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Co-variability of S6+, S4+, and S2- in apatite as a function of oxidation state; implications for a new oxybarometer

Konecke, Brian A ; Fiege, Adrian ; Simon, Adam C ; Parat, Fleurice ; Stechern, André

The American mineralogist, 2017-03, Vol.102 (3), p.548-557 [Periódico revisado por pares]

Washington: Mineralogical Society of America

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  • Título:
    Co-variability of S6+, S4+, and S2- in apatite as a function of oxidation state; implications for a new oxybarometer
  • Autor: Konecke, Brian A ; Fiege, Adrian ; Simon, Adam C ; Parat, Fleurice ; Stechern, André
  • Assuntos: Apatite ; apatite crystallization experiments ; buffers ; Carmen Mine ; Chile ; crystal chemistry ; Crystallization ; Durango Mexico ; Earth Sciences ; electron probe data ; experimental studies ; fayalite ; framework silicates ; fugacity ; Geochemistry ; Mexico ; Mineralogy ; nesosilicates ; nonsilicates ; olivine group ; orthosilicates ; Oxidation ; oxybarometer ; phosphates ; quartz ; Sciences of the Universe ; silica minerals ; silicates ; South America ; spectra ; Sulfur ; sulfur oxidation state ; valency ; variations ; X-ray spectra ; XANES ; XANES spectra
  • É parte de: The American mineralogist, 2017-03, Vol.102 (3), p.548-557
  • Descrição: In this study, we use micro-X-ray absorption near-edge structures (µ-XANES) spectroscopy at the S K-edge to investigate the oxidation state of S in natural magmatic-hydrothermal apatite (Durango, Mexico, and Mina Carmen, Chile) and experimental apatites crystallized from volatile-saturated lamproitic melts at 1000 °C and 300 MPa over a broad range of oxygen fugacities [log(fO2)=FMQ, FMQ+1.2, FMQ+3; FMQ = fayalite-magnetite-quartz solid buffer]. The data are used to test the hypothesis that S oxidation states other than S6+ may substitute into the apatite structure. Peak energies corresponding to sulfate S6+ (∼2482 eV), sulfite S4+ (∼2478 eV), and sulfide S2- (∼2470 eV) were observed in apatite, and the integrated areas of the different sulfur peaks correspond to changes in fO2 and bulk S content. Here, multiple tests confirmed that the S oxidation state in apatite remains constant when exposed to the synchrotron beam, at least for up to 1 h exposure (i.e., no irradiation damages). To our knowledge, this observation makes apatite the first mineral to incorporate reduced (S2-), intermediate (S4+), and oxidized (S6+) S in variable proportions as a function of the prevailing fO2 of the system. Apatites crystallized under oxidizing conditions (FMQ+1.2 and FMQ+3), where the S6+/STotal peak area ratio in the coexisting glass (i.e., quenched melt) is ∼1, are dominated by S6+ with a small contribution of S4+, whereas apatites crystallizing at reduced conditions (FMQ) contain predominantly S2-, lesser amounts of S6+, and possibly traces of S4+. A sulfur oxidation state vs. S concentration analytical line transect across hydrothermally altered apatite from the Mina Carmen iron oxide-apatite (IOA) deposit (Chile) demonstrates that apatite can become enriched in S4+ relative to S6+, indicating metasomatic overprinting via a SO2-bearing fluid or vapor phase. This XANES study demonstrates that as the fO2 increases from FQM to FMQ+1.2 to FMQ+3 the oxidation state of S in igneous apatite changes from S2- dominant to S6+ > S4+ to S6+ >> S4+ Furthermore, these results suggest that spectroscopic studies of igneous apatite have potential to trace the oxidation state of S in magmas. The presence of three S oxidations states in apatite may in part explain the non-Henrian partitioning of S between apatite and melt. Our study reveals the potential to use the S signature of apatite to elucidate both oxygen and sulfur fugacity in magmatic and hydrothermal systems.
  • Editor: Washington: Mineralogical Society of America
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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