Transition from orogen-perpendicular to orogen-parallel exhumation and cooling during crustal indentation - Key constraints from 147Sm/144Nd and 87Rb/87Sr geochronology (Tauern Window, Alps)

- We integrate new 87Rb/86Sr and 147Sm/144Nd ages to show how cooling migrated within the Tauern Window.
- The evolution of exhumation and cooling of European orogenic crust in the Tauern Window is discussed.
- We show that diachronous exhumation of the Tauern Window was related to the indenter fragmentation.
- We propose a model of indentation in which orogen-normal exhumation is transitional to orogen-parallel exhumation.

The core of the Alpine orogen in the Eastern Alps (Tauern Window) experienced a change from orogen-normal shortening and post-nappe doming to predominantly orogen-parallel extension and tectonic unroofing during late Oligocene to Miocene northward indentation of the Adriatic Microplate. A new 147Sm/144Nd isochron age of 25.7 ± 0.9 Ma on a garnet-bearing assemblage from the lowest nappe complex forming a dome in the eastern part of the Tauern Window indicates that high temperatures related to post-nappe Barrovian-type metamorphism overlapped in time with the onset of doming. New 87Rb/87Sr biotite ages from this same complex combined with previously published 87Rb/87Sr white mica ages suggest that doming and exhumation began no later than 28 Ma immediately in front of indenting Austroalpine crustal blocks, then migrated laterally to the ESE during rapid exhumation and orogen-parallel stretching beginning at about 23 Ma. Rapid cooling ended at approximately 17 Ma in the footwall of the Katschberg Normal Fault, which delimits the eastern margin of the Tauern Window. A similar pattern of migrating doming, orogen-parallel extension and cooling is recognized in the western part of the Tauern Window, where rapid exhumation began at about 20 Ma, some 2-3 Ma later than in the eastern part. This difference in the onset of rapid exhumation as well as the overall migration of doming from the center to the ends of the Tauern Window are attributed to fragmentation of the aforementioned Austroalpine blocks along the leading edge of the main Adriatic indenter (Southern Alps) as this indenter advanced to the north.