238U/235U systematics in terrestrial uranium-bearing minerals
Hiess, Joe; Condon, Daniel J.; McLean, Noah; Noble, Stephen R.. 2012 238U/235U systematics in terrestrial uranium-bearing minerals. Science, 335 (6076). 1610-1614. 10.1126/science.1215507Before downloading, please read NORA policies.
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.
|Programmes:||BGS Programmes 2010 > NERC Isotope Geoscience Laboratory|
|Additional Keywords:||geochronology; isotopes; zircon|
|NORA Subject Terms:||Earth Sciences
|Date made live:||02 Apr 2012 11:00|
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