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Updated: May 23, 2026
08:43
Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides
Published on: May 20, 2019
238U/235U Systematics in terrestrial uranium-bearing minerals.
Joe Hiess1, Daniel J Condon, Noah McLean
1NERC Isotope Geoscience Laboratory, British Geological Survey, Keyworth, Nottinghamshire, UK. jies@bgs.ac.uk
Science (New York, N.Y.)
|March 31, 2012
Summary
The uranium-238/uranium-235 ratio is not constant, challenging its use in dating minerals. New measurements reveal variations, impacting uranium-lead geochronology and our understanding of Earth's composition.
Area of Science:
- Geochemistry
- Isotope Geology
- Radiometric Dating
Background:
- The present-day Uranium-238/Uranium-235 ratio is crucial for uranium-lead geochronology and cosmochronology.
- A previously assumed invariant ratio of 137.88 has been used without uncertainty for calculating terrestrial mineral ages.
Purpose of the Study:
- To investigate the variability of the present-day Uranium-238/Uranium-235 ratio in terrestrial minerals.
- To assess the implications of this variability for uranium-lead geochronology and cosmochronology.
Main Methods:
- High-precision Uranium-238/Uranium-235 ratio measurements were performed on uranium-bearing minerals from 58 diverse lithological samples.
- Analysis included a range of mineral types to capture isotopic variations.
Main Results:
- A significant range of over 5 per mil in Uranium-238/Uranium-235 values was observed across the samples.
- No clear correlation was found with petrogenetic, secular, or regional trends, suggesting localized fractionation.
- Variations between comagmatic minerals indicate Uranium-238/Uranium-235 fractionation occurs at magmatic temperatures.
Conclusions:
- The Uranium-238/Uranium-235 ratio is demonstrably variable, necessitating adjustments in geochronological calculations.
- A mean Uranium-238/Uranium-235 value of 137.818 ± 0.045 (2σ) in zircons represents terrestrial zircon isotopic composition and variability.
- This observed distribution is broadly representative of average crustal and bulk Earth Uranium-238/Uranium-235 compositions.
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