| Summary: | <p>Measurements of isotopic ratios have been useful in understanding the formation and evolution
of planetary bodies in our Solar System. However, studies have typically been limited in
sample overlap, thereby limiting possible interpretation. This study presents the first highprecision
vanadium isotope data, zinc isotope data (via double-spiking), and trace-element data
for a suite of lunar basalts. Companion analyses of chlorine and sulphur isotope ratios were
obtained at University of New Mexico and University of Maryland.</p>
<p>Vanadium isotope ratios span a larger range (~2.5‰) within this suite of lunar basalts
than found in all igneous terrestrial rocks (~2.3‰). Lunar isotopic ratios are almost uniformly
lighter than those from the bulk silicate Earth (BSE). Unlike on Earth, variation in vanadium
isotope ratios is mainly due to cosmogenic effects, where bombardment of lunar samples by
energetic particles (from solar and galactic cosmic rays) alters primary isotopic compositions.
Modelling of cross-sections shows that iron is likely the most important target element in lunar
samples. Correcting for cosmogenic effects shows lunar basalts to have uniform vanadium
isotope ratios within error of recent estimates for the BSE. Where published meteorite data is
available, accounting for cosmogenic exposure shows no resolvable difference between the
BSE, Mars, Moon, and chondrites, in contrast to earlier studies.</p>
<p>Zinc displays a large isotopic range (~10‰) even amongst samples of the same
lithological subtype, likely reflecting the volatile behaviour of zinc. Chlorine isotope ratios for
the water-soluble fractions of the basalts in this suite (and for published data) correlate
negatively with zinc isotope ratios, indicating a mixing trend between a heavy-Zn, light-Cl
endmember, and a light-Zn, heavy-Cl endmember. Mobilisation of volatiles enriched in the
lunar crust during magmatic ascent or eruption is the most plausible explanation for this trend.</p>
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