Publication Date:
2022-05-26
Description:
Author Posting. © The Authors, 2010. This is the author's version of the work. It is posted here by permission of Oxford University Press for personal use, not for redistribution. The definitive version was published in Journal of Petrology 51 (2010): 1447-1475, doi:10.1093/petrology/egq025.
Description:
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 characterise the compositional features of the trace-elementenriched
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 south-east) 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 characterised by a low δ18Oolivine
signature (+4.1‰ to +4.6‰), moderate 206Pb/204Pb values (18.4-18.6) and MORB-like 3He/4He
(6.9-7.5 R/RA). Samples from Vestmannaeyjar and Snæfellsnes have mantle-like δ18Oolivine
(+4.9‰ to +5.0‰), and radiogenic 206Pb/204Pb values (18.9-19.3) that fall on the NHRL for
208Pb/204Pb (Δ208Pb –5 to +5). Compared to the Vestmannaeyjar lavas, Snæfellsnes lavas have
higher La/YbN (5-11 vs. 3-5), lower εNd (5.5-6.5 vs. 6.8-7.6) and lower 3He/4He (6.3-8.6 R/RA vs.
11.4-13.5 R/RA). Therefore, the most trace element enriched components in the Icelandic mantle
are not the carriers of the high 3He/4He values (〉 15 R/RA) 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 an 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
mantle and the presence of more than just two compositionally-distinct local mixing end-member
components. Samples from each of the main axial rift zones define different trends. Despite the
tectonic continuity between the Northern Volcanic Zone and the Eastern Volcanic Zone, lavas
from these two rift zones define separate sub-parallel linear arrays. Lavas from the adjacent
Western Volcanic Zone and the Eastern Volcanic Zone define oblique linear arrays that converge
on a common local end-member that is not involved in the magmatism of the Northern Volcanic
Zone. Therefore, there is a distinct NE-SW compositional heterogeneity within the Icelandic
mantle.
Description:
work was funded primarily by the Danish National Research
Foundation through a grant to the former Danish Lithosphere Centre, with additional funding
from the University of Iowa for the oxygen isotope analyses.
Keywords:
Iceland
;
He isotopes
;
Pb isotopes
;
O isotopes
;
Flank zone lavas
;
Rift zone lavas
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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