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The effect of liquid composition on the partitioning of Ni between olivine and silicate melt.

ABSTRACT: We report the results of experiments designed to separate the effects of temperature and pressure from liquid composition on the partitioning of Ni between olivine and liquid, [Formula: see text]. Experiments were performed from 1300 to 1600 °C and 1 atm to 3.0 GPa, using mid-ocean ridge basalt (MORB) glass surrounded by powdered olivine in graphite-Pt double capsules at high pressure and powdered MORB in crucibles fabricated from single crystals of San Carlos olivine at one atmosphere. In these experiments, pressure and temperature were varied in such a way that we produced a series of liquids, each with an approximately constant composition (~12, ~15, and ~21 wt% MgO). Previously, we used a similar approach to show that [Formula: see text] for a liquid with ~18 wt% MgO is a strong function of temperature. Combining the new data presented here with our previous results allows us to separate the effects of temperature from composition. We fit our data based on a Ni-Mg exchange reaction, which yields [Formula: see text] Each subset of constant composition experiments displays roughly the same temperature dependence of [Formula: see text] (i.e.,[Formula: see text]) as previously reported for liquids with ~18 wt% MgO. Fitting new data presented here (15 experiments) in conjunction with our 13 previously published experiments (those with ~18 wt% MgO in the silicate liquid) to the above expression gives [Formula: see text] = 3641 ± 396 (K) and [Formula: see text] = - 1.597 ± 0.229. Adding data from the literature yields [Formula: see text] = 4505 ± 196 (K) and [Formula: see text] = - 2.075 ± 0.120, a set of coefficients that leads to a predictive equation for [Formula: see text] applicable to a wide range of melt compositions. We use the results of our work to model the melting of peridotite beneath lithosphere of varying thickness and show that: (1) a positive correlation between NiO in magnesian olivine phenocrysts and lithospheric thickness is expected given a temperature-dependent [Formula: see text] and (2) the magnitude of the slope for natural samples is consistent with our experimentally determined temperature dependence. Alternative processes to generate the positive correlation between NiO in magnesian olivines and lithospheric thickness, such as the melting of olivine-free pyroxenite, are possible, but they are not required to explain the observed correlation of NiO concentration in initially crystallizing olivine with lithospheric thickness.

SUBMITTER: Matzen AK

PROVIDER: S-EPMC5165033 | biostudies-literature | 2017

REPOSITORIES: biostudies-literature

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The effect of liquid composition on the partitioning of Ni between olivine and silicate melt.

Matzen Andrew K AK Baker Michael B MB Beckett John R JR Wood Bernard J BJ Stolper Edward M EM

Contributions to mineralogy and petrology. Beitrage zur Mineralogie und Petrologie 20161219 1

We report the results of experiments designed to separate the effects of temperature and pressure from liquid composition on the partitioning of Ni between olivine and liquid, [Formula: see text]. Experiments were performed from 1300 to 1600 °C and 1 atm to 3.0 GPa, using mid-ocean ridge basalt (MORB) glass surrounded by powdered olivine in graphite-Pt double capsules at high pressure and powdered MORB in crucibles fabricated from single crystals of San Carlos olivine at one atmosphere. In these ...[more]

PMID: 28057942

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Project description: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 coefficients DClolivine/fluid varying between 10-5 and 10-3, whereas DClorthopyroxene/fluid and DClclinopyroxene/fluid are ~10-4 and DClamphibole/fluid is ~5 × 10-3. Furthermore, partitioning results for incompatible trace element show that compatibilities of trace elements are generally ordered as Damph/fluid ≈ Dcpx/fluid > Dopx/fluid > Dol/fluid but that Dmineral/fluid for 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.

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The effect of liquid composition on the partitioning of Ni between olivine and silicate melt.

Publications

The effect of liquid composition on the partitioning of Ni between olivine and silicate melt.

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