Melt inclusion constraints on the magma source of Eyjafjallajökull 2010 flank eruption

The 2010 eruptive activity at the Eyjafjallajökull volcanic system began 20 March with a basaltic flank eruption on a 300 m long fissure on the Fimmvruhls Pass, in between Eyjafjallajökull and Mrdalsjkull volcanoes. The magma expelled from the fissure is olivine- and plagioclase-bearing mildly alkali basalt that exhibits uniform and rather primitive whole-rock composition. This event provides a rare opportunity to assess deep magmatic processes in Iceland. Melt inclusions (MIs) hosted in olivine phenocrysts were analyzed for their major, trace and volatile element concentrations to enable identification of magmatic source(s) for Eyjafjallajökull volcano and to better constrain processes occurring at depth. The MIs, in particular those in Mg-rich olivines, record primary magma composition before homogenisation and differentiation during magma ascent. The olivine phenocrysts hosting the MIs have a large compositional range, extending from Fo₇₃ to Fo₈₇, reflecting changes in the magma characteristics from the source to the surface. The MI compositions exhibit significant variations with MgO ranging from 5.2 to 7.2 wt%. This compositional range was caused by a binary mixing of two basaltic end-members followed by fractional crystallization process. The sources of these end-members are identical to those of Katla and Surtsey basalts, with a dominant role of the Katla source. Trace element characteristics of the Fimmvruhls MIs suggest important proportions of recycled oceanic crust in their mantle sources.