Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume

Bruce F. Schaefer, Simon Turner*, Ian Parkinson, Nick Rogers, Chris Hawkesworth

*Corresponding author for this work

Research output: Contribution to journalArticle

74 Citations (Scopus)

Abstract

The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection1,2. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios - lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.

Original languageEnglish
Pages (from-to)304-307
Number of pages4
JournalNature
Volume420
Issue number6913
DOIs
Publication statusPublished - 21 Nov 2002
Externally publishedYes

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