Fig. 7: Schematic model.

a Sketch placing Fagradalsfjall (F) in a regional context in relation to the Reykjanes Volcanic Belt (RVB), the Western Volcanic Zone (WVZ), and the Eastern Volcanic Zone (EVZ) of Iceland (see Fig. 1 for map view of Iceland). b Close-up of Fagradalsfjall showing a heterogeneous “plum pudding” or “streaky” mantle comprising various source components such as EMORB, OIB, and DIP. Variable melts from this heterogeneous mantle were assembled in a lower crustal magma reservoir, which likely experienced multiple replenishment episodes leading to complex mineral zoning. Mixing of melts shortly before eruption facilitated preservation of compositional heterogeneities inherited from the mantle source. Remarkably, despite the variability in the compositions of Fagradalsfjall erupted products, their δ¹⁸O values are homogeneous at 5.4‰ on average with no evidence for low-δ¹⁸O mantle or interaction with low-δ¹⁸O crust. The mean δ¹⁸O value for Fagradalsfjall may thus represent a useful mantle reference in this part of the Iceland plume system. Abbreviations: B Bláfjöll, Br Brennisteinsfjöll, K Krýsuvík, MAR Mid-Atlantic Ridge, MORB Mid-Ocean Ridge Basalt, R Reykjanes, S Svartengi.