High precision iron isotope measurements of terrestrial and lunar materials |
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| Institution: | 1. State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;2. Geology and Geophysics, University of Utah, Salt Lake City, UT, United States;3. School of Earth, Atmosphere and Environment, Monash University, 3800 Clayton, VIC, Australia;4. State Key Laboratory of Geological Processes and Mineral Resources, School of Earth Sciences, China University of Geosciences, Wuhan 430074, China;5. Key Laboratory of Marine Mineral Resources of Ministry of Natural Resources, Guangzhou Marine Geological Survey, Guangzhou 511458, China;1. School of the Environment, Trent University, Peterborough, Canada;2. Department of Chemistry, Trent University, Peterborough, Canada;3. Water Quality Center, Trent University, Peterborough, Canada;4. Department of Earth & Planetary Sciences, Yale University, New Haven, USA;5. CSIRO Mineral Resources, Australian Resources Research Centre, Kensington, Australia;6. School of Earth and Environmental Sciences, Cardiff University, Cardiff, UK;7. Department of Earth & Planetary Sciences and Geotop, McGill University, Montreal, Canada |
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| Abstract: | We present the analytical methods that have been developed for the first high-precision Fe isotope analyses that clearly identify naturally-occurring, mass-dependent isotope fractionation. A double-spike approach is used, which allows rigorous correction of instrumental mass fractionation. Based on 21 analyses of an ultra pure Fe standard, the external precision (1-SD) for measuring the isotopic composition of Fe is ±0.14 ‰/mass; for demonstrated reproducibility on samples, this precision exceeds by at least an order of magnitude that of previous attempts to empirically control instrumentally-produced mass fractionation (Dixon et al., 1993). Using the double-spike method, 15 terrestrial igneous rocks that range in composition from peridotite to rhyolite, 5 high-Ti lunar basalts, 5 Fe-Mn nodules, and a banded iron formation have been analyzed for their iron isotopic composition. The terrestrial and lunar igneous rocks have the same isotopic compositions as the ultra pure Fe standard, providing a reference Fe isotope composition for the Earth and Moon. In contrast, Fe-Mn nodules and a sample of a banded iron formation have iron isotope compositions that vary over a relatively wide range, from δ56Fe = +0.9 to ?1.2 ‰; this range is 15 times the analytical errors of our technique. These natural isotopic fractionations are interpreted to reflect biological (“vital”) effects, and illustrate the great potential Fe isotope studies have for studying modern and ancient biological processes. |
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