Is the transition zone a deep reservoir for fluorine?

Abstract

International audienceIt is now recognized that the transition zone (TZ) is a significant repository for water. This means that other volatile species may also be stored in this region such as halogen elements. We have measured the solubility of fluorine in wadsleyite (Wd) and ringwoodite (Rw) under hydrous and anhydrous conditions at different pressures and temperatures, relevant for the transition zone. F contents are similar in Wd (665 to 1045 ppm F, up to 956 ppm H2O) and in Rw (186 to 1235 ppm F, up to 1404 ppm H2O). This suggests that F may be incorporated in the same manner as water in the major nominally anhydrous minerals of the TZ: ringwoodite and wadsleyite and that the transition zone could be a major reservoir for fluorine. In the framework of the “water filter model” proposed by Bercovici and Karato (2003), the contrast of volatile element contents between a depleted upper mantle and an enriched transition zone could be maintained over geological time scales. Previous estimates of the fluorine content of the Bulk Silicate Earth (BSE), such as 25 ppm by mass (McDonough and Sun, 1995), have assumed a homogeneous mantle. Although we do not know whether the TZ is F saturated or not, we used our new experimental data and estimates of the lower mantle F content from ocean island basalts to estimate a maximum BSE fluorine content of 59 ppm by mass for a hydrous, F-saturated TZ. This upper bound on the range of possible BSE F content emphasizes the challenges when explaining the origin of volatile elements in the Earth from a carbonaceous chondrite late veneer

Operando analysis of lithium profiles in Li-ion batteries using nuclear microanalysis

“…We presented operando RBS and PIGE measurements applied to measure the lithium and the In summary, we have demonstrated how powerful ion beam techniques can be for investigating the lithium profile in lithium batteries. Interestingly, the distribution of others elements such as sodium or magnesium is also possible using the reaction 23 Na(p,p') 23 Na at 439 keV or 24 Mg(p,p') 24 Mg at 1368 keV [21,22] and is believed to be of great interest for studying reaction and degradation mechanisms in Na-ion and Mg-ion batteries.…”

GGR Biennial Critical Review: Analytical Developments Since 2014

“…In Roberge et al . (), coupled micro‐IBA methods (PIXE, PIGE, RBS, ERDA) were used to measure F and H in wadsleyite and ringwoodite under hydrous and anhydrous conditions relevant for the transition zone. Crystals of olivine, wadsleyite and ringwoodite could be clearly identified in the synthesised samples, and chemical heterogeneities such as NaF‐rich fine intergrowths in the grain boundaries could be detected.…”

“…Cr episson et al (2014) investigated fluorine incorporation in H-bearing forsterite, with high F solubilities (1715 and 1308 lg g -1 ) measured by PIGE in samples synthesised at 2 and 4 GPa, respectively, while ERDA was used to quantify H. The existence of clumped fluoride-hydroxyl defects in these nominally anhydrous minerals suggested that the F geodynamical and water cycles are strongly coupled. In Roberge et al (2015), coupled micro-IBA methods (PIXE, PIGE, RBS, ERDA) were used to measure F and H in wadsleyite and ringwoodite under hydrous and anhydrous conditions relevant for the transition zone. Crystals of olivine, wadsleyite and ringwoodite could be clearly identified in the synthesised samples, and chemical heterogeneities such as NaF-rich fine intergrowths in the grain boundaries could be detected.…”

Electrical Conductivity of Fluorite and Fluorine Conduction

“…Therefore, the potential of fluorine as an important charged species in the electrical conduction of Earth materials (in particular silicate minerals) must be considered. This is because: (1) fluorine may be stored in appreciable amounts of a few hundred to several thousand ppm in many minerals in the deep mantle such as olivine, garnet, pyroxenes, wadsleyite and ringwoodite [36][37][38], (2) fluorine-abundant phases such as phlogopite could be regionally enriched in the deep crust and upper mantle, leading to very high electrical conductivity in regional areas [17,20], and (3) the sensitivity of conductivity to fluorine may be comparable to H in nominally anhydrous minerals [17], and at higher temperature, the effect of fluorine on enhancing the conductivity of the host minerals exceeds that of H (protons) and thus dominates bulk conductivity, due to the much larger activation enthalpy of fluorine conduction (e.g., 130-220 kJ/mol) relative to proton conduction,~70-90 kJ/mol [2][3][4][5][6][7][8][9][10][11][12][13] (Figure 5). This would shed fundamental insight into the electrical structure of the deep Earth, although further experimental studies on other minerals are necessary.…”