The peculiar geochemical signatures of Sao Miguel (Azores) lavas: Metasomatised or recycled mantle sources?

Beier, C., Stracke, A. and Haase, K. (2007) The peculiar geochemical signatures of Sao Miguel (Azores) lavas: Metasomatised or recycled mantle sources? Earth and Planetary Science Letters, 259 (1-2). pp. 186-199. DOI 10.1016/j.epsl.2007.04.038.

Full text not available from this repository.

Supplementary data:


The island of Sao Miguel, Azores consists of four large volcanic systems that exhibit a large systematic intra-island Sr-Nd-Pb-Hf isotope and trace element variability. The westenmost Sete Cidades volcano has moderately enriched Sr-Nd-Pb-Hf isotope ratios. In contrast, lavas from the easternmost Nordeste volcano have unusually high Sr and Pb and low Nd and Hf isotope ratios suggesting a long-term evolution with high Rb/Sr, U/Pb, Th/Pb, Th/TJ and low Sm/Nd and Lu/Hf parent-daughter ratios. They have trace element concentrations similar to those of the HIMU islands, with the exception of notably higher alkali element (Cs, Rb, K, Ba) and Th concentrations. The time-integrated parent-daughter element evolution of both the Sete Cidades and Nordeste source matches the incompatibility sequence commonly observed during mantle melting and consequently suggests that the mantle source enrichment is caused by a basaltic melt, either as a metasomatic agent or as recycled oceanic crust. Our calculations show that a metasomatic model involving a small degree basaltic melt is able to explain the isotopic enrichment but, invariably, produces far too enriched trace element signatures. We therefore favour a simple recycling model. The trace element and isotopic signatures of the Sete Cidades lavas are consistent with the presence of ancient recycled oceanic crust that has experienced some Pb loss during sub-are alteration. The coherent correlation of the parent-daughter ratios (e.g. Rb/Sr, Th/U, U/Pb) and incompatible element ratios (e.g. Nb/Zr, Ba/Rb, La/Nb) with the isotope ratios in lavas from the entire island suggest that the Sete Cidades and Nordeste source share a similar genetic origin. The more enriched trace element and isotopic variations of Nordeste can be reproduced by recycled oceanic crust in the Nordeste source that contains small amounts of evolved lavas (similar to 1-2%), possibly from a subducted seamount. The rare occurrence of enriched source signatures comparable to Nordeste may be taken as circumstantial evidence that stirring processes in the Earth's mantle are not able to homogenise material within the size of seamounts over timescales of mantle recycling. (c) 2007 Elsevier B.V. All rights reserved.

Document Type: Article
Keywords: enriched mantle radiogenic isotopes incompatible elements subduction recycling Ocean Island Basalts trace-element geochemistry young pacific seamounts eastern galapagos rift os isotope systematics oceanic island basalts enriched mantle peridotite xenoliths continental-crust inca transform plume sources
Research affiliation: Kiel University
DOI etc.: 10.1016/j.epsl.2007.04.038
ISSN: 0012-821X
Date Deposited: 12 Jan 2012 06:03
Last Modified: 08 Oct 2012 10:20

Actions (login required)

View Item View Item