Calibration of an Empirical Thermometer and Oxybarometer based on the Partitioning of Sc, Y and V between Olivine and Silicate Melt

Mallmann, Guilherme and O'Neill, Hugh St C. (2013) Calibration of an Empirical Thermometer and Oxybarometer based on the Partitioning of Sc, Y and V between Olivine and Silicate Melt. Journal of Petrology, 54 5: 933-949. doi:10.1093/petrology/egt001


Author Mallmann, Guilherme
O'Neill, Hugh St C.
Title Calibration of an Empirical Thermometer and Oxybarometer based on the Partitioning of Sc, Y and V between Olivine and Silicate Melt
Journal name Journal of Petrology   Check publisher's open access policy
ISSN 0022-3530
1460-2415
Publication date 2013-05-01
Year available 2013
Sub-type Article (original research)
DOI 10.1093/petrology/egt001
Volume 54
Issue 5
Start page 933
End page 949
Total pages 17
Place of publication Oxford, United Kingdom
Publisher Oxford University Press
Language eng
Formatted abstract
The evolution of basaltic magmas depends on their redox state, hence oxygen fugacity, but there is increasing evidence that this intensive thermodynamic variable may be less well understood in basalts than commonly supposed. The redox state of terrestrial basalts has to a large extent been inferred from the Fe3+/Fe2+ ratios of their quenched glasses. However, this quantity appears to be significantly affected during late and post-eruptive processes in magmatic systems (e.g. by degassing, charge-transfer reactions of redox-variable species, and alteration), so that the degree to which the Fe3+/Fe2+ ratios preserved in basaltic glasses reflect the oxidation state of the magma at high temperature is unclear. Because olivine is the first silicate mineral to crystallize from primitive basaltic liquids on cooling following decompression, the equilibrium partitioning relations preserved in olivine phenocrysts in basalts are, in principle, less disturbed by these late and post-eruptive processes and, therefore, may better reflect the high-temperature (pre-eruptive) conditions of the magma. Here we calibrate an oxybarometer based on the strong sensitivity of the partitioning of vanadium between olivine and silicate melt to oxygen fugacity. Our empirical parameterization, calibrated over a range of redox conditions between four log10 units above and below the quartz–fayalite–magnetite (QFM) oxygen buffer, takes into account the effects of temperature, olivine composition (i.e. Mg/Fe ratios) and melt composition (namely the activities of CaO, SiO2, AlO1·5, NaO0·5 and KO0·5), and allows oxygen fugacity determinations to within ∼0·25 log10 units. We also explore the sensitivity of the exchange partitioning of Sc and Y between olivine and melt to temperature as a geothermometer. Our calibration indicates that this geothermometer allows temperature to be estimated to within 15°C, but precision is strongly dependent on the Sc and Y measurements in olivine and melt.
Keyword Olivine
Basalt
Temperature
Oxygen fugacity
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status Non-UQ

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