Variscan events in the Alpine region

Abstract

Relics of the pre-Permian history are preserved in the five crystalline basement complexes of the External or Helvetic realm. Their evolution can be compared with the Variscan regional evolution in Central Europe. Precambrian to Palaeozoic sediments interlayered with acid and basic magmatic rocks suffered an early regional anatexis with contemporaneous formation of granitoid rocks. This event (5-6 kb/700 °C) supposed to be at least of Caledonian age is followed by the formation of blastomylonite zones probably contemporaneous to large scale B 3-folds. A second regionaI anatexis (of probably early Variscan age, 650-700 °C/4 kb) is characterized by the regional occurrence of cordierite-bearing granitoids, accompanied or followed by a regional growth of biotite and plagioclase. The later history is dominated by the intrusion of distinct granite bodies. Although Variscan events are of importance for the structural evolution, the main metamorphic history is of pre-Variscan age. No considerable break could be seen in the rather continuous history of evolution from Caledonian until Variscan time.