A preliminary assessment of the symmetry of source composition and melting dynamics across the Azores plume

Christoph Beier*, Simon Turner, Terry Plank, William White

*Corresponding author for this work

Research output: Contribution to journalArticle

33 Citations (Scopus)

Abstract

In order to undertake a preliminary assessment of the extent of symmetry in source composition and melting dynamics in the Azores plume we present new ICP-MS trace element data along with Sr, Nd, Pb, and U-Th-Ra isotope data for samples from the islands Flores and Corvo west of the Mid-Atlantic Ridge. We also present data from a picrite from Faial and new ICP-MS trace element data for 28 basaltic lavas from the eastern Azores Plateau to augment data published previously from these samples. Rare earth element data for primitive lavas (MgO ≥ 5% and Mg # ≥ 60) have La/YbN ∼ 10 and variable Ce and/or Eu anomalies. Multi-incompatible trace element patterns normalized to primitive mantle are convex upward with small negative Th and K ± Pb anomalies. While lavas to the east are characterized by low Nb/Zr and generally lower La/Yb ratios (with the notable exception of eastern So Miguel), lavas from the western islands have slightly higher Nb/Zr and La/Yb inferred to reflect smaller degrees of partial melting. The Sr-Nd-Pb isotope systematics imply that Corvo and Flores sample components which range from an isotopic source commonly found in the Azores (e.g., at the eastern island of Graciosa) to a more depleted, MORB-like mantle sampled at the Mid-Atlantic Ridge. However, in common with uncontaminated samples from São Miguel, the Corvo and Flores samples appear to have slightly lower 230Th excesses and higher La/Yb, Tb/Yb than the other Azores islands or the Mid-Atlantic Ridge samples. The trace element and isotope data indicate a relatively symmetric pattern with distance across the MAR, while U-Th disequilibria, and thus inferred melting dynamics, appear less symmetric. Nevertheless, the data suggest that heterogeneities in source composition do not have a large effect on melting dynamics, at least within the Azores islands.

Original languageEnglish
Article numberQ02004
Pages (from-to)Q02004-1-Q02004-14
Number of pages14
JournalGeochemistry, Geophysics, Geosystems
Volume11
Issue number2
DOIs
Publication statusPublished - Feb 2010

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