Sulphide-sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and time

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dc.contributor.authorCanil, Dante
dc.contributor.authorFellows, Steven A.
dc.date.accessioned2018-09-27T18:31:09Z
dc.date.copyright2017en_US
dc.date.issued2017
dc.description.abstractThe redox budget during subduction is tied to the evolution of oxygen and biogeochemical cycles on Earth's surface over time. The sulphide–sulphate couple in subducted crust has significant potential for redox and control on extraction of chalcophile metals from the arc mantle. We derive oxygen buffers for sulphide–sulphate stability (‘SSO buffers’) using mineral assemblages in subducted crust within the eclogite facies, and examine their disposition relative to the f02 in the arc mantle along various P–T trajectories for subduction. The f02 required for sulphide stability in subducted crust passing beneath an arc is shifted by variations in the bulk Ca/(Ca + Mg + Fe) of the subducting crust alone. Hotter slabs and more Fe-rich sediments stabilize sulphide and favour chalcophile sequestration deep into the mantle, whereas colder slabs and calcic sediment will stabilize anhydrite, in some cases at depths of melt generation in the arc mantle (<130 km). The released sulphate on melting potentially increases the f02 of the arc mantle. We performed melting experiments on three subducted sediment compositions varying in bulk Ca/(Ca + Mg + Fe) from 0.3 to 0.6 at 2.5 GPa and 900–1100 °C to confirm how anhydrite stability can change by orders of magnitude the S, Cu, As, Zn, Mo, Pb, and Sb contents of sediment melts, and their subsequent liberation to the arc mantle. Using Cu/Sc as a proxy for the behaviour of S, the effect of variable subducted sediment composition on sulphide–sulphate stability and release of chalcophiles to the arc mantle is recognizable in volcanic suites from several subduction zones in space and time. The f02 of the SSO buffers in subducted sediment relative to the arc mantle may have changed with time by shifts in the nature of pelagic sedimentation in the oceans over earth history. Oxidation of arc mantle and the proliferation of porphyry Cu deposits may be latter-day advents in earth history partly due to the rise of planktic calcifiers in the oceans in only the past 250 million years.en_US
dc.description.embargo2019-08-01
dc.description.reviewstatusRevieweden_US
dc.description.scholarlevelFacultyen_US
dc.description.sponsorshipThis research was supported by a NSERC of Canada Discovery Grant to DC.en_US
dc.identifier.citationCanil, D. & Fellows, S.A. (2017). Sulphide–sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and time. Earth and Planetary Science Letters, 470, 73-86. https://doi.org/10.1016/j.epsl.2017.04.028en_US
dc.identifier.urihttps://doi.org/10.1016/j.epsl.2017.04.028
dc.identifier.urihttp://hdl.handle.net/1828/10096
dc.language.isoenen_US
dc.publisherEarth and Planetary Science Lettersen_US
dc.subjectarc
dc.subjectredox
dc.subjectsulphur
dc.subjectsubduction
dc.subjectsediments
dc.subjectchalcophile
dc.subject.departmentSchool of Earth and Ocean Sciences
dc.titleSulphide-sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and timeen_US
dc.typePostprinten_US

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