High T/P metamorphism at 1.45 Ga: P-T evolution and SIMS U-Pb zircon ages of paragneisses from southernmost Sweden

Petrography, bulk and mineral geochemistry and pseudosection modelling show that the rocks underwent prograde staurolite-sillimanite grade metamorphism peaking at upper amphibolite to granulite conditions, with the formation of Crd + Sill + Grt + K-fsp + Ilm + Melt Spl Bt. The rocks followed a clockwise P-T path with heating during decompression and partial melting. Later stages involved the formation of sillimanite + biotite at the expense of garnet and cordierite. Local low-temperature and fluid-assisted retrogression caused the formation of chlorite and muscovite at the expense of cordierite and garnet, and pseudomorphism of ilmenite by rutile-rich fine-grained intergrowths. Both granites and paragneisses contain complex zircon grains with inherited 1.7 Ga igneous cores and high-U, low-Th secondary zircon, mainly reworked rims c. 1.45 Ga old. The P-T evolution demonstrates burial and exhumation in a high T/P environment, with coeval granitic magmatism. These conditions are in accordance with an accretionary orogenic setting.