Petrogenesis of Silicic Magmas in Iceland through Space and Time: The Isotopic Record Preserved in Zircon and Whole Rocks

Magmatic Processes at Snæfell Volcano, Iceland, Constrained by Zircon Ages, Isotopes, and Trace Elements

“…Snaefell zircon ε Hf is higher than in basalts from other modern off-rift zones, including Öraefajökull (ε Hf ∼+11 to +12) and overlaps the range (ε Hf ∼+13.5 to +19) of values from basalts erupted from modern established rifts (Peate et al, 2010; data re-reduced using the CHUR value of Bouvier et al, 2008 to be internally consistent with this study). Measured zircon Hf compositions in samples IESn1, IESn2, and IESn3 vary by ∼2-2.5 epsilon units (Table 2; Figure 3c), which is typical for Icelandic systems (Banik et al, 2018;Carley et al, 2020;Padilla et al, 2016).…”

“…The correlation between ε Nd and ε Hf is generally strong globally (e.g., Vervoort & Blichert-Toft, 1999; ε Hf(t) = 1.36 ×ε Nd(t) + 3), which was demonstrated for Icelandic basalts by Peate et al (2010). Further, Carley et al (2020) demonstrated a correlation between Icelandic whole rock and zircon Hf isotope values, and then developed mathematical relationships to associate Icelandic whole rock Hf and Nd isotope values-ε Hf =(1.48 ×ε Nd ) + 2.52; r 2 = 0.65-and zircon Hf isotope compositions. Isotopic values for whole rocks may then be estimated in the absence of measured values using the above relationships.…”

“…Hafnium isotope compositions were obtained for 60 Snaefell zircon grains (Figure 3, Table 2). The ε Hf for Snaefell samples ranges from +13.3 to +17.8, which includes some of the highest individual ε Hf values observed in Icelandic zircon (e.g., Carley et al, 2020). Samples IESn1 and IESn2, which have nearly identical U-Pb ages and were collected in close proximity to one another, have weighted sample mean ε Hf of +14.1 ± 0.3 (2SE; MSWD = 2.3) and +14.2 ± 0.2 (MWSD = 1.3), respectively.…”

“…The data reported by Hards et al (2000), including the rhyolite, do not include Hf isotope compositions. We used published Nd isotope compositions and the calculation of Carley et al (2020), above, to determine approximate Hf isotope compositions for a sample of rhyolite and additional basalt samples. We do not observe the expected correlation between Snaefell whole rock rhyolite ε Nd (measured) and zircon ε Hf (measured) and between basalt ε Hf (calculated) and zircon ε Hf (measured) (Figure 7).…”

“…Whole rock and zircon ε Hf versus whole rock ε Nd for rhyolites from Snaefell and other Neovolcanic systems. Snaefell rhyolite and basalt from Hards et al (2000) with calculated ε Hf from measured ε Nd following the method of Carley et al (2020); Snaefell zircon from this study. Compositions from Snaefell basalts noted by the hatched field (Peate et al, 2010) and stars (Hards et al, 2000) for comparison.…”