TY - JOUR

T1 - Sulfur isotope signatures in the lower crust

T2 - A SIMS study on S-rich scapolite of granulites

AU - Hammerli, Johannes

AU - Kemp, Anthony I. S.

AU - Barrett, Natasha

AU - Wing, Boswell A.

AU - Roberts, Malcolm

AU - Arculus, Richard J.

AU - Boivin, Pierre

AU - Nude, Prosper M.

AU - Rankenburg, Kai

PY - 2017/4/5

Y1 - 2017/4/5

N2 - Scapolite is an important reservoir for volatiles in the deep crust and provides unique insights into the S isotope signatures at themantle/crust interface. Herewe document the first scapolite referencematerial (herein referred to as CB1) for in situ S isotope analysis. The chemical and isotopic composition of this euhedral, S-rich scapolite megacryst was characterized via LA-ICP-MS, EPMA, SIMS, and bulk fluorination gas source isotope ratio mass spectrometry. The CB1 scapolite is isotopically homogeneous and our results show that crystal orientation does not affect in situ S isotope SIMS analysis. This makes CB1 an ideal primary calibration standard for in situ analysis of S isotope ratios (S-36/S-32, S-34/S-32 and S-33/S-32) in scapolite. With this reference material in hand, we then applied in situ SIMS analysis of S isotopes for the first time on scapolite in granulite samples from the lower crust/upper mantle. The analysed sample suite comprises rocks from classic granulite xenolith locations in southeastern Australia, aswell as a sample fromthe high-grade suture zone of the Dahomeyides in south-eastern Ghana. The results show that scapolites in the lower crust have delta S-34 values between similar to-0.5 and + 4 (% VCDT). These values fallwithin the range of S isotope signatures present in mantle rocks and provide no evidence for the recycling of seawater-derived S into the lower crust. We propose that scapolite formed during granulite facies metamorphismof igneous cumulates, where Swas sourced fromprecursor igneous sulfides. Sulfur isotope heterogeneities between individual scapolite grains in some of the studied samples may reflect non-uniform Sisotope compositions of igneous S-phases, which precipitated from mantle-derived melt. (C) 2017 Elsevier B.V. All rights reserved.

AB - Scapolite is an important reservoir for volatiles in the deep crust and provides unique insights into the S isotope signatures at themantle/crust interface. Herewe document the first scapolite referencematerial (herein referred to as CB1) for in situ S isotope analysis. The chemical and isotopic composition of this euhedral, S-rich scapolite megacryst was characterized via LA-ICP-MS, EPMA, SIMS, and bulk fluorination gas source isotope ratio mass spectrometry. The CB1 scapolite is isotopically homogeneous and our results show that crystal orientation does not affect in situ S isotope SIMS analysis. This makes CB1 an ideal primary calibration standard for in situ analysis of S isotope ratios (S-36/S-32, S-34/S-32 and S-33/S-32) in scapolite. With this reference material in hand, we then applied in situ SIMS analysis of S isotopes for the first time on scapolite in granulite samples from the lower crust/upper mantle. The analysed sample suite comprises rocks from classic granulite xenolith locations in southeastern Australia, aswell as a sample fromthe high-grade suture zone of the Dahomeyides in south-eastern Ghana. The results show that scapolites in the lower crust have delta S-34 values between similar to-0.5 and + 4 (% VCDT). These values fallwithin the range of S isotope signatures present in mantle rocks and provide no evidence for the recycling of seawater-derived S into the lower crust. We propose that scapolite formed during granulite facies metamorphismof igneous cumulates, where Swas sourced fromprecursor igneous sulfides. Sulfur isotope heterogeneities between individual scapolite grains in some of the studied samples may reflect non-uniform Sisotope compositions of igneous S-phases, which precipitated from mantle-derived melt. (C) 2017 Elsevier B.V. All rights reserved.

KW - S-rich scapolite

KW - Lower crust

KW - Stable isotopes

KW - SIMS analyses

KW - Scapolite in granulites

KW - Sulfur cycle

KW - Sulfur flux

KW - ILMENITE-SERIES GRANITOIDS

KW - MASSIF-CENTRAL FRANCE

KW - NEW-SOUTH-WALES

KW - STABLE-ISOTOPE

KW - MANTLE XENOLITHS

KW - LITHOSPHERIC MANTLE

KW - SUBDUCTION ZONES

KW - MAGNETITE-SERIES

KW - PHOSPHORIC-ACID

KW - VOLCANIC-ROCKS

U2 - 10.1016/j.chemgeo.2017.02.016

DO - 10.1016/j.chemgeo.2017.02.016

M3 - Journal article

VL - 454

SP - 54

EP - 66

JO - Chemical Geology

JF - Chemical Geology

SN - 0009-2541

ER -