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A New Appraisal of Sri Lankan BB Zircon as a Reference Material for LA‐ICP‐MS U‐Pb Geochronology and Lu‐Hf Isotope Tracing |
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| Authors: | Maristella M. Santos Cristiano Lana Ricardo Scholz Ian Buick Mark D. Schmitz Sandra L. Kamo Axel Gerdes Fernando Corfu Simon Tapster Penelope Lancaster Craig D. Storey Miguel A.S. Basei Eric Tohver Ana Alkmim Herminio Nalini Klaus Krambrock Cristiano Fantini Michael Wiedenbeck |
| Affiliation: | 1. Applied Isotope Research Group, Departamento de Geologia, Escola de Minas, Universidade Federal de Ouro Preto, Ouro Preto, MG, Brazil;2. Instituto Federal de Minas Gerais (IFMG), Campus Congonhas, Minas Gerais, Brazil;3. Department of Earth Sciences, Centre for Crustal Petrology, Stellenbosch University, Matieland, Stellenbosch, South Africa;4. Department of Geosciences, Boise State University, Boise, ID, USA;5. Jack Satterly Geochronology Laboratory, Department of Earth Sciences, University of Toronto, Toronto, ON, Canada;6. Institute of Geosciences, Johann Wolfgang Goethe University, Frankfurt am Main, Germany;7. Department of Geosciences, University of Oslo, Oslo, Norway;8. NERC Isotope Geosciences Laboratory, British Geological Survey, Kingsley Dunham Centre, Keyworth, Nottingham, UK;9. School of Earth and Environmental Sciences, Burnaby Building, University of Portsmouth, Portsmouth, UK;10. Centro de Pesquisas Geocronológicas – CPGeo/IGc – USP, S?o Paulo, SP, Brazil;11. Tectonics Special Research Centre, University of Western Australia, Perth, WA, Australia;12. Departamento de Física, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil;13. Deutsches GeoForschungsZentrum, Potsdam, Germany |
| Abstract: | A potential zircon reference material (BB zircon) for laser ablation‐inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) U‐Pb geochronology and Hf isotope geochemistry is described. A batch of twenty zircon megacrysts (0.5–1.5 cm3) from Sri Lanka was studied. Within‐grain rare earth element (REE) compositions are largely homogeneous, albeit with some variation seen between fractured and homogeneous domains. Excluding fractured cathodoluminescence bright domains, the variation in U content for all analysed crystals ranged from 227 to 368 μg g?1 and the average Th/U ratios were between 0.20 and 0.47. The Hf isotope composition (0.56–0.84 g/100 g Hf) is homogeneous within and between the grains – mean 176Hf/177Hf of 0.281674 ± 0.000018 (2s). The calculated alpha dose of 0.59 × 1018 g?1 for a number of BB grains falls within the trend of previously studied, untreated zircon samples from Sri Lanka. Aliquots of the same crystal (analysed by ID‐TIMS in four different laboratories) gave consistent U‐Pb ages with excellent measurement reproducibility (0.1–0.4% RSD). Interlaboratory assessment (by LA‐ICP‐MS) from individual crystals returned results that are within uncertainty equivalent to the TIMS ages. Finally, we report on within‐ and between‐grain homogeneity of the oxygen isotope systematic of four BB crystals (13.16‰ VSMOW). |
| Keywords: | BB zircon Sri Lankan reference material U‐Pb geochronology Hf isotope system rare earth elements LA‐ICP‐MS |