Fluorine partitioning between eclogitic garnet, clinopyroxene, and melt at upper mantle conditions

Abstract

partition coefficients between olivine and melt at least in the simplified iron-free CMAS+F-Cl-Br-I-H 2 O system. In contrast, the fluorine partition coefficient increases linearly in this range and may be described at 1280 °C and 0.3 GPa with (R 2 = 0.99):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 Fluorine · Chlorine · Halogen · Partitioning · Water · H2O · Earth's mantle · Mid Ocean Ridge Basalt (MORB) · Ocean Island Basalt (OIB) · Olivine · Forsterite · SIMS 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-H 2 O 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% H 2 O (D Cl ol/melt = 1.6 ± 0.9 × 10 −4 ) to 0.33 (6) wt% H 2 O (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 Communicated by

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

“…Experiments of that study were, however, not only performed with varying melt water contents but also at different temperatures, which may strongly affect the partitioning behavior (Joachim et al 2015 ). Results of other studies seem to indicate that there is no effect of water on the fluorine partitioning behavior between orthopyroxene and melt (Hauri et al 2006 ), clinopyroxene and melt (O’Leary et al 2010 ; Beyer et al 2016 ), or garnet and melt (Hauri et al 2006 ; Beyer et al 2016 ) at Earth’s mantle conditions. Our study also does not consider a potential effect of iron (and f O 2 ) on the partitioning behavior.…”

“…In a recent study, Beyer et al ( 2016 ) discuss a potential process to generate magmas with a high F/H 2 O ratio in the upper mantle. In their model, bulk fluorine and water partition coefficients between mantle minerals and melt are kept constant regardless of potential effects of pressure, temperature, or bulk water content.…”

“…This will decrease the solidus temperature and may lead to small degree partial melting. The model of Beyer et al ( 2016 ) shows that the F/H 2 O ratio in the residual increases with increasing melt percentage, which is dependent on the amount of water that is added to the system. Simultaneously, addition of small amounts of water will increase the fluorine partition coefficient between olivine and melt (Fig.…”

“…By combining experimentally determined partition coefficients with natural halogen concentrations in oceanic basalts, halogen source region concentrations can be estimated. Recent experimental studies determined fluorine and chlorine partitioning data at pressure and temperature (P–T) conditions relevant for MORB and OIB source mantle regions between olivine, pyroxene, and corresponding silicate melt (Hauri et al 2006 ; O’Leary et al 2010 ; Beyer et al 2012 , 2016 ; Dalou et al 2012 ; Joachim et al 2015 ; Rosenthal et al 2015 ). Joachim et al ( 2015 ) showed that fluorine partitioning into olivine increases at nominally dry conditions by about two orders of magnitude between 1350 and 1600 °C at pressures ranging from 1 to 2.3 GPa.…”

Halogens (F, Cl, Br, I) in Thirteen USGS, GSJ and NIST International Rock and Glass Reference Materials

“…The SHRIMP technique utilised in both SHRIMP-II and SHRIMP-SI sessions was similar to that of Beyer et al (2016). The sample mount was held in the SHRIMP ultrahigh-vacuum sample chamber at a potential of -10 kV and targeted with a primary Cs + ion beam focused to ã 30 lm spot on the sample.…”