Apatite fission-track evidence for post-collisional exhumation of the Tauern Window, Austrian Alps
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Ten new apatite fission-track analyses from the Tauern Window, which includes some of the highest peaks in the Austrian Alps, reveal rapid exhumation in the Eastern Alps from 15 to 13 million years ago (Mya). The Alps were initially formed during the closing of the Tethys Ocean, from 60 to 30 Mya. During this time, however, the rocks currently exposed in the Tauern Window were buried at a depth of 35 km. These new data, with ages ranging from 17.4 (+3.7/-3.0) to 9.7 (+1.7/-1.4) Ma, confirm previous studies documenting renewed Miocene exhumation in the Alps, and indicate that the formation of the Tauern Window postdates the major mountain building episode. The mechanism of exhumation for the Tauern Window, however, remains unclear. Proposed exhumation mechanisms include north-south compression, extension during gravitational collapse, or post-collisional lateral extrusion. Previous studies (e.g. Most, 2003) suggest these rocks were at a depth of 10 km at ~16-14 Mya; these new fission-track data indicate that these rocks were at a depth of 3-4 km by ~13 Mya. Together, these data are consistent with an exhumation rate of 3 km/My from 15 to 13 Mya. This is a rapid exhumation rate, comparable to rates in the modern Himalaya, an area undergoing compression (e.g. Blythe et al., 2007), and in areas undergoing rapid extension, such as the Basin and Range during the mid-Miocene (e.g. Stockli et al., 2000). This study suggests that the Tauern Window was not exhumed by pure strike-slip motion, but may have been the result of localized rapid exhumation due to lateral extrusion of the Eastern Alps.