MAGMATIC AND METAMORPHIC EVOLUTION OF METAGABBROS IN THE MUNCHBERG MASSIF, NE BAVARIA

The central gneiss complex of the Munchberg Massif consists of the Liegendserie at the base and the Hangendserie at the top. Metagabbros are found in the Liegendserie; eclogites occur in the Hangendserie. New isotope data revive the discussion whether a genetic relationship exists between metagabbros and eclogites in the Munchberg Massif. It is possible to relate the two types of rocks to the same protoliths by variable degrees of crustal contamination and magmatic accumulation. Therefore, a common magmatic origin may be assumed. Both the metagabbros and the eclogites were affected by amphibolite-facies metamorphism. The amphibolitization of the metagabbros was a prograde metamorphic event. Increasing temperature is indicated by inverse zonation of recrystallized plagioclase and increasing Mg/Fe ratios in garnet from core to rim. Geothermobarometry yields a temperature of 600-degrees-C and a pressure of about 11 kbar for the peak of metamorphism. In contrast, the eclogites underwent a first high-pressure stage at a minimum pressure of 14 kbar and a temperature estimated at 600-degrees-C and were subsequently overprinted under amphibolite-facies conditions at 10 kbar/700-degrees-C. A common magmatic origin of metagabbros (Liegendserie) and eclogites (Hangendserie) of the Munchberg Massif can no longer be discarded. However, the converging P -- T -- t paths reflect a different geodynamic evolution of the Liegendserie and the Hangendserie after magmatism and before amphibolite-facies metamorphism.