The vanadium isotopic composition of lunar basalts

Hopkins, S.S.; Prytulak, J.; Barling, J.; Russell, S.S.; Coles, B.J.; Halliday, A.N.

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 51V/50V) 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 (). 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 ⁎ [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.

Citation

Hopkins, S., Prytulak, J., Barling, J., Russell, S., Coles, B., & Halliday, A. (2019). The vanadium isotopic composition of lunar basalts. Earth and Planetary Science Letters, 511, 12-24. https://doi.org/10.1016/j.epsl.2019.01.008

• Journal Article Type: Article
• Acceptance Date: Jan 3, 2019
• Online Publication Date: Feb 1, 2019
• Publication Date: Feb 1, 2019
• Deposit Date: Feb 1, 2019
• Publicly Available Date: Feb 5, 2019
• Journal: Earth and Planetary Science Letters
• Print ISSN: 0012-821X
• Electronic ISSN: 1385-013X
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 511
• Pages: 12-24
• DOI: https://doi.org/10.1016/j.epsl.2019.01.008
• Public URL: https://durham-repository.worktribe.com/output/1308726