The stable vanadium isotope composition of the mantle and mafic lavas
The stable vanadium isotope composition of the mantle and mafic lavas
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地幔和镁铁质熔岩的稳定钒同位素组成
DOI：
10.1016/j.epsl.2013.01.010
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发表时间：
2013
影响因子：
5.3
通讯作者：
Prytulak J
中科院分区：
文献类型：
--
作者：
Prytulak J
钒在陆地条件下以多种价态存在（2+、3+、4+、5+），其同位素组成可能反映了地幔源区的氧化状态。我们提出了第一个稳定的钒同位素测量的64个样品的特点，幔源镁铁质和超镁铁质岩石从不同的地方。δ 51 V的范围为−0.27‰至−1.29‰，相对于Alfa Aesar（AA）钒溶液标准定义为0‰。该数据集用于评估蚀变的影响，检查与其他地球化学特征的共变，并定义散装硅酸盐地球（BSE）的值。可变蛇纹橄榄岩没有可分辨的蚀变诱导δ 51 V分馏。同样，蚀变镁铁质洋壳岩石的δ 51 V与新鲜手工挑选的MORB玻璃相同。强烈的海底风化作用可导致同位素组成稍重（约0.2-0.3‰），可能与后期钒的加入有关。δ 51 V对常见蚀变过程的稳健性预示着其在古镁铁质物质中的潜在应用。基性熔岩（包括MORB、冰岛拉斑玄武岩和来自沙茨基海隆大火成岩省的熔岩）的平均δ 51 V为−0.88±0.27‰ 2sd。橄榄岩的原生δ 51 V变化范围很大（−0.62‰至−1.17‰），与钒浓度和Al 2 O3等肥力指标呈正相关。虽然这些数据表明在部分熔融过程中较重的同位素优先被提取，但玄武岩的同位素组成（δ 51 V =−0.88±0.27‰ 2sd），特别是MORB玻璃（δ 51 V =−0.95±0.13‰ 2sd）比肥沃的橄榄岩轻，因此很难与熔融提取情景相一致。熔体和矿物相，如辉石和石榴石之间的分馏系数的测定是必要的，以充分了解的相关性。通过对肥沃的、未交代的橄榄岩进行平均，我们得到块状硅酸盐地球的δ 51 VBSE =−0.7±0.2‰（2sd）。这为解决行星形成、地球和地外物质的宇宙化学比较以及未来地球化学调查的无机基线的高温和低温应用提供了基准。虽然δ 51 V可能与氧化态有关，因此与氧逸度有关，但需要进一步的工作来解决氧化态、部分熔融和矿物分馏因素的同位素效应。
Vanadium exists in multiple valence states under terrestrial conditions (2+, 3+, 4+, 5+) and its isotopic composition in magmas potentially reflects the oxidation state of their mantle source. We present the first stable vanadium isotope measurements of 64 samples of well-characterized mantle-derived mafic and ultramafic rocks from diverse localities. The δ51V ranges from −0.27‰ to −1.29‰, reported relative to an Alfa Aesar (AA) vanadium solution standard defined as 0‰. This dataset is used to assess the effects of alteration, examine co-variation with other geochemical characteristics and define a value for the bulk silicate Earth (BSE). Variably serpentinised peridotites show no resolvable alteration-induced δ51V fractionation. Likewise, altered mafic oceanic crustal rocks have identical δ51V to fresh hand-picked MORB glass. Intense seafloor weathering can result in slightly (∼0.2–0.3‰) heavier isotope compositions, possibly related to late-stage addition of vanadium. The robustness of δ51V to common alteration processes bodes well for its potential application to ancient mafic material. The average δ51V of mafic lavas, including MORB, Icelandic tholeiites and lavas from the Shatsky Rise large igneous province is −0.88±0.27‰ 2sd. Peridotites show a large range in primary δ51V (−0.62‰ to −1.17‰), which co-varies positively with vanadium concentrations and indices of fertility such as Al2O3. Although these data suggest preferential extraction of heavier isotopes during partial melting, the isotope composition of basalts (δ51V=−0.88±0.27‰ 2sd) and MORB glass in particular (δ51V=−0.95±0.13‰ 2sd) is lighter than fertile peridotites and thus difficult to reconcile with a melt extraction scenario. Determination of fractionation factors between melt and mineral phases such as pyroxenes and garnet are necessary to fully understand the correlation. We arrive at an estimate of δ51VBSE=−0.7±0.2‰ (2sd) for the bulk silicate Earth by averaging fertile, unmetasomatised peridotites. This provides a benchmark for both high and low temperature applications addressing planet formation, cosmochemical comparisons of the Earth and extraterrestrial material, and an inorganic baseline for future biogeochemical investigations. Whilst δ51V could relate to oxidation state and thus oxygen fugacity, further work is required to resolve the isotopic effects of oxidation state, partial melting, and mineral fractionation factors.
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DOI：
--
发表时间：
1985
期刊：
影响因子：
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