Dissolution and Reprecipitation of Garnet during Eclogite-facies Metamorphism; Major and Trace Element Transfer during Atoll Garnet Formation

Abstract Garnet commonly accommodates high contents of Mn + Y heavy rare earth elements (HREE) that follow Rayleigh fractionation during garnet early growth, with the exception overstepping nucleation (late crystallization owing to reaction overstepping). Because this, as porphyroblasts form mostly in equilibrium surrounding matrix, concentration these continuously decreases towards porphyroblast rims. Yet rapid changes progress a rock namely resorption–dissolution minerals concentrations REE, may create an anomaly or peak mantle rim grains. In this study we present example resorption cores and formation atoll textures eclogite from Krušné hory (in Saxothuringian tectonic zone Bohemian Massif). Based on textural relations, show grains studied rocks were formed prograde stage blueschist- eclogite-facies metamorphism. Preliminary observations showed full (non-atoll) had compositionally different (interior, I) rims (ring, II) separated by HREE medium REE (MREE) peak. The ring II indicated elevated comparison marginal parts interior I. Therefore, minor less vulnerable diffusion than major strongly sensitive broad spectrum geochemical processes, such used track possible mineral reactions whole growth path. Thermodynamic modelling breakdown chlorite lawsonite/zoisite, peak-pressure phases represented garnet, omphacite, quartz, amphibole, rutile, talc. To quantify sources MREE sharp peaks, sequences dissolution I leading structure investigated. addition thermodynamic pressure–temperature path constraints, mass-balance calculations trace also performed. results combined observed compositional relations indicate peaks at interface two types controlled complex mechanism included texture, stepwise increasing pressure temperature, decomposition elements, zoisite/epidote lawsonite.