Natural and experimental fluorine substitution in biotite: Implications for fluid-rock thermochronometry and application to the Seridó Belt, northeastern Brazil

Chemical diffusion of fluorine in phlogopite

“…As such, the diffusion of fluorine in the phlogopite samples was probably dominated by the binary interdiffusion of fluorine and hydroxyl. This has been proposed as the main mechanism for the chemical diffusion of fluorine in biotite (Sallet et al, 2018) and the ionic exchange of fluorine between fluorine-bearing silicate minerals (e.g., apatite and tremolite) and hydrothermal fluids (Brenan, 1994;Brabander et al, 1995). Similar mechanism by the exchange with hydroxyl has also been proposed…”

“…Concerning fluorine diffusion, the only available data for minerals are those on the chemical diffusion in titanite, a very preliminary result reported in a conference abstract (Berds et al, 2008), and biotite (Sallet et al, 2018). The former experiments were done at dry conditions by exchange with a fluorine-rich apatite, and the latter at hydrothermal conditions by fluorine exchange between tiny biotite grains and a hydrous hydrofluoric (HF) acid, with some grains in the run products analyzed for the fluorine profiles along the interlayers.…”

“…In either case, our diffusivity data can be reasonably applied, and the GM data are meaningful for the modeling. The cooling rate of phlogopite-bearing samples (e.g., xenoliths) or complex has not been well established, but is usually larger than 1 ºC/Myr (Hammouda and Cherniak, 2000;Sallet et al, 2018). The closure temperature obtained at 1 ºC/Myr (Fig.…”

“…GPa (Fortier and Giletti, 1991), and Sr (H00, //c) is Sr chemical diffusion (//c) at 1 bar (Hammouda and Cherniak, 2000); and (b) biotite (S18, ⊥c) is F chemical diffusion ⊥c at 0.4 GPa (Sallet et al, 2018) and titanite (B08) is F chemical diffusion at 0.5-1 bars (Berds et al, 2008). Direction //c in available reports corresponds to ⊥(001) in this study.…”

Fluorine behavior during experimental muscovite dehydration melting and natural partitioning between micas: Implications for the petrogenesis of peraluminous leucogranites and pegmatites

“…(iii) fluid-absent biotite and amphibole dehydration melting at higher temperatures, in the range of 850 to 900 °C (e.g., Michaud et al 2021;Patiño Douce and Beard 1995;Peterson et al 1991;Pickering and Johnston 1998;Sallet et al 2015;Skjerlie and Johnston 1993;Thompson 1982;Vielzeuf and Holloway 1988) Fluid-absent melting reactions by dehydration of micas (and amphibole) implies a potential fractionated OH-F-Cl release from their hydroxyl site to the melt. Consequently, the residual and neo-formed hydroxyl bearing phases may acquire different OH-F-Cl compositions (e.g., Fink and Thompkins 2017;Hansen and Harlov 2007;Peterson et al 1991;Pickering and Johnston 1998;Sallet et al 2015Sallet et al , 2018. On the other hand, anatexis under fluid saturation by external influx at near eutectic temperatures may allow the micas to remain stable while quartz + feldspars experience partial melting (Weinberg and Hasalovà 2015, and references therein).…”