GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 258-10
Presentation Time: 9:00 AM-6:30 PM


HAMMERLI, Johannes1, KEMP, Tony I.S.1, CRAVEN, John2, BARRETT, Natasha1, WING, Boswell3, ARCULUS, Richard J.4, ROBERTS, Malcolm5, BOIVIN, Pierre6 and NUDE, Prosper M.7, (1)The University of Western Australia, Centre for Exploration Targeting, Perth, 6009, Australia, (2)University of Edinburgh, Edinburgh Ion Microprobe Facility, School of Geosciences, Edinburgh, EH9 3FE, (3)Department of Earth and Planetary Sciences, McGill University, 3450 University Street, Montreal, QC H3A 2A7, Canada, (4)Research School of Earth Sciences, The Australian National Univ, ACT, Canberra, 0200, Australia, (5)The University of Western Australia, Centre for Microscopy Characterisation and Analysis, Perth, 6009, Australia, (6)Université Blaise Pascal Clermont-Ferrand, Laboratoire Magmas et Volcans (LMV), Clermont-Ferrand, 63178, France, (7)University of Ghana, Department of Earth Sciences, Accra, P. O. Box LG 25, Ghana,

The global sulfur (S) cycle has attracted vast interest across various disciplines, as S is a crucial element for a wide range of processes including the evolution of the atmosphere and potentially also the oxidation of the sub-arc mantle. One key process in global S (re-) cycling is the subduction of oceanic crust together with sediments and seawater and the subsequent release of S-bearing fluids from the subducted slab. It has been hypothesized that S derived from subducted slab material is recycled via the mantle into the overlying arc. However, it is not well understood how this subduction-derived S interacts with the mantle S reservoir, nor how S is transported via fluids through the sub-arc mantle and crust. The interface between the mantle and the crust has been poorly studied in terms of S isotope systematics. Here, we explore S isotope signatures in the lower crust via in situ (SIMS) S isotope analysis of S-rich scapolite hosted in granulites. S-rich scapolite has a restricted stability at conditions found in the lower crust, and is typically formed during granulite-facies metamorphism under oxidized conditions, where scapolite often occurs as the only S-bearing mineral. Therefore, scapolite is a suitable mineral to trace fluid fluxes from the subducting slab and mantle through to the overlying crust. In this study we present a large scapolite crystal (CB1) as a suitable standard for in situ S isotope analysis in scapolite due to its homogeneity and lack of inclusions. We applied SIMS analysis to several scapolite-bearing granulite xenoliths from the Delegate Breccia Pipes locality in New South Wales, Australia, and a scapolite-bearing granulite from Shai Hills, southeastern Ghana. Our results show that the S isotope signatures fall within the same range as typically found in the upper mantle (d34S ~­­–0.3 to ~4.2 ‰). Given the mantle-like d34S signature, a major seawater component (d34S >>5) was not likely to be present at the time of scapolite formation. Our results, together with previous studies, challenge the concept that slab-derived fluids play a key role in enriching arc magmas in 34S.