Magma sources at Eyjafjöll and adjacent South Iceland central volcanoes

We present Pb-Sr-Nd-Hf-O isotopic data for Quaternary
transitional basaltic rocks of the six central volcanoes of the
South Iceland flank zone. These are amongst the deepest melts
in Iceland based on high Dy/Yb and low Na2O/TiO2. Each
volcano shows limited ranges in isotopic composition, but
Eyjafjöll Sr-Nd-Hf-O data lie systematically between
Heimaey at more depleted isotopic compositions to the SW,
and Katla and Tindfjöll at more enriched compositions to the
E and N respectively. A tight 143Nd/144Nd – "18Ool correlation
at Eyjafjöll extends from the mantle-like "18O of Heimaey to
+4.2‰ values in Katla and Hekla olivines. Detail provided by
double-spike Pb data shows however that Katla eruptives are
not a possible enriched mixing end-member as they have
relatively elevated 208Pb, and indeed 3 or more mixing
components would be required to explain the Pb isoopic
compositions of Eyjafjöll and Tindfjöll eruptives.
The Nd-O isotopic correlation at Eyjafjöll is present in
samples from several interglacial stages and could only result
from crustal contamination if Eyjafjöll was underlain by an
early Quaternary basement of hydrothermally-altered Katlalike
volcanics. Given that the bulk of Katla has developed
more recently than Eyjafjöll, this seems implausible. The
+4.2‰ olivine "18O observed at Katla, Hekla, and in some
Tindfjöll and Eyjafjöll lavas, is consistent with the value
proposed in Icelandic low-"18O mantle [1]. It is associated also
with low K/Nb and low Na2O/TiO2 suggesting that it is cohosted
with recycled oceanic crust that in the flank zone is
most effectively tapped by deep melts.