Coeval high-pressure metamorphism, thrusting, strike-slip, and extensional shearing in the Tauern Window, Eastern Alps

Abstract

Recent findings for a young (31.5 ± 0.7 Ma) age of high-pressure metamorphism at ∼90 km depths in the Eclogite Zone of the Tauern Window, Eastern Alps, prompt the question about the timing of the structural development of the Tauern Window and its relation to high-pressure metamorphism. We show that all major structures in the Tauern Window, resulting from strong N-S lithospheric shortening and simultaneous minor E-W extension, began developing coevally with high-pressure metamorphism in the Eclogite Zone. Large-scale strike-slip shear zones started to form at ∼32-30 Ma and facilitated the spatial accommodation of simultaneous shortening and extension. At least some of the strike-slip and extensional shear zones operated into the Middle Miocene, either continuously or intermittently, with pronounced activity at ∼21-15 Ma. The considerable exhumation of the Eclogite Zone from ∼90 km depths into the middle crust, and the tectonic development of its framework occurred within only 1-2 Ma after eclogitization. This is evidenced by almost identical ages for eclogite facies metamorphism and for the development of the major structures that bound the Eclogite Zone under blueschist- and greenschist facies metamorphic conditions. We discuss a tectonic model in which considerable transpressional shortening and thickening took place in the present central-southern part of the Tauern Window. We propose that the Tauern Window nucleated here and that most of the regional deformation at ∼32-30 Ma is today found at the periphery of the window and in the adjacent Austroalpine units. Afterward, transpression continued, the window grew to the E, W, and N, and deformation progressed to those parts of the window. Ductile deformation in the present-day surface level ceased at ∼15 Ma. Copyright 2008 by the American Geophysical Union.