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Separation of Uranium and Thorium for 230Th-U Dating of Submarine Hydrothermal Sulfides
Published on: May 20, 2019
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The terrestrial uranium isotope cycle
Morten B Andersen1, Tim Elliott2, Heye Freymuth2
11] Bristol Isotope Group, School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK [2] Institute of Geochemistry and Petrology, Department of Earth Sciences, ETH Zürich, 8092 Zürich, Switzerland.
Nature
|January 17, 2015
Summary
Recycled uranium from Earth's surface, altered by an oxygenated ocean, has distinct isotopic signatures. This uranium pollutes the upper mantle, influencing mid-ocean-ridge basalts but not ocean island basalts, indicating older mantle sources.
Area of Science:
- Geochemistry
- Isotope Geochemistry
- Earth Science
Background:
- Earth's surface conditions significantly impact its interior composition.
- Uranium distribution provides insight into early Earth history and mantle processes.
- The rise in atmospheric oxygen influenced uranium's mobility and transport.
Purpose of the Study:
- To investigate the isotopic characteristics of the global uranium cycle.
- To understand the impact of subducted uranium on mantle composition.
- To differentiate between mantle sources using uranium isotopes.
Main Methods:
- Analysis of uranium isotopic compositions ((238)U/(235)U ratios).
- Examination of mid-ocean-ridge basalts (MORBs) and ocean island basalts (OIBs).
- Comparison of isotopic data with existing lead model ages for OIBs.
Main Results:
- Subducted uranium exhibits high (238)U/(235)U ratios due to oxic ocean alteration.
- MORBs show elevated (238)U/(235)U ratios, indicating upper mantle contamination by recycled uranium.
- OIBs do not show distinct uranium isotopic compositions compared to the bulk Earth, suggesting older mantle sources.
Conclusions:
- Recycled uranium has measurably altered the upper mantle within the last 600 million years.
- Uranium isotope systematics in OIBs support mantle reservoir formation between 2.4 and 1.8 billion years ago.
- The distinct isotopic signature of recycled uranium highlights its significant role in global geochemical cycles.
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