Origin of gabbro and anorthosite mineral clusters in Fagradalsfjall lavas

The 2021 Fagradalsfjall lava brought a number of mineral clusters/xenoliths <6cm in diameter to the surface. Of the >40 samples collected from the field, eight xenoliths and one plagioclase megacryst were analyzed by stereo- and petrographic microscopes and the electron microprobe. In hand specimen, the xenoliths were sub-rounded to rounded, and were olivine and clinopyroxene bearing anorthositic gabbros and anorthosites. During thin section characterization, deformed and undeformed textural types were distinguished. In deformed xenoliths, deformation textures such as undulose extinction, deformed albite twinning, and triple junctions were observed in plagioclases. Plagioclase in deformed samples was typically unzoned and had bimodal crystal size distribution. Olivines had normal zoning where they were in contact with interstitial melt and more pronounced zoning was observed on the edges on the clusters. Undeformed samples did not show deformation features and had ophitic and poikilitic texture. Clinopyroxene in undeformed xenoliths was commonly observed interstitially as well as discrete subhedral crystals. The interstitial clinopyroxene resorbed the edges of plagioclase and olivine and had uniform extinction in all but one sample. 
Electron microprobe results show that the compositional variation of minerals within the xenoliths overlaps and exceeds the compositional variation of the host lava macrocryst cargo. Olivine forsterite, plag anorthite, Cpx Mg#, and Cr# content ranged from 80-89, 76-89, 82-87, and 6-18, respectively in mineral cores and 59-86, 65-86, 71-87, and 0.4-12, respectively, in zoned rims. Mineral compositions overlap in both deformed and undeformed samples. In general, undeformed samples cover a broader range compared to deformed ones, the latter being much more uniformly primitive. One deformed sample is an outlier with significantly lower forsterite (~73-79), anorthite (~66-71), and Mg# (~74) in clinopyroxene compared to the rest of the clusters and lava phenocrysts.
Plagioclases in most xenoliths contained devitrified silicate melt inclusions. Melt compositions after post entrapment corrections are in equilibrium with their host plagioclases according to Putirka (2008). The calculated temperatures based on plagioclase melt pairs indicate a difference in crystallization environment between the clusters that overlap the lava phenocrysts and the evolved outlier. The average crystallization temperatures for most xenoliths is 1222°C, whereas for the deformed one is 1191°C, respectively. With an error of ±23°C, these two temperatures could be from separate sources.