title: Experimental partitioning of halogens and other trace elements between olivine, pyroxenes, amphibole and aqueous fluid at 2 GPa and 900-1,300 °C.
abstract: We present new partition coefficients for various trace elements including Cl between olivine, pyroxenes, amphibole and coexisting chlorine-bearing aqueous fluid in a series of high-pressure experiments at 2 GPa between 900 and 1,300 °C in natural and synthetic systems. Diamond aggregates were added to the experimental capsule set-up in order to separate the fluid from the solid residue and enable in situ analysis of the quenched solute by LA-ICP-MS. The chlorine and fluorine contents in mantle minerals were measured by electron microprobe, and the nature of OH defects was investigated by infrared spectroscopy. Furthermore, a fluorine-rich olivine from one selected sample was investigated by TEM. Results reveal average Cl concentrations in olivine and pyroxenes around 20 ppm and up to 900 ppm F in olivine, making olivine an important repository of halogens in the mantle. Chlorine is always incompatible with Cl partition coefficientsDClolivine/fluidvarying between 10-5and 10-3, whereasDClorthopyroxene/fluidandDClclinopyroxene/fluidare ~10-4andDClamphibole/fluidis ~5 × 10-3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered asDamph/fluid≈Dcpx/fluid>Dopx/fluid>Dol/fluidbut thatDmineral/fluidfor Li and P is very similar for all observed silicate phases. Infrared spectra of olivine synthesized in a F-free Ti-bearing system show absorption bands at 3,525 and ~3,570 cm-1. In F ± TiO2-bearing systems, additional absorption bands appear at ~3,535, ~3,595, 3,640 and 3,670 cm-1. Absorption bands at ~3,530 and ~3,570 cm-1, previously assigned to humite-like point defects, profit from low synthesis temperatures and the presence of F. The presence of planar defects could not be proved by TEM investigations, but dislocations in the olivine lattice were observed and are suggested to be an important site for halogen incorporation in olivine.
authors.affiliation: Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52f, 6020 Innsbruck, Austria.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Fabbrizio
authors.affiliation: Institute of Mineralogy and Petrography, University of Innsbruck, Innrain 52f, 6020 Innsbruck, Austria.
authors.forename: Roland
authors.initials: R
authors.lastname: Stalder
authors.affiliation: Lab of Inorganic Chemistry, ETH Zürich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Hametner
authors.affiliation: Lab of Inorganic Chemistry, ETH Zürich, Wolfgang-Pauli-Str. 10, 8093 Zurich, Switzerland.
authors.forename: Detlef
authors.initials: D
authors.lastname: Günther
authors.affiliation: Deutsches GeoForschungsZentrum, Section 3.3, Telegrafenberg, 14473 Potsdam, Germany.
authors.forename: Katharina
authors.initials: K
authors.lastname: Marquardt
keywords: Defects; Halogens; Mantle; TEM; Trace element partitioning