Effect of chlorine on water incorporation in magmatic amphibole: experimental constraints with a micro-Raman spectroscopy approach

Abstract. Amphibole represents an important repository of water (among other volatiles, e.g., chlorine and fluorine) in the lithosphere all those environments characterized by circulation fluids hydrous melts, such as subduction zones subcontinental lithospheric mantle. Therefore, detailed knowledge mechanisms ruling incorporation amphibole is essential to assess amount that can be fixed this mineral and, ultimately, gain a better insight into deep cycle. Water incorporated structure hydroxyl (OH?), which hosted anion site O(3), mainly controlled oxo-substitution mechanism M(1)Ti14++O(3)O22- M(1)(Mg2+, Fe2+)-1+ O(3)(OH-)-2-. However, melts circulating mantle variably enriched halogens (Cl? F?) substitute OH? O(3) amphibole, thus potentially affecting its budget. The aim study evaluate effect Cl on amphibole. End-loaded piston cylinder experiments were conducted at pressure temperature conditions compatible with upper-mantle depth (1.4 GPa 1015–1050 ?C) order favor crystallization equilibrium coexisting melt. Alkali basalt powder was used starting material, doped different contents added each experiment. Two ranges oxygen fugacity (fO2) investigated ?FMQ = ?2.6 (log fO2 [experiment] ? log [FMQ buffer]) +1.7, where FMQ fayalite–magnetite–quartz, preliminarily identify potential influence budget In contribution, we propose new method quantify amphiboles using confocal micro-Raman spectroscopy. H2O range from 2.20 ± 0.10 wt % 5.03 0.47 glasses 0.93 0.08 1.50 0.12 amphiboles, resulting partition coefficient between glass (Amph/LDH2O) ranging 0.29 0.06 0.52 0.08. Our results show positive correlation content (from 0.18 0.88 %) Amph/LDH2O. This ascribed influences impeding entrance Ti4+ M(1) sites preventing dehydrogenation. reported study, related change crystal structure, highlights high concentrations magmatic systems rather than melt, although exchange Amph/LDH2O Amph/LDCl supports preferential over presence abundant hydration state magmas evolving towards crustal roots