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In situ Oxygen Isotope Determination in Serpentine Minerals by Ion Microprobe: Reference Materials and Applications to Ultrahigh-Pressure Serpentinites

Type of publication Peer-reviewed
Publikationsform Original article (peer-reviewed)
Author Scicchitano Maria Rosa, Rubatto Daniela, Hermann Jörg, Shen Tingting, Padrón-Navarta J.A., Williams I S, Zheng Y. F.,
Project Tracing the invisible path of fluids in the crust with microscale oxygen isotope measurements in key metamorphic minerals
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Original article (peer-reviewed)

Journal Geostandards and geoanalytical research
Page(s) 1
Title of proceedings Geostandards and geoanalytical research
DOI 10.1111/ggr.12232

Open Access

URL https://boris.unibe.ch/id/eprint/121891
Type of Open Access Green OA Embargo (Freely available via Repository after an embargo)

Abstract

We present the first investigation of in situ oxygen isotopes in serpentine minerals by sensitive high-resolution ion microprobe (SHRIMP). Chemically homogeneous samples of antigorite (d18O = 8.30 ± 0.12‰), chrysotile (d18O = 4.37 ± 0.02‰) and lizardite (d18O = 5.26 ± 0.20‰) analysed by laser fluorination are identified as potential reference materials. They were analysed by SHRIMP to assess their homogeneity compared with the San Carlos olivine, as well as for potential matrix bias and crystal orientation effects. The reproducibility achieved for all samples was ± 0.30–0.55‰ (95% confidence level). Matrix bias between antigorite/olivine and antigorite/lizardite was up to ~ +3‰ and - 1‰, respectively. Crystal orientation effects were identified only in chrysotile, and no matrix bias was observed over the investigated compositional range within each serpentine mineral. The new reference materials were used to measure the oxygen isotope composition of serpentines in an ultrahigh-pressure metamorphic belt from Tianshan (China). By combining oxygen isotopes and trace element microanalyses, several stages of serpentinisation were recognised: (a) seafloor alteration, (b) recycling of internal metamorphic fluids during isothermal decompression and (c) shallow interaction with meteoric water during exhumation. No interaction with fluids derived from the surrounding metapelites during subduction was identified.
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