Jökull - 01.01.2017, Page 35

Svavarsdóttir et al.
Figure 6. 208Pb/204Pb vs. 206Pb/204Pb isotopic variation: (a) samples reported in this study, (b) Bárðarbunga
basement rocks and other volcanic units north of Vatnajökull and (c) the Bárðardalur region. Grey points dis-
played on all graphs denote published data from Bárðarbunga and the NRZ (Thirlwall, 2004; Kokfelt et al.,
2006; Halldórsson et al., 2008; Peate et al., 2010; Kuritani et al., 2011; Pernet-Fisher, 2012; Sims et al.,
2013; Manning and Thirlwall, 2014). Error bars are smaller than the size of the symbols. WR: whole rock;
GR: groundmass. – 208Pb/204Pb á móti 206Pb/204Pb fyrir: (a) sýni sem greind voru í þessari rannsókn (b)
berggrunn Bárðarbungu og aðrar goseiningar norðan Vatnajökuls og (c) hraun Bárðardals. Áður birt gögn frá
Norðurgosbeltinu og Bárðarbungu eru merkt með gráum punktum.
mined in this study relative to the ratios reported by
Sigmarsson and Halldórsson (2015) (0.51306). How-
ever, such difference is also evident in Hf isotopes
(Figure 5f), suggesting some heterogeneity in the
Frambruni lava.
Lead isotope compositions were measured in ten
samples from the Bárðardalur region (Figure 6, Ta-
ble 2). Generally, Pb-isotopic ratios of the lava flows
from Bárðardalur are in good agreement with previ-
ously published data from the NRZ and Bárðarbunga.
Again, this also applies to 207Pb/204Pb ratios for these
samples (not shown here, but see details in Svavars-
dóttir, 2017). We note that four samples (B15–01,
B15–02, B15–09, B15–16) display slightly elevated
208Pb/204Pb ratios (38.15–38.21), while other sam-
ples collected from Bárðardalur valley lie within the
208Pb/204Pb range of 38.00–38.10. The elevated val-
ues are, however, compatible with the 208Pb/204Pb ra-
tios of Þjórsárhraun lava (38.15–38.17) reported by
Halldórsson et al. (2008) and other Bárðarbunga prod-
ucts reported by Manning and Thirlwall (2014).
30 JÖKULL No. 67, 2017