Oxygen isotope evidence for the origin of chemical variations in lavas from Theistareykir volcano in Iceland's northern volcanic zone

• Published in: Earth and Planetary Science Letters
• Main Authors: Eiler, John M., Grönvold, Karl, Kitchen, Nami
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2000
• Subjects: Iceland; Icelandic plume; lava; oxygen; isotope ratios; magma contamination; Elliott
• Online Access: https://doi.org/10.1016/S0012-821X(00)00318-6

Oxygen isotope ratios in phenocrysts from recent Theistareykir lavas (Iceland) are consistently ^(18)O-depleted relative to common terrestrial basalts (e.g. δ^(18)O olivine=4.7–4.1‰) and correlate with geochemical indices of 'enrichment' (e.g. K_2O/TiO_2; La/Sm) and major element indices of differentiation (e.g. Mg#; CaO/Na_2O). The sense of these correlations is that decreasing δ^(18)O is accompanied by increasing 'enriched' geochemical signatures and an increasing extent of differentiation. These trends are similar to (although more subtle than) those defined by highly differentiated and contaminated Icelandic andesites, dacites and rhyolites. The trends we observe are consistent with models in which primary recent Theistareykir magmas are highly 'depleted' in their incompatible element geochemistry and similar in δ^(18)O to common terrestrial basalts; differentiation of these magmas is accompanied by contamination by the low δ^(18)O, and on average more 'enriched' rocks of the Icelandic crust to produce the observed spectrum in δ^(18)O and other geochemical indices. Our results suggest that geochemical variations among recent Theistareykir lavas are only indirect constraints on the composition and dynamics of the Iceland plume. Extrapolation of the geochemical trends we observe to oxygen isotope compositions within the range of common oceanic basalts suggests that primary recent Theistareykir magmas are exceptionally depleted (e.g. La/Sm=0.2–0.5), indicating unusually high degrees and/or multiple stages of melting of their sources. © 2000 Elsevier Science B.V. Received 13 June 2000; received in revised form 17 October 2000; accepted 20 October 2000. We thank P. Asimow, T. Elliott and E. Stolper for their insightful comments on an early draft of this work, J. Blichert-Toft, A. Stracke and A. Zindler for sharing unpublished data for the samples we have examined, and T. Elliott, T. Kogiso and an anonymous reviewer for their thorough reviews of this paper. Finally, we particularly thank D. McKenzie ...