Deep crustal assimilation during the 2021 Fagradalsfjall Fires, Iceland

• 成果类型: Article
• 署名作者: Day, James M. D.; Kelly, Savannah; Troll, Valentin R.; Moreland, William M.; Cook, Geoffrey W.; Thordarson, Thor
• 署名单位: University of California System; University of California San Diego; Scripps Institution of Oceanography; Uppsala University; Uppsala University; Centre of Natural Hazards & Disaster Science (CNDS); University of Iceland
• 刊物名称: Nature
• ISSN/ISSBN: 0028-6933
• DOI: 10.1038/s41586-024-07750-0
• 发表日期: 2024-08-15
• 页码: 564-+
• 关键词: platinum-group elements; mantle; ridge; contamination; deformation; component; eruption; volcano; magmas; oxygen

摘要

Active basaltic eruptions enable time-series analysis of geochemical and geophysical properties, providing constraints on mantle composition and eruption processes(1-4). The continuing Fagradalsfjall and Sundhnukur fires on Iceland's Reykjanes Peninsula, beginning in 2021, enable such an approach(5,6). Earliest lavas of this volcanic episode have been interpreted to exclusively reflect a change from shallow to deeper mantle source processes(7). Here we show using osmium (Os) isotopes that the 2021 Fagradalsfjall lavas are both fractionally crystallized and strongly crustally contaminated, probably by mid-ocean-ridge gabbros and older basalts underlying the Reykjanes Peninsula. Earliest eruptive products (Os-187/Os-188 <= 0.188, platinum (Pt)/iridium (Ir)<= 76) are highly anomalous for Icelandic lavas or global oceanic basalts and Os isotope ratios remain elevated throughout the 2021 eruption, indicating a continued but diluted presence of contaminants. The 2022 lavas show no evidence for contamination (Os-187/Os-188=0.131, Pt/Ir=30), being typical of Icelandic basalts (0.1320.007). Initiation of the Fagradalsfjall Fires in 2021 involved pre-eruptive stalling, fractional crystallization and crustal assimilation of earliest lavas. An established magmatic conduit system in 2022 enabled efficient magma transit to the surface without crustal assimilation.