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Vanadium isotope fractionation of alkali basalts during mantle melting
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Date
2023-02-22
Authors
Chen, Zhenwu
Ding, Xin
Kiseeva, Ekaterina S.
Lin, Xiaobao
Huang, Jian
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier B.V.
Published Version
Abstract
It is well known that vanadium (V) is redox-sensitive during magmatism, but whether V isotopes can be used as a mantle oxygen fugacity (fO2) sensor remains controversial. Before using V isotopes as a redox proxy, it is crucial to understand the fractionation behavior and controlling factors of V isotopes during mantle melting. This study reports high-precision V isotopic data for alkali basalts with high fO2 in eastern China, which were derived from carbonated mantle by a low degree of partial melting. Our results show that their δ51V values (−0.85‰ to −0.61‰) are higher than those of bulk silicate Earth (BSE) and mid-ocean ridge basalts (MORBs). Chemical alteration, crustal contamination or fractional crystallization negligibly affect the δ51V values of alkali basalts. Although subducted carbonates are involved in the mantle source region under eastern China, mass balance calculations show that the incorporation of carbonates did not significantly increase the δ51V values of alkali basalts. In contrast, the observed high δ51V values probably reflect that mantle melting controls the V isotopic compositions of mantle-derived melts. The relative abundances of V5+, V4+ and V3+ in silicate melt are influenced by the variation of fO2 and/or the degree of partial melting. Basaltic melts tend to be enriched in V with high valence at the condition of high fO2 during mantle melting, which contributes to the enrichment of 51V in alkali basalts because of the affinity of high valence V and 51V. Because mantle minerals are overall more compatible of V with low valence, the valence states of V in silicate melt tend to be higher at low degree of partial melting, resulting in more significant fractionation of V isotopes. Therefore, this study validates discernable V isotope fractionation during partial melting of the mantle and examines the potential of using V isotopes to trace the redox state of magmatic systems.
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Keywords
Alkali basalt , Vanadium isotopes , Partial melting , Oxygen fugacity , Carbonate cycling
Citation
Chen, Z., Ding, X., Kiseeva, E. S., Lin, X., Huang, J. and Huang, F. (2023) 'Vanadium isotope fractionation of alkali basalts during mantle melting', Lithos, 442-443, 107082 (10pp). doi: 10.1016/j.lithos.2023.107082