Compositional Characteristics and Spatial Distribution of Enriched Icelandic Mantle Components

• Published in: Journal of Petrology
• Main Authors: Peate, David W., Breddam, Kresten, Baker, Joel A., Kurz, Mark D., Barker, Abigail K., Prestvik, Tore, Grassineau, Nathalie, Skovgaard, Anna Cecilie
• Format: Text
• Language: English
• Published: Oxford University Press 2010
• Subjects: Original Papers; Reykjanes; Vestmannaeyjar; Snæfell; Iceland
• Online Access: http://petrology.oxfordjournals.org/cgi/content/short/51/7/1447; https://doi.org/10.1093/petrology/egq025

We present compositional data on a suite of 18 primitive neovolcanic alkali basalts from three flank-zone regions in Iceland (Vestmannaeyjar in the south, Snæfell in the east, and Snæfellsnes in the west) that are peripheral to the main rift zones that are dominated by tholeiitic basalts. This study integrates He isotope data with radiogenic isotope data (Sr–Nd–Pb–Hf), stable isotope data (δ18O), and trace element data to characterize the compositional features of the trace element enriched components of the Icelandic mantle. We also present high-precision Pb isotope data on an additional 57 lava samples from the flank zones (including Öræfajökull in the SE) and the Northern and Eastern rift zones. Most Icelandic lavas have negative Δ207Pb (–4 to –1), with higher values (–1 to +4) found only in samples from Öræfajökull, Snæfell, and parts of the Reykjanes Peninsula. At Snæfell, this EM1-type component is characterized by a low δ18O olivine signature (+4·1‰ to +4·6‰), moderate 206Pb/204Pb values (18·4–18·6) and mid-ocean ridge basalt (MORB)-like 3He/4He (6·9–7·5 R/R A ). Samples from Vestmannaeyjar and Snæfellsnes have mantle-like δ18O olivine (+4·9‰ to +5·0‰), and radiogenic 206Pb/204Pb values (18·9–19·3) that fall on the Northern Hemisphere Reference Line for 208Pb/204Pb (Δ208Pb –5 to +5). Compared with the Vestmannaeyjar lavas, Snæfellsnes lavas have higher La/Yb N (5–11 vs 3–5), lower ε Nd (5·5–6·5 vs 6·8–7·6) and lower 3He/4He (6·3–8·6 R/R A vs 11·4–13·5 R/R A ). Therefore, the most trace element enriched components in the Icelandic mantle are not the carriers of the high 3He/4He values (>15 R/R A ) found in some lavas on Iceland and the adjacent ridges, and instead are consistent with degassed, recycled components. Even after excluding the EM1-type high Δ207Pb samples, high-precision Pb isotope data produce a kinked array on a 206Pb/204Pb vs 208Pb/204Pb plot, which is not consistent with simple binary mixing between two end-members. This requires significant lateral heterogeneity within the Icelandic ...