Fig. 4. Conceptual model of melt extraction, accumulation, mixing and crustal ascent beneath Fagradalsfjall.
a, Melt storage pressures obtained by olivine-plagioclase-augite-melt (OPAM) barometry using compositions from glass, and MIs, clinopyroxene (cpx)–liquid barometry from crystal cores and rims, and the storage pressures consistent with the gas CO2/SO2 ratio, assuming closed-system degassing. The curves are kernel density estimates produced using a bandwidth based on the number of data points (Scott’s rule), which in all cases was greater than the measurement uncertainty. b, The lava erupted at the start of the eruption was depleted in composition, consistent with shallow, high-degree melting of a relatively depleted mantle source (yellow). However, as the eruption progressed, the melts became increasingly enriched, consistent with deeper, lower-degree partial melting of a more enriched mantle source (red). Note the reversed axis for La/Yb. c, A conceptual model of melt extraction, accumulation and crustal ascent beneath Fagradalsfjall. Melts are generated in the mantle and ascend to a near-Moho storage zone where crystallization, mixing and degassing occur before eruption. d, Evolution of a near-Moho reservoir that explains the erupted lava compositions at Fagradalsfjall. Initially, the magma reservoir contained depleted melt, but over the course of the eruption continuous recharge of enriched melt resulted in a compositional change within the magma reservoir.