Petrological intrepretation of the 2010 Eyjafjallajökull flank basaltic eruption

Geophysical data from Eyjafjajökull volcano has shown how magma ascent is the key in triggering the March 2010 eruption (Sigmudson et al., 2010, Nature 468, 426-430). This process has been documented through mineral phase equilibria, which have been used to get petrological interpretations of the eruptive and pre-eruptive conditions. Basaltic scorias from the Fimmvörduháls flank eruption have been collected and studied with the purpose of constraining mineral-melt associations relating to changes in the intensity of parameters during magma ascending. Special observations to the major element composition of glass inclusions and composition of the groundmass have been taken into account. Plagioclase exhibits sieve texture containing evolved liquid inclusions. Scoria composition is compared with MELTS code calculations. An anomalous fractionation pattern is characterized by a continuous increase in Ti with ongoing fractionation; this is not what is expected in tholeiitic systems. The analyzed melt inclusions follow a continuous increasing trend reaching values of approximately TiO2=5 wt% for MgO=2.5 wt% and TiO2=10 wt% for the most evolved melts which have a matrix of MgO<2 wt%. This behavior of Ti, as an incompatible element for low MgO contents, indicates very low pressure of fractionation (lower than 1 kbar) in a system buffered around QFM conditions. Clinopyroxene exhibits an oscillatory pattern with resorption zones corresponding to the Cr-Ti-Al rich rims; these are interpreted as changes in intensity of parameters during magma ascent. Experiments with the scoria were carried out to reproduce mineralogical and textural associations according to previous calculated pre-eruptive conditions. The combined study of mineral composition, phase assemblages, liquid trend evolution and experiments on the reproduction of mineralogical and textural associations can define pre-eruptive conditions and possible magma replenishment prior to eruption.