Geochemical analysis and develoment of the magma

Eruption of Eyjafjalla Volcano Eyjafjalla on April 2010

Geochemical analysis from Dipl.-Geol. Frank Möckel

Sampling of a five cm thick ash layer on the Solheimajökull glacier near Skogar at 20.4.2010 from Th. Boeckel.

Laboratory-analytic investigations (institutes OF Earth Sciences - Nordic Volcanological centre and own analyses) of pyroclastites at the Fimmvörduháls fissure eruption (flank of the Eyjafjallajökull volcano) and the large explosive eruption series within the range of the summit Caldera of the Eyjafjallajökull showed, that the promoted volcanic materials differ chemically clearly from each other. Both volcanic events on the same volcanic complex of the Eyjafjallajökull volcano took place, but different magmas were ejected. The results of the chemical rock investigations can be represented graphically very good in the TAS diagram. With the TAS diagramm it is to be determined relatively uncomplicatedly the possible content of SiO2 and the sum of Na2O + K2O in volcanic rocks.With the outbreak in the area of the Fimmvörduhals relatively primitive and a few differentiated alkali-olivine-basalts with SiO2 came up - contenting around approx. 47 weight % from larger depth to the eruption. With these alkali olivine basalts (AOB) the contents of Na2O are + to K2O with approx. 3.8 weight %. The Pyroclastite of the summit eruptions of the Eyjafjallajökull volcano has completely different chemical composition.Here contents of SiO2 were determined of on the average 57.7 weight %.   The contents of Na2O + K2O are with on the average 7.0 weight %. Thus this pyroclastite falls in field of the Trachyandesite (TrAn). This Trachyandesite is geochemical further developed compared with the primitive alkali olivine basalts. These chemical changes in the magma is explained through fractionate crystallization, strong fluida supply from the depth and other deviation processes. The Trachyandesite magma resulting from it is enriches at SiO2 and Na2O. Altogether incompatible elements enrich themselves such as Zr, SEE and Nb in the trachyandesitic melt. On the other hand the new magma, under the complex deviation procedures, contains much less TiO2, MgO, CaO and FeO. The lighter Trachyandesite magma collected itself in the upper section of the magma chamber directly underneath the volcanic vent. Further the trachyandesite magma is more gas-rich, substantially more strongly viscous and somewhat cool than alkali olivine output magma. For these reasons it is to mentioned that the eruptions of the trachyandesitic magma was strongly explosive in the summit range of the Eyjafjallajökull volcano.