Insights into Li and Li isotope cycling and sub-arc metasomatism from veined mantle xenoliths, Kamchatka

Ralf Halama, Ivan P. Savov, Roberta L. Rudnick, William F. McDonough

Research output: Contribution to journalArticlepeer-review

66 Citations (Scopus)

Abstract

Harzburgitic xenoliths cut by pyroxenite veins from Avachinsky volcano, Kamchatka, are derived from the sub-arc mantle and record element transfer from the slab to the arc. Olivine and orthopyroxene in the harzburgites have Li isotopic compositions (δ7Li = +2.8 to +5.6) comparable to estimates of the upper mantle (δ7 Li ∼ +4 ± 2). The pyroxenite veins, which represent modal metasomatism and may therefore provide information about the metasomatic agent, have mantle-normalized trace element characteristics that suggest overprinting of their mantle source by an aqueous, slab-derived fluid. These include relative enrichments of Pb over Ce, U over Th and Sr over Nd. Li is enriched relative to the HREE, and ortho- and clinopyroxene from the veins are in Li elemental and isotopic equilibrium with each other and the surrounding harzburgite. Vein samples (δ7 Li = +3.0 to +5.0) do not record a significant slab-derived δ7Li signature. These observations can be reconciled if slab Li diffusively re-equilibrates in the mantle wedge. Modeling demonstrates that Li equilibration of small (1-2 cm width) veins or melt conduits is achieved at mantle wedge temperatures within 101- 105 years. We conclude that strongly fractionated Li isotopic signatures cannot be sustained for long periods in the sub-arc mantle, at least at shallow (<70 km) depths.

Original languageEnglish
Pages (from-to)197-222
Number of pages26
JournalContributions to Mineralogy and Petrology
Volume158
Issue number2
DOIs
Publication statusPublished - 2009 Feb 12
Externally publishedYes

Keywords

  • Kamchatka
  • Liisotopes
  • Lithium
  • Mantle xenoliths
  • Metasomatism
  • Sub-arc mantle

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology

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