Diverse mantle components with invariant oxygen isotopes in the 2021 Fagradalsfjall eruption, Iceland

The basalts of the 2021 Fagradalsfjall eruption were the first erupted on the Reykjanes Peninsula in 781 years and offer a unique opportunity to determine the composition of the mantle underlying Iceland, in particular its oxygen isotope composition (delta O-18 values). The basalts show compositional variations in Zr/Y, Nb/Zr and Nb/Y values that span roughly half of the previously described range for Icelandic basaltic magmas and signal involvement of Icelandic plume (OIB) and Enriched Mid-Ocean Ridge Basalt (EMORB) in magma genesis. Here we show that Fagradalsfjall delta O-18 values are invariable (mean delta O-18 = 5.4 +/- 0.3 parts per thousand 2 SD, N = 47) and indistinguishable from normal upper mantle, in contrast to significantly lower delta O-18 values reported for erupted materials elsewhere in Iceland (e.g., the 2014-2015 eruption at Holuhraun, Central Iceland). Thus, despite differing trace element characteristics, the melts that supplied the Fagradalsfjall eruption show no evidence for O-18-depleted mantle or interaction with low-delta O-18 crust and may therefore represent a useful mantle reference value in this part of the Icelandic plume system. The 2021 eruption in the Reykjanes Peninsula of Iceland was the first in 800 years and was supplied by melts from diverse mantle source domains with near-identical oxygen isotope ratios, providing a unique insight into the Icelandic mantle plume.

Automated summary

The basalts erupted in the 2021 Fagradalsfjall eruption on the Reykjanes Peninsula offer a unique opportunity to study the composition of the mantle underlying Iceland. The oxygen isotope composition of these basalts is indistinguishable from the normal upper mantle, providing valuable insights into the Icelandic mantle plume.