Tectonometamorphic evolution of the Koralm Complex (Eastern Alps): constraints from microstructures and textures of the ‘Plattengneis’ shear zone

摘要: Abstract Lattice preferred orientations (LPO) of quartz have been investigated along a south–north oriented section across the Plattengneis Koralm Complex (Eastern Alps). The forms an important shear zone within Austroalpine nappe complex Eastern Alps, which has developed during Cretaceous evolution Alpine orogen. c -axes form small circle distributions in southernmost parts Complex, represent uppermost structural level Plattengneis. Further to North two maxima between Y and Z directions finite strain can be interpreted terms slip on rhomb planes. These fabrics continuously grade into (type I type II crossed) girdle northward direction. A strong maximum near -axis with tendency distributed single girdle, three corresponding margin pole figure, observed central northern parts. Such LPO are characteristic for both high metamorphic conditions strain. microstructures display that deformation was synmetamorphic. continuous increase peak temperatures (and pressure) from approximately 550 °C 750 °C South inferred geothermometric calculations. then decrease 650 °C North. related pressures 8 16 kbar, 10 kbar. changes study area best temperature dependence activation glide systems aggregates. pressure may indicate exhumed by larger amounts than southern This is also documented evolution. Therefore, we assume formed exhumation high-pressure units footwall this zone. Accordingly, kinematics rather extensional thrust-related. implications Alps shortly discussed.