
Sulfur isotope evolution in sulfide ores from Western Alps: Assessing the influence of subduction‐related metamorphism
Author(s) -
Giacometti Fabio,
Evans Katy A.,
Rebay Gisella,
Cliff John,
Tomkins Andrew G.,
Rossetti Piergiorgio,
Vaggelli Gloria,
Adams David T.
Publication year - 2014
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1002/2014gc005459
Subject(s) - geology , metamorphism , geochemistry , metamorphic rock , protolith , mantle wedge , pyrite , sulfide , mantle (geology) , δ34s , subduction , fluid inclusions , hydrothermal circulation , paleontology , chemistry , organic chemistry , tectonics
Sulfides entering subduction zones can play an important role in the release of sulfur and metals to the mantle wedge and contribute to the formation of volcanic arc‐associated ores. Fractionation of stable sulfur isotopes recorded by sulfides during metamorphism can provide evidence of fluid‐rock interactions during metamorphism and give insights on sulfur mobilization. A detailed microtextural and geochemical study was performed on mineralized samples from two ocean floor‐related sulfide deposits (Servette and Beth‐Ghinivert) in high‐pressure units of the Italian Western Alps, which underwent different metamorphic evolutions. The combination of microtextural investigations with δ 34 S values from in situ ion probe analyses within individual pyrite and chalcopyrite grains allowed evaluation of the effectiveness of metamorphism in modifying the isotopic record and mobilizing sulfur and metals and have insights on fluid circulation within the slab. Textures and isotopic compositions inherited from the protolith are recorded at Beth‐Ghinivert, where limited metamorphic recrystallization is attributed to limited interaction with metamorphic fluids. Isotopic modification by metamorphic processes occurred only at the submillimeter scale at Servette, where local interactions with infiltrating hydrothermal fluid are recorded by metamorphic grains. Notwithstanding the differences recorded by the two deposits, neither underwent intensive isotopic reequilibration or records evidence of intense fluid‐rock interaction and S mobilization during metamorphism. Therefore, subducted sulfide deposits dominated by pyrite and chalcopyrite are unlikely to release significant quantities of sulfur to the mantle wedge and to arc magmatism sources at metamorphic grades below the lower eclogite facies.