A diachronous record of metamorphism in metapelites of the Western Gneiss Region, Norway

In this study, data from garnet-kyanite metapelites in ultrahigh-pressure (UHP) domains of the Western Gneiss Region (WGR), Norway, are presented. U–Pb geochronology and trace element compositions zircon, monazite, apatite, rutile garnet were acquired, pressure–temperature (P–T) conditions calculated using mineral equilibria forward modelling Zr-in-rutile thermometry. Garnet-kyanite gneiss Ulsteinvik record a prograde evolution passing through ~690–710°C ~9–11 kbar. Zircon age thermometry indicate these significantly pre-date Silurian UHP subduction WGR interpreted to early Caledonian continental-derived allochthons. Minimum peak metapelite occur at ~28 kbar, constrained by an inferred garnet+kyanite+omphacite+muscovite+rutile+coesite+H2O assemblage. The retrograde passed ~740°C ~7 first recorded destruction omphacite followed partial replacement kyanite cordierite spinel. diamond-bearing Fjørtoft outcrop documents polymetamorphic history, with forming during late Mesoproterozoic limited preservation high-pressure assemblages. Similar metapelite, zircon also pre-Scandian ages. Two potential tectonic scenarios possible: (1) samples exhumed different times Blåhø nappe, or (2) do not share history same nappe complex, instead is constituent Seve-Blåhø Nappe, whilst shares its within separate complex.