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The vanadium isotopic composition of lunar basalts

Abstract:
We present the first high-precision vanadium (V) isotope data for lunar basalts. Terrestrial magmatic rock measurements can display significant V isotopic fractionation (particularly during (Fe, Ti)oxide crystallisation), but the Earth displays heavy V (i.e. higher 51 V/ 50 V) isotopic compositions compared to meteorites. This has been attributed to early irradiation of meteorite components or nucleosynthetic heterogeneity. The Moon is isotopically-indistinguishable from the silicate Earth for many refractory elements and is expected to be similar in its V isotopic composition. Vanadium isotope ratios and trace element concentrations were measured for 19 lunar basalt samples. Isotopic compositions are more variable (∼2.5‰) than has been found thus far for terrestrial igneous rocks and extend to lighter values. Magmatic processes do not appear to control the V isotopic composition, despite the large range in oxide proportions in the suite. Instead, the V isotopic compositions of the lunar samples are lighter with increasing exposure age (t e ). Modelling nuclear cross-sections for V production and burnout demonstrates that cosmogenic production may affect V isotope ratios via a number of channels but strong correlations between V isotope ratios and t e⁎ [Fe]/[V] implicate Fe as the primary target element of importance. Similar correlations are found in the latest data for chondrites, providing evidence that most V isotope variation in chondrites is due to recent cosmogenic production via Fe spallation. Contrary to previous suggestions, there is no evidence for resolvable differences between the primary V isotopic compositions of the Earth, Moon, chondrites and Mars.
Publication status:
Published
Peer review status:
Peer reviewed

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Publisher copy:
10.1016/j.epsl.2019.01.008

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Institution:
University of Oxford
Division:
MPLS
Department:
Earth Sciences
Role:
Author
ORCID:
0000-0001-8535-5262


Publisher:
Elsevier
Journal:
Earth and Planetary Science Letters More from this journal
Volume:
511
Pages:
12-24
Publication date:
2019-02-01
Acceptance date:
2019-01-03
DOI:
ISSN:
1385-013X and 0012-821X


Keywords:
Pubs id:
pubs:971646
UUID:
uuid:bfab5ab7-b1d5-4754-8ec8-3c250d936b42
Local pid:
pubs:971646
Source identifiers:
971646
Deposit date:
2019-05-07

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