Metamorphic structure and P-T conditions of the metapelitic constituent of the ZEV

Bounded by mylonite zones and imbrications the Zone of Erbendorf-Vohenstrauss is built up by medium- and low-pressure amphibolite-facies metapelites associated with amphibolites and biotite-hornblende gneisses, and intruded by the Leuchtenberg granite. Pelitic index assemblages define the staurolite-kyanite-, the garnet-kyanite-, the garnet-sillimanite-and the garnet-kyanite-sillimanite zone of medium pressure metamorphism, which is estimated at P = 5-9.6 kbar and T = 580-730 degrees C, and the cordierite zone of subsequent low-pressure metamorphism, which is estimated at P < 4.5 kbar and T less than or equal to 700 degrees C. Both facies series probably are tectonically juxtaposed. Staurolite-kyanite- and garnet zones are related by the reaction: staurolite + muscovite + quartz = garnet + aluminium-silicate + biotite + H2O. This relation defines the only observable trace of a field gradient in the ZEV. An early sillimanite generation (sillimanite I) is found in all mineral zones as mineral inclusions in garnet rims. Post-P-T-max evolution is indicated by the inversion kyanite double right arrow sillimanite (sillimanite II), the reaction: garnet + muscovite double right arrow sillimanite (sillimanite III) + biotite + quartz and by X-Fe decreasing in garnet rims. Garnet is resorbed under the conditions of stable kyanite + sillimanite + muscovite + quartz. Some staurolite-kyanite zone garnets show two stages separated by resorption which may be ascribed to published Ordovician and Late Devonian radiometric ages. The second garnet generation formed near 9.7 kbar/ 620-660 degrees C. No evidence for high-pressure metamorphism was found. Comparison of the medium-pressure part of the ZEV with the Zone of Tepla-Domazlice (Czech Republic) and with garnet-kyanite rocks at the northern edge of the Black Forest seems possible. The low-pressure cordierite rocks are similar to metapelites framing the Winklarn eclogites towards southeast of the ZEV, but are in contrast to the Moldanubian-type cordierite gneisses.