THE BOLLSTEIN ODENWALD - EVIDENCE FOR PRE-VARISCAN TO EARLY VARISCAN PLATE CONVERGENCE IN THE CENTRAL-EUROPEAN VARISCIDES

New chemical, petrological and structural data characterize the pre- to Early Variscan evolution of the Eastern or Bollstein Odenwald, which forms a part of the Mid-German Crystalline Rise. This part of the Odenwald Crystalline Complex is different to the Western or Bergstrasser Odenwald with respect to the age of the magmatic events, the structures, chemistry and metamorphism. The complex is formed by a large anticline composed of an older metamorphosed volcano-sedimentary unit and a younger metagranitoid core. The volcano-sedimentary sequence represents a relic of a pre-Variscan accretionary prism with relics of older island-arc volcanics, formed in front of a continental margin. During the Silurian to Lower Devonian the prism was intruded by S-type granitoids. The acidic intrusions were followed by a series of basic intrusives with an island-arc signature. After the magmatic phases the complex was metamorphosed under probably pre-Variscan medium pressure and high temperature conditions. During Variscan times the rocks underwent multiple penetrative deformations under pressure - temperature conditions or partial melting. The main deformation produced isoclinal folds and had a sense of movement of top to the west. During subsequent deformation the anticlinal structure and the Otzberg fault zone were formed and later overprinted by two generations of open folds with vertical and horizontal axes. The rocks of the Bollstein Odenwald document multiple plate convergences of pre- to Early Variscan to Upper Visean age.