Eclogite-facies rocks in the Saxonian Erzgebirge,Germany: high pressure metamorphism under contrasting P-T conditions

The metamorphic sequences of the Saxonian Erzgebirge were thoroughly overprinted by a Variscan medium-pressure event under amphibolite facies conditions. However, eclogitic relics documenting an older high-pressure event are widespread. P-T conditions of the eclogite-facies metamorphism systematically decrease, over a distance of 50 km, from about >29 kbar/850°C, in the central part, to 20–24 kbar/650°C, in the westernmost part of the Erzgebirge crystalline complex. A distinct gap in P-T conditions exists between the central and the western Erzgebirge coinciding with the fault zone of the Flöha syncline. Therefore, the eclogitebearing sequences are assumed to represent at least two different nappe units. The lower-grade eclogite assemblages in the western Erzgebirge display a continuous metamorphic zonation with a gradual decrease of peak metamorphic temperatures towards the west. Assemblages formed in the stability field of coesite and thus indicating a regional ultra-high pressure metamorphism, are restricted to the central Erzgebirge, where they are widespread in the eclogites, but also present in metaacidic country rocks. The same high-temperature/high-pressure conditions, testifying to a burial of at least 100 km, were independently recorded for the ultramafic garnet pyroxenites associated with the eclogites of the central Erzgebirge. Mineral relics included in the eclogite phases and mineral assemblages formed by retrograde reactions permit reconstruction of the prograde and retrograde P-T paths in the different parts of the Erzgebirge crystalline complex.