Growth of kyanite and Fe‐Mg chloritoid in Fe₂O₃‐rich HP–LT metapelites and metapsammites: A case study from the Massa Unit (Alpi Apuane, Italy)

Chloritoid and kyanite coexist in metapelites from the high-pressure/low-temperature Massa Unit Alpi Apuane metamorphic complex (Northern Apennines, Italy). The composition of chloritoid is extremely variable throughout Unit. Fe-chloritoid occurs association with hematite-free, graphite-bearing schists, whereas strongly zoned Fe-Mg found hematite kyanite. We investigated effect different bulk Fe2O3 contents controlling through phase equilibria modelling four selected samples, representative chloritoid-bearing parageneses ferric iron content, measured wet chemical titration, ranges 0 (graphite-chloritoid schist) to 73% total (hematite-chloritoid schist). show that Mg-rich compositions stability at greenschist- blueschist-facies conditions can be reproduced MnO–Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O–TiO2–O (MnNKFMASHTO) system only considering presence significant amounts as part composition. stabilization lower grade directly linked Fe2O3, which renders reactive rock effectively enriched Al2O3 respect Fe Mg. also document high exacerbate fractionation, producing Fe-Mg-chloritoid grains. Finally, P-T Units performed this study allows, for first time, recognition a two-stage evolution peak conditions, an earlier pressure (1.2 – 1.3 GPa 350 400 °C), later thermal (0.7 1.1 440 480 compatible subduction, underthrusting exhumation Adria continental margin during growth northern Apennine orogenic wedge.