The Friningen Garnet Peridotite (central Sweden): a good example of the characteristic PTt path of a cold mantle wedge garnet peridotite

Abstract

were traditionally interpreted as fragments of sub-oceanic, Iapetus-related, lithosphere, incorporated into the Scandian nappe pile during the Caledonian orogeny. This interpretation was first challenged by Van Roermund (1989) who described for the first time the occurrence of garnet-bearing peridotites from an area around lake Friningen, northern Jämtland, central Sweden. Here the ultramafic bodies consist dominantly of garnet-dunite, -harzburgite and - lherzolite, with minor internal eclogite- and/or garnet pyroxenite layers/dikes. In one of these bodies, called the Friningen Garnet Peridotite (FGP), evidence was found of an Archean to mid Proterozoic origin for the M1 mineral assemblage as well as an early Caledonian (≈ 454 Ma) age for a second (M2) HP mineral assemblage (Brueckner et al., 2004). More recently, evidence for UHPM conditions was found in the M2 mineral assemblage of the internal eclogite/garnet pyroxenite dike (Janàk et al., 2012). However, in all studies reported above the characteristic Pre-Caledonian metamorphic conditions of the FGP were not determined adequately. This concerns the topic of the present work.