Lower-to-mid crustal magma dynamics revealed by in-depth analyses of Sr and Nd isotope time-series of basalt erupted 2021-2024 on the Reykjanes Peninsula, Iceland.
Olgeir Sigmarsson 1,2, Alberto Caracciolo2, Edward W. Marshall2, Simon W. Matthews2, Enikö Bali2, Sæmundur A. Halldórsson2
Affiliations: 1Laboratoire Magmas et Volcans, CNRS-Université Clermont Auvergne-IRD, Aubière, France 2NorVolc, Institute of Earth Sciences, University of Iceland, Reykjavík, Iceland
Presentation type: Poster
Presentation time: Friday 16:30 - 18:00, Room Poster Hall
Poster Board Number: 16
Programme No: 1.5.23
Abstract
Seven short-lived basaltic fissure eruptions took place from December 2023 to December 2024 at the Sundhnúkur crater-row on the Svartsengi intra-transform spreading centre. The duration and magma volume of each eruption generally increased with time until the last event. The whole-rock major-element composition of the basalt produced is limited (with 7-8.5% MgO) whereas incompatible element and Sr-Nd isotope ratios vary (e.g. 87Sr/86Sr: 0.70312 - 0.70323 and 143Nd/144Nd: 0.51302-0.51295) irregularly with time (Matthews et al. 2024) until June 2024. Similar variability was observed for the isotope ratios during the six-months long 2021 eruption at Fagradalsfjall (87Sr/86Sr: 0.70310 - 0.70323 and 143Nd/144Nd: 0.51302-0.51295); Halldórsson et al., 2022; Marshall et al. 2024). An important difference is that the Sr isotope ratios are significantly higher for a given Nd isotope ratio in the 2024 Sundhnúkur basalt. Mass-balance criteria exclude significant crustal interaction and consequently, the two eruptions are fed from different deep-seated magma aggregation zones. The eruptions at Sundhnúkur crater-row all start as an intense but short-lived phase on several km long fissures reflecting pressure release in a magma chamber and consequent deflation. After June 2024, the Sr- and Nd isotope ratios and the incompatible element ratios reached the background values of the historical basalt lavas on the Reykjanes Peninsula. Therefore, the evacuation of the "enriched" (high 87Sr/86Sr and K2O/TiO2) basalt compositions, erupted from late April 2021, through 2022 and July 2023 in the Fagradalsfjall region and from December 2023 to June 2024 at Sundhnúkur, from the trans crustal magma domain may be over.