mantle wedge within the lifetime of the arc, indicating that S is a primary oxidizing agent in subduction zones. Furthermore, the preferential removal of heavy S from the slab requires retention of isotopically light S in the residual slab. Subduction-scale fractionation of S isotopes is fundamentally important in explaining why Earth's bulk surface reservoirs are isotopically positive.
NSTL
Elsevier
