Permian high-temperature metamorphism in the Western Alps (NW Italy)

Barbara Kunz, P. Manzotti, Brigitte von Niederhaeusern, Martin Engi, James Darling, Francesco Giuntoli, Piere Lanzari

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    During the late Palaeozoic, lithospheric thinning in part of the Alpine realm caused high-temperature low to medium pressure metamorphism and partial melting in the lower crust. Permian metamorphism and magmatism has been extensively recorded and dated in the Central, Eastern and Southern Alps. However, Permian metamorphic ages in the Western Alps so far are constrained by very few and sparsely distributed data. The present study fills this gap. We present U/Pb-ages of metamorphic zircon from several Adria-derived continental units now situated in the Western Alps, defining a range between 286 and 266 Ma. Trace element thermometry yields temperatures of 580–890°C from Ti-in-zircon and 630–850°C from Zr-in-rutile for Permian metamorphic rims. These temperature estimates, together with preserved mineral assemblages (garnet–prismatic sillimanite–biotite–plagioclase–quartz–K-feldspar–rutile), define pervasive upper-amphibolite to granulite facies conditions for Permian metamorphism. U/Pb-ages from this study are similar to Permian ages reported for the Ivrea Zone in the Southern Alps and Austroalpine units in the Central and Eastern Alps. Regional comparison across the former Adriatic and European margin reveals a complex pattern of ages reported from late Palaeozoic magmatic and metamorphic rocks (and relics thereof): two late Variscan age groups (~330 Ma and ~300 Ma) are followed seamlessly by a broad range of Permian ages (300–250 Ma). The former are associated with late-orogenic collapse; in samples from this study these are weakly represented. Clearly dominant is the Permian group, which is related to crustal thinning, hinting to a possible initiation of continental rifting along a passive margin.
    Original languageEnglish
    Number of pages28
    JournalInternational Journal of Earth Sciences
    Early online date24 May 2017
    Publication statusEarly online - 24 May 2017


    • Permian HT metamorphism
    • Western Alps
    • Adriactic margin
    • zircon geochronology


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