Osmium Isotopes Reveal Crustal Assimilation in 2021 Fagradalsfjall Eruptions, Iceland

핵심 개념

The 2021 Fagradalsfjall eruptions in Iceland involved fractional crystallization and significant crustal contamination, while the 2022 eruptions showed no evidence of crustal assimilation.

초록

The content discusses the geochemical analysis of the 2021 and 2022 Fagradalsfjall eruptions in Iceland. The key insights are:

1. The earliest 2021 Fagradalsfjall lavas show highly anomalous osmium (Os) isotope ratios (187Os/188Os ≤ 0.188) and platinum (Pt)/iridium (Ir) ratios (≤ 76), indicating significant crustal contamination, likely from mid-ocean-ridge gabbros and older basalts underlying the Reykjanes Peninsula.

2. The elevated Os isotope ratios persisted throughout the 2021 eruption, suggesting a continued but diluted presence of crustal contaminants.

3. In contrast, the 2022 Fagradalsfjall lavas showed no evidence of crustal assimilation, with Os isotope ratios (187Os/188Os = 0.131) and Pt/Ir ratios (30) typical of Icelandic basalts.

4. The authors propose that the initiation of the 2021 Fagradalsfjall eruptions involved pre-eruptive stalling, fractional crystallization, and crustal assimilation of the earliest lavas. However, an established magmatic conduit system in 2022 enabled efficient magma transit to the surface without significant crustal contamination.

5. The study demonstrates the value of time-series geochemical analysis of active basaltic eruptions, which can provide insights into mantle composition and eruption processes.

통계

The earliest 2021 Fagradalsfjall lavas have 187Os/188Os ≤ 0.188 and Pt/Ir ≤ 76.
The 2022 Fagradalsfjall lavas have 187Os/188Os = 0.131 and Pt/Ir = 30.

인용구

"Earliest eruptive products (187Os/188Os ≤ 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 (187Os/188Os = 0.131, Pt/Ir = 30), being typical of Icelandic basalts (0.132 ± 0.007)."

핵심 통찰 요약

Deep crustal assimilation during the 2021 Fagradalsfjall Fires, Iceland - Nature

by James M. D. ... 게시일 www.nature.com 07-31-2024

https://www.nature.com/articles/s41586-024-07750-0

더 깊은 질문

What other geochemical or geophysical signatures could be used to further investigate the crustal assimilation processes in the Fagradalsfjall eruptions?

To further investigate the crustal assimilation processes in the Fagradalsfjall eruptions, additional geochemical and geophysical signatures could be utilized. One approach could involve the analysis of other trace elements such as strontium (Sr), neodymium (Nd), and lead (Pb) isotopes. These elements can provide insights into the source of the contaminants and the extent of crustal assimilation. Additionally, studying the volatile elements like water (H2O), carbon dioxide (CO2), and sulfur (S) can help in understanding the degassing processes and the role of volatiles in magma contamination. Geophysical methods such as seismic imaging and gravity surveys can also be employed to map the subsurface structures and identify potential pathways for magma ascent, which can aid in tracing the interactions between the magma and crustal materials.

How might the observed crustal contamination affect the interpretation of the mantle source composition and melting processes beneath the Reykjanes Peninsula?

The observed crustal contamination in the Fagradalsfjall eruptions can significantly impact the interpretation of the mantle source composition and melting processes beneath the Reykjanes Peninsula. The presence of contaminants from mid-ocean-ridge gabbros and older basalts suggests that the mantle-derived magmas have interacted with the crustal materials during their ascent. This contamination can alter the geochemical signature of the erupted lavas, making it challenging to distinguish between the contributions from the mantle source and the crustal assimilants. As a result, the traditional geochemical tracers used to infer mantle compositions may be biased by the crustal components, leading to erroneous interpretations of the mantle source characteristics and melting processes. It is crucial to account for the crustal contamination effects to accurately constrain the mantle source compositions and understand the magmatic processes beneath the Reykjanes Peninsula.

What implications do the differences in crustal assimilation between the 2021 and 2022 eruptions have for the long-term evolution and behavior of the Fagradalsfjall volcanic system?

The differences in crustal assimilation between the 2021 and 2022 eruptions of the Fagradalsfjall volcanic system have significant implications for its long-term evolution and behavior. The presence of extensive crustal contamination in the 2021 lavas, followed by a lack of contamination in the 2022 lavas, suggests dynamic changes in the magmatic processes and conduit systems feeding the eruptions. The initiation of the 2021 eruption involved pre-eruptive stalling, fractional crystallization, and crustal assimilation, indicating a complex magma plumbing system. In contrast, the 2022 lavas show no evidence of contamination, indicating a more efficient magma transit to the surface without significant crustal interactions. These differences imply variations in magma storage, ascent rates, and eruption dynamics within the volcanic system. Understanding these variations in crustal assimilation can provide insights into the evolution of the Fagradalsfjall volcanic system, its eruptive behavior, and the potential hazards associated with future eruptions.