238U/235U Systematics in Terrestrial Uranium-Bearing Minerals

This is a Preprint and has not been peer reviewed.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.

Downloads

Download Preprint

Supplementary Files
Authors

Joe Hiess, Daniel Condon , Noah McLean , Stephen R Noble

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 14:24

Older Versions
License

Academic Free License (AFL) 3.0

Add a Comment

You must log in to post a comment.


Comments

There are no comments or no comments have been made public for this article.