Peak Alpine metamorphic conditions from staurolite‐bearing metapelites in the Monte Rosa nappe (Central European Alps) and geodynamic implications

The tectono-metamorphic evolution of the European Alps is still contentious. Monte Rosa tectonic unit a prominent nappe in Central and estimates its peak Alpine pressure (P) temperature (T) conditions are essential for reconstructing evolution. However, reported vary considerably between 1.2 2.7 GPa 490 640°C variety lithologies. Here, we show petrology pseudosection modelling metapelitic assemblages from western portions (upper Ayas valley, Italy). We present newly discovered staurolite–chloritoid-bearing assemblages. These exhibit an high-P metamorphic overprint former contact-metamorphic mineral assemblage generated by post-Variscan granitic intrusions. Staurolite contains major amounts Zn (up to 1.0 atoms per formula units), which currently, contrast Fe- Mg-staurolite end-members, not considered any thermodynamic database. employ two end-member mixing models staurolite, site mixing, molecular mixing. Both enlarge stability range observed assemblage, where has largest influence ±0.2 ±20°C. Our results three metapelite assemblages, with without indicate 1.6 ± 0.2 585 20°C. agree previously published metagranites nappe, stark obtained talc-, chloritoid-, phengite-, quartz-bearing lithologies termed ‘whiteschists’ (>2.2 GPa). confirm variation 0.6 metagranite/metapelite nearby whiteschist lens GPa) within metagranite. Field observations that studied region structurally coherent slice formed mélange. suggest consistent metagranite represents regional higher recorded likely due dynamic pressure, possibly resulting and/or reaction-induced stresses. If calculated conditions, then was exhumed significantly shallower depth than assumed, based on > 2.2