Effect of water on the fluorine and chlorine partitioning behavior between olivine and silicate melt

Bastian Joachim; André Stechern; Thomas Ludwig; Jürgen Konzett; Alison Pawley; Lorraine Ruzié-Hamilton; Patricia L Clay; Ray Burgess; Christopher J Ballentine

doi:10.1007/s00410-017-1329-1

Effect of water on the fluorine and chlorine partitioning behavior between olivine and silicate melt

Contrib Mineral Petrol. 2017;172(4):15. doi: 10.1007/s00410-017-1329-1. Epub 2017 Mar 16.

Authors

Bastian Joachim^{1

2}, André Stechern³, Thomas Ludwig⁴, Jürgen Konzett¹, Alison Pawley⁵, Lorraine Ruzié-Hamilton⁵, Patricia L Clay⁵, Ray Burgess⁵, Christopher J Ballentine²

Affiliations

¹ Institute for Mineralogy and Petrography, University of Innsbruck, Innrain 52, 6020 Innsbruck, Austria.
² Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3 AN United Kingdom.
³ Institute for Mineralogy, Leibniz University of Hannover, Callinstrasse 3, 30167 Hannover, Germany.
⁴ Institute of Earth Sciences, Heidelberg University, In Neuenheimer Feld 234-236, 69120 Heidelberg, Germany.
⁵ School of Earth and Environmental Sciences, The University of Manchester, Manchester, M13 9PL United Kingdom.

Abstract

Halogens show a range from moderate (F) to highly (Cl, Br, I) volatile and incompatible behavior, which makes them excellent tracers for volatile transport processes in the Earth's mantle. Experimentally determined fluorine and chlorine partitioning data between mantle minerals and silicate melt enable us to estimate Mid Ocean Ridge Basalt (MORB) and Ocean Island Basalt (OIB) source region concentrations for these elements. This study investigates the effect of varying small amounts of water on the fluorine and chlorine partitioning behavior at 1280 °C and 0.3 GPa between olivine and silicate melt in the Fe-free CMAS+F-Cl-Br-I-H₂O model system. Results show that, within the uncertainty of the analyses, water has no effect on the chlorine partitioning behavior for bulk water contents ranging from 0.03 (2) wt% H₂O (D_Cl^ol/melt = 1.6 ± 0.9 × 10^-4) to 0.33 (6) wt% H₂O (D_Cl^ol/melt = 2.2 ± 1.1 × 10^-4). Consequently, with the effect of pressure being negligible in the uppermost mantle (Joachim et al. Chem Geol 416:65-78, 2015), temperature is the only parameter that needs to be considered for the determination of chlorine partition coefficients between olivine and melt at least in the simplified iron-free CMAS+F-Cl-Br-I-H₂O system. In contrast, the fluorine partition coefficient increases linearly in this range and may be described at 1280 °C and 0.3 GPa with (R² = 0.99): [Formula: see text]. The observed fluorine partitioning behavior supports the theory suggested by Crépisson et al. (Earth Planet Sci Lett 390:287-295, 2014) that fluorine and water are incorporated as clumped OH/F defects in the olivine structure. Results of this study further suggest that fluorine concentration estimates in OIB source regions are at least 10% lower than previously expected (Joachim et al. Chem Geol 416:65-78, 2015), implying that consideration of the effect of water on the fluorine partitioning behavior between Earth's mantle minerals and silicate melt is vital for a correct estimation of fluorine abundances in OIB source regions. Estimates for MORB source fluorine concentrations as well as chlorine abundances in both mantle source regions are within uncertainty not affected by the presence of water.

Keywords: Chlorine; Earth’s mantle; Fluorine; Forsterite; H2O; Halogen; Mid Ocean Ridge Basalt (MORB); Ocean Island Basalt (OIB); Olivine; Partitioning; SIMS; Water.