On the iron isotope heterogeneity of lithospheric mantle xenoliths

Implications for mantle metasomatism, the origin of basalts and the iron isotope composition of the Earth

Franck Poitrasson*, Guillaume Delpech, Michel Grégoire

*Corresponding author for this work

Research output: Contribution to journalArticle

48 Citations (Scopus)

Abstract

With the aim to better understand the cause of the iron isotope heterogeneity of mantle-derived bulk peridotites, we compared the petrological, geochemical and iron isotope composition of four xenolith suites from different geodynamic settings; sub-arc mantle (Patagonia); subcontinental lithospheric mantle (Cameroon), oceanic mantle (Kerguelen) and cratonic mantle (South Africa). Although correlations were not easy to obtain and remain scattered because these rocks record successive geological events, those found between δ57Fe, Mg#, some major and trace element contents of rocks and minerals highlight the processes responsible for the Fe isotope heterogeneity. While partial melting processes only account for moderate Fe isotope variations in the mantle (<0.2 ‰, with bulk rock values yielding a range of δ57Fe ± 0.1 ‰ relative to IRMM-14), the main cause of Fe isotope heterogeneity is metasomatism (>0.9 ‰). The kinetic nature of rapid metasomatic exchanges between low viscosity melts/fluids and their wall-rocks peridotite in the mantle is the likely explanation for this large range. There are a variety of responses of Fe isotope signatures depending on the nature of the metasomatic processes, allowing for a more detailed study of metasomatism in the mantle with Fe isotopes. The current database on the iron isotope composition of peridotite xenoliths and mafic eruptive rocks highlights that most basalts have their main source deeper than the lithospheric mantle. Finally, it is concluded that due to a complex geological history, Fe isotope compositions of mantle xenoliths are too scattered to define a mean isotopic composition with enough accuracy to assess whether the bulk silicate Earth has a mean δ57Fe that is chondritic, or if it is ~0.1 ‰ above chondrites as initially proposed.

Original languageEnglish
Pages (from-to)1243-1258
Number of pages16
JournalContributions to Mineralogy and Petrology
Volume165
Issue number6
DOIs
Publication statusPublished - Jun 2013
Externally publishedYes

Keywords

  • Iron isotopes
  • Mantle peridotites
  • Melt extraction
  • Metasomatism

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