石榴石结晶实际不会导致弧氧化，这一结论由美国康奈尔大学Megan Holycross的课题组提出。该研究于2023年5月5日发表于国际一流学术期刊《科学》杂志上。

研究人员在实验室中对石榴石和熔体进行分析，表明石榴石中的Fe²⁺和Fe³⁺的相容性具有相似的数量级。研究结果表明，含石榴石堆积体的分离结晶将从原生岛弧玄武岩中祛除20%的总铁，但对熔体的Fe³⁺ /∑Fe的改变可忽略不计。石榴石结晶不可能是玄武岩弧岩浆相对氧化性质或在大陆地壳中观察到的，铁贫化趋势的原因。

据悉，与在大洋中脊喷发的岩浆相比，构成大陆地壳的弧岩浆贫乏总铁(Fe)，氧化铁与总铁的比率(Fe³⁺ /∑Fe)更高，氧逸度(fO^,s)也更高。如果石榴石从岩浆中祛除了大量的Fe²⁺，而不是Fe³⁺，石榴石结晶可以解释这些观察结果，然而这种大陆地壳的生成模型从未经过测试。

附：英文原文

Title: Garnet crystallization does not drive oxidation at arcs

Author: Megan Holycross, Elizabeth Cottrell

Issue&Volume: 2023-05-05

Abstract: Arc magmas, the building blocks of continental crust, are depleted in total iron (Fe), have higher ratios of oxidized Fe to total Fe (Fe³⁺ /∑Fe), and record higher oxygen fugacities (fO₂^’s) compared with magmas erupted at mid-ocean ridges. Garnet crystallization could explain these observations if garnet removes substantial amounts of Fe²⁺, but not Fe³⁺, from magma, yet this model for continental crust generation has never been tested experimentally. Analysis of garnets and melts in laboratory experiments show that the compatibilities of Fe²⁺ and Fe³⁺ in garnet are of similar magnitudes. Our results indicate that fractional crystallization of garnet-bearing cumulates will remove 20% of total Fe from primary arc basalts but negligibly alter the Fe³⁺ /∑Fe ratio and fO2 of the melt. Garnet crystallization is unlikely to be responsible for the relatively oxidized nature of basaltic arc magmas or the Fe-depletion trend observed in continental crust.

DOI: ade3418

Source: https://www.science.org/doi/10.1126/science.ade3418