The Klagenfurt Basin in the Eastern Alps: An intra-orogenic decoupled flexural basin?

The Klagenfurt Basin is an E-W-trending narrow Sarmatian to Quaternary flexural basin formed by flexure of the Austro-Alpine lithosphere by loading through the southerly adjacent Karawanken Mountains in the Eastern Alps (Austria). The tectonic evolution of the basin is kinematically connected to Miocene brittle transpressive dextral strike-slip deformation along the Periadriatic Fault which separates the South Alpine unit from the Austro-Alpine unit in the Eastern Alps. The final NW-directed overthrust of the Karawanken Mountains onto the foreland is characterised by a positive flower structure, which is kinematically linked to dextral transpressive shearing along the Periadriatic Fault. Only a small part of the lithosphere appears to support the regional isostatic response to the load by the Karawanken Mountains. The area is characterised by a crustal thickness between 40 and 45 km, elevated heat flow and a strength distribution which suggests that only the upper crust elastically supports the topographic load. Ductile flow of the lower crust is also supported by the absence of a crustal root beneath the Karawanken chain. Rheologic models for this lithospheric configuration indicate a mechanical decoupling of upper crust, lower crust and mantle and generally low strengths for the lower crust and mantle.