Garnet crystallization does not drive oxidation at arcs

• 成果类型: Article
• 署名作者: Holycross, Megan; Cottrell, Elizabeth
• 署名单位: Cornell University; Smithsonian Institution; Smithsonian National Museum of Natural History
• 刊物名称: SCIENCE
• ISSN/ISSBN: 0036-11701
• DOI: 10.1126/science.ade3418
• 发表日期: 2023-05-05
• 页码: 506-509
• 关键词: oxygen fugacity; silicate melt; magmas; systematics; basalts; state; morb; clinopyroxene; gpa

摘要

Arc magmas, the building blocks of continental crust, are depleted in total iron (Fe), have higher ratios of oxidized Fe to total Fe (Fe3+/EFe), 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+/EFe 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.