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.