Local variations of metamorphic record from compositionally heterogeneous rocks (Cima di Gagnone, Central Alps): Inferences on exhumation processes of (U)HP–HT rocks

摘要: Abstract The record of metamorphic conditions is commonly highly heterogeneous in spatially close rocks different composition and rheology. well-studied Cima di Gagnone area the Central Alps represents such an example, as relatively small, 1– to 100 s-meter scale, ultrahigh–pressure high–temperature ultramafic lenses are enveloped within amphibolite–facies metasediments. We present new field observations, microstructural petrological analyses, thermodynamic modelling results on these metasediments, showing that generally experienced medium pressure temperature 1.0–1.2 GPa 640–700 °C, followed by a retrograde stage around 0.6–0.8 GPa 600–675 °C. However, few samples from immediate proximity significantly higher P–T 1.3–1.7 GPa 750–850 °C, approaching high bodies (1.5–3.1 GPa, 650–850 °C). Mineral/bulk chemistry changes during growth mineral phases hint local melt/fluid interaction (i.e., metasomatism) between metasediments ultramafics deformation. Preliminary U Pb LA–ICP–MS dating suggests zircon grains metasomatic reaction zone have been fully re–equilibrated early Alpine exhumation (~36 Ma), while large part records only pre–Alpine ages. finally recast data into regional P–T–t–D paths discuss consequences findings for understanding processes HP rocks. found equilibria (ΔP up 2 GPa; ΔT 160 °C) cannot be explained simply metamorphism or tectonic amalgamation. Rather, our work significant role deformation producing variable