The vanadium isotopic composition of lunar basalts
The vanadium isotopic composition of lunar basalts
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DOI：
10.1016/j.epsl.2019.01.008
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发表时间：
2019-04
影响因子：
5.3
通讯作者：
S. Hopkins;J. Prytulak;J. Barling;S. Russell;B. Coles;A. Halliday
中科院分区：
文献类型：
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作者：
S. Hopkins;J. Prytulak;J. Barling;S. Russell;B. Coles;A. Halliday
我们首次获得了月球玄武岩的高精度钒（V）同位素数据。陆地岩浆岩测量可以显示显着的V同位素分馏（特别是在（Fe，Ti）氧化物结晶），但地球显示重V（即较高的51 V/50 V）同位素组成相比，陨石。这被归因于陨石成分的早期辐照或核合成的异质性。月球的许多难熔元素与硅酸盐地球的同位素无法区分，预计其V同位素组成相似。对19个月面玄武岩样品进行了钒同位素比值和微量元素含量测定。同位素组成比迄今为止在陆地火成岩中发现的变化更大（102.5 ‰），并延伸到更轻的值。岩浆过程似乎不控制的V同位素组成，尽管在套房的氧化物比例的大范围。相反，V同位素组成的月球样品是轻的暴露年龄（吨）的增加。模拟核截面的V生产和燃尽表明，宇宙成因的生产可能会影响V同位素比，通过一些渠道，但V同位素比之间的强相关性和铁[Fe]/[V]暗示Fe作为主要目标元素的重要性。相似的相关性被发现在最新的数据，提供的证据表明，大多数V同位素的变化，在辉长岩是由于最近的宇宙成因生产通过Fe sparterium。与之前的建议相反，没有证据表明地球、月球、球粒陨石和火星的主要V同位素组成之间存在可解决的差异。
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 (ie 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.