The effect of oxygen fugacity on the partitioning of Re between crystals and silicate melt during mantle melting

Mallmann, G. and O'Neill, H.St.C. (2007) The effect of oxygen fugacity on the partitioning of Re between crystals and silicate melt during mantle melting. Geochimica et Cosmochimica Acta, 71 11: 2837-2857. doi:10.1016/j.gca.2007.03.028


Author Mallmann, G.
O'Neill, H.St.C.
Title The effect of oxygen fugacity on the partitioning of Re between crystals and silicate melt during mantle melting
Journal name Geochimica et Cosmochimica Acta   Check publisher's open access policy
ISSN 0016-7037
1872-9533
Publication date 2007-06-01
Sub-type Article (original research)
DOI 10.1016/j.gca.2007.03.028
Open Access Status
Volume 71
Issue 11
Start page 2837
End page 2857
Total pages 21
Place of publication Kidlington, Oxford, United Kingdom
Publisher Pergamon Press
Language eng
Subject 1906 Geochemistry and Petrology
Abstract Interpretation of Re-Os isotopic systematics applied to mantle and mantle-derived rocks is currently hindered by the poorly understood behaviour of Re and Os during partial melting. Of particular interest is the incompatibility of Re and how it partitions between melt and the different mantle phases. Here, we study the partitioning behaviour of Re between the common upper mantle minerals (garnet, spinel, clinopyroxene, orthopyroxene, and olivine) and silicate melt under temperature (1275-1450 °C) and pressure (1.5-3.2 GPa) conditions relevant for basaltic magma genesis, over a range of oxygen fugacity (f{hook}O2) large enough (QFM+5.6 to QFM-2.9) to demonstrate the effects of changing the oxidation state of Re from 4+ to 6+. Rhenium crystal/silicate-melt partition coefficients vary by 4-5 orders of magnitude, from moderately compatible to highly incompatible, for pyroxenes, garnet, and spinel as the oxidation state of Re changes from 4+ to 6+, but Re in either oxidation state is incompatible in olivine. Because the changeover from the one Re oxidation state to the other occurs over the range of f{hook}O2s pertinent to partial melting in the Earth's mantle, bulk Re crystal/silicate-melt partition coefficients during mantle melting are also expected to vary significantly according to the oxidation state of the system. For instance, assuming QFM-0.7 and QFM+1.6 as average f{hook}O2 for mid-ocean ridge (MORBs) and island arc (IABs) basalts, respectively, a difference of at least one order of magnitude for bulk Re partition coefficients is expected (excluding any influence from a sulphide phase). Hence, Re is probably much more incompatible during the genesis of IABs compared to MORBs. Our results also demonstrate that Re4+ has a partitioning behaviour similar to Ti4+ rather than Yb, and is accordingly not a sensitive indicator of garnet in the source. The lower concentrations of Re observed in ocean island basalts (OIBs) compared to MORBs are therefore not a result of being generated deeper in the mantle where garnet is stable, leaving the hypothesis of late-stage loss of Re from OIB lavas by degassing as the most plausible explanation.
Q-Index Code C1
Q-Index Status Provisional Code
Institutional Status Non-UQ

Document type: Journal Article
Sub-type: Article (original research)
Collection: School of Earth Sciences Publications
 
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