Major fault zones in the Austroalpine units of the Kreuzeck Mountains south of the Tauern Window (Eastern Alps, Austria)

Abstract

The Kreuzeck Mountains are located between the Tauern Window in the north and the Southalpine unit in the south. They expose an Eoalpine (Cretaceous) nappe stack of Adria derived continental crust. The Koralpe–Wölz Nappe System in the footwall partly experienced Cretaceous eclogite-facies metamorphism, while the Drauzug-Gurktal Nappe System in the hanging wall remained at anchizonal to greenschist-facies conditions in Cretaceous time. From the Late Cretaceous onward the Austroalpine units in the Kreuzeck Mountains were affected by brittle/ductile shearing and brittle deformation. This contribution is based on mapping of the southeastern part of the Kreuzeck Mountains at the 1:10000 scale in combination with structural and petrological investigations and Rb–Sr biotite dating. The new data indicate that the boundary between the Koralpe–Wölz Nappe System and the overlying Drauzug-Gurktal Nappe System consists of three segments. It includes (1) the south dipping Wallner Normal Fault representing a more than 500 m wide shear zone responsible for the Cretaceous exhumation of the eclogite-bearing Polinik Complex to shallow crustal levels (2) the Oligocene to Miocene Ragga-Teuchl Fault and (3) the Großhalsgraben Fault. The latter is mechanically related to the Mölltal Fault and shows a dextral offset. The Drauzug-Gurktal Nappe System is from bottom to top composed of the Strieden, the Gaugen and the Goldeck complexes, which are transgressively overlain Permo-Triassic (meta)sediments. It is dissected by the steeply north dipping Lessnigbach Shear Zone with a dominant top to the south reverse sense of shear and the ENE–WSW trending, sub-vertical Blassnig Shear Zone showing sinistral kinematics. Both faults were active in the Late Cretaceous, but might have been initiated in the Late Jurassic.