Jökull - 01.01.2005, Blaðsíða 65

Holocene tephra stratigraphy and eruption frequency of Katla, S-Iceland
Figure 6. Basalt compositional fields for five indicated volcanic systems of the EVZ. Data from Jakobsson
(1979), Steinþórsson (1977), Vilmundardóttir (1977), Óskarsson et al., (1982), Grönvold and Jóhannesson
(1984), Steinþórsson et al., (1985), Sigmarsson et al., (1992) and Thordarson et al., (1996, 2001, 2003). The
data of this study is plotted as diamonds (Katla tephra) and as squares (other volcanic systems). – Graf sem
sýnir hlutfall járn- og títanoxíða á móti kísiloxíði fyrir fimm eldstöðvakerfi á Eystra gosbeltinu samkvæmt efna-
greiningum Sveins Jakobssonar (1979), Sigurðar Steinþórssonar (1977), Elsu Vilmundardóttur (1977), Níelsar
Óskarssonar og fl. (1982), Karls Grönvolds og Hauks Jóhannessonar (1984), Sigurðar Steinþórssonar og fl.
(1985), Olgeirs Sigmarssonar og fl. (1992), og Þorvaldar Þórðarsonar og fl. (1996, 2001, 2003). Bláir tíglar
sýna að efnagreiningum á forsögulegum og sögulegum Kötlugjóskulögum í þessu verkefni ber vel saman við
áður birt gögn. Ferningar sýna efnasamsetningu gjóskulaga frá öðrum eldstöðvakerfum.
ure 5 are the compositional fields of basalts from
the Hekla/Vatnafjöll, Veiðivötn and Grímsvötn vol-
canic systems. The Katla volcanic system products
are readily distinguished from that of the Grímsvötn
and Veiðivötn systems on element to element plots,
but such plots do not discriminate between the Fe-Ti
basalts from the Katla and Hekla/Vatnafjöll systems.
However, the products of these two systems are better
distinguished by their FeO/TiO2 value (Figure 6).
The discrimination plots indicate that out of the
108 prehistoric tephra layers that were analysed, 101
originated from the Katla volcanic system. The data
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