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

Halama, Ralf, Savov, Ivan P., Rudnick, Roberta L. and McDonough, William F. (2009) Insights into Li and Li isotope cycling and sub-arc metasomatism from veined mantle xenoliths, Kamchatka. Contributions to Mineralogy and Petrology, 158 (2). pp. 197-222. DOI 10.1007/s00410-009-0378-5.

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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 (δ7Li ~ +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 (δ7Li = +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.

Document Type: Article
Keywords: Volcanology; Lithium - Li isotopes - Sub-arc mantle - Mantle xenoliths - Metasomatism - Kamchatka
Research affiliation: OceanRep > SFB 574 > C1
OceanRep > SFB 574
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1007/s00410-009-0378-5
ISSN: 0010-7999
Contribution Number:
SFB 574159
Date Deposited: 13 Jul 2010 11:12
Last Modified: 21 Sep 2016 11:34

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