Walowski, KJ, Kirstein, LA, De Hoog, JCM et al. (4 more authors) (2019) Investigating ocean island mantle source heterogeneity with boron isotopes in melt inclusions. Earth and Planetary Science Letters, 508. pp. 97-108. ISSN 0012-821X
Abstract
Recycling of the lithosphere via subduction drives the trace element and isotopic heterogeneity of the mantle, yet, the inventory of volatile elements in the diverse array of mantle reservoirs sampled at ocean islands remains uncertain. Boron is an ideal tracer of volatile recycling because it behaves similarly to volatiles during high-temperature geochemical reactions and carries a distinctive isotope signature into the mantle, but is subsequently little-influenced by degassing on return to the surface. Furthermore, B-rich recycled lithologies will have a strong influence on typical upper mantle compositions characterized by low B concentrations (<0.2 μg/g and δ11B −7.1 ± 0.9‰). Here, we present and compare the B abundances and isotope compositions, together with the volatile element contents (H₂O, CO₂, and Cl) of basaltic glasses and olivine-hosted melt inclusions from two different ocean island localities (La Palma, Canary Islands, and Piton de Caille, La Réunion Island). Our results suggest that olivine hosted melt inclusions are protected from contamination during ascent and provide more robust estimates of primary mantle source δ11B than previous bulk rock studies. We find that the δ11B of the La Réunion samples (−7.9 ± 0.5‰ (2σ)) overlaps with the recently defined MORB datum, indicating that the depleted upper-mantle and ‘primitive mantle’ reservoirs are indistinguishable with respect to δ11B, or that B concentrations are sufficiently low that they are diluted by partial melting in the uppermost mantle. In contrast, the La Palma samples, notable for their radiogenic Pb isotope ratios, are characterized by δ11B values that are distinctly isotopically lighter (−10.5 ± 0.7‰ (2σ)) than La Réunion or MORB. We suggest these isotopically light values are derived from significantly dehydrated recycled materials preserved in the La Palma mantle source region, in keeping with their lower B/Zr and H₂O/Ce. This work therefore provides strong new support for subduction zone processing as a mechanism for generating radiogenic Pb isotopic signatures and volatiles heterogeneities in the mantle.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2018 Elsevier B.V. This is an author produced version of a paper published in Earth and Planetary Science Letters. Uploaded in accordance with the publisher's self-archiving policy. |
Keywords: | ocean island basalts; mantle volatiles; mantle geochemistry; boron isotopes; melt inclusions; isotope geochemistry |
Dates: |
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Institution: | The University of Leeds |
Academic Units: | The University of Leeds > Faculty of Environment (Leeds) > School of Earth and Environment (Leeds) > Inst of Geophysics and Tectonics (IGT) (Leeds) |
Depositing User: | Symplectic Publications |
Date Deposited: | 20 Feb 2019 14:35 |
Last Modified: | 07 Jan 2020 01:39 |
Status: | Published |
Publisher: | Elsevier |
Identification Number: | 10.1016/j.epsl.2018.12.005 |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:142779 |
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