Abstract Transition metal isotopes are particularly useful for understanding the conditions under which magmatic processes occur. Moreover, those with more than one oxidation state (e.g. Cr2+, Cr3+ and Cr6+) may also provide powerful constraints on the evolution of the redox state of the mantle over time. By investigating the Cr isotopic compositions in both magnesiochromite and silicate melts during experiments performed at 1300 °C and under controlled redox conditions (−12 −6) are much lighter than those of melts equilibrated with magnesiochromite at lower oxygen fugacity. The observed variations can be explained by changes in bonding environment for Cr under oxidised conditions in the silicate melts and/or in the magnesiochromite grains. Similarly, the second set of experiments designed to study fractional crystallisation (series B) suggest that Cr isotope fractionation is larger under oxidising conditions.

中文翻译：

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氧化还原对与镁铬铁矿接触的硅酸盐熔体中铬同位素行为的控制

摘要 过渡金属同位素对于了解岩浆过程发生的条件特别有用。此外，那些具有不止一种氧化态的物质（例如 Cr2+、Cr3+ 和 Cr6+）也可能对地幔氧化还原态随时间的演变提供强有力的限制。通过研究在 1300 °C 和受控氧化还原条件 (-12 -6) 下进行的实验中镁铬铁矿和硅酸盐熔体中的 Cr 同位素组成，比在较低氧逸度下用镁铬铁矿平衡的熔体轻得多。观察到的变化可以通过在氧化条件下硅酸盐熔体和/或镁铬铁矿晶粒中 Cr 键合环境的变化来解释。相似地，