This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.1126/science.1215507. This is version 1 of this Preprint.
238U/235U Systematics in Terrestrial Uranium-Bearing Minerals
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Abstract
The present-day 238U/235U ratio has fundamental implications for uranium-lead geochronology and cosmochronology. A value of 137.88 has previously been considered invariant and has been used without uncertainty to calculate terrestrial mineral ages. We report high-precision 238U/235U measurements for a suite of uranium-bearing minerals from 58 samples representing a diverse range of lithologies. This data set exhibits a range in 238U/235U values of >5 per mil, with no clear relation to any petrogenetic, secular, or regional trends. Variation between comagmatic minerals suggests that 238U/235U fractionation processes operate at magmatic temperatures. A mean 238U/235U value of 137.818 ± 0.045 (2σ) in zircon samples reflects the average uranium isotopic composition and variability of terrestrial zircon. This distribution is broadly representative of the average crustal and “bulk Earth” 238U/235U composition.
DOI
https://doi.org/10.31223/osf.io/e2qxt
Subjects
Chemistry, Cosmochemistry, Earth Sciences, Geochemistry, Inorganic Chemistry, Physical Sciences and Mathematics
Keywords
Geochronology, Zircon, EARTHTIME
Dates
Published: 2017-11-05 12:24
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