Abstract
AbstractNew structural and thermochronological (zircon and apatite fission track) data from the eastern most Alps highlight distinct deformation phases affecting the Austroalpine unit along a major sinistral strike‐slip fault system, the Mur‐Mürz fault (MMF). The data link deformation to vertical motions prior to, during, and after the main phase of lateral extrusion of the orogen. Zircon fission track ages document rapid (ca. 15 °C/Myr) and diachronous (eastward younging) cooling and rock exhumation during the latest Cretaceous to Paleocene. Subsequent regional Eocene to early Miocene cooling below the closure temperature of the apatite fission track system occurred at slow rates (ca. 2 °C/Myr), suggesting that the region was not subject to major surface uplift and erosion during that period. Fault kinematic analysis along the MMF document pre‐extrusion NNW‐SSE contraction, middle Miocene syn‐extrusion NE‐SW to NNE‐SSW directed shortening, and Late Miocene E‐W contraction. All phases are characterized by strike‐slip fault regimes. Formation of the complex MMF zone triggered the exhumation of small, fault‐bound crustal blocks within the fault zone as documented by middle Miocene apatite fission track ages. Overall, ages are similar on both sides of the fault suggesting that lateral extrusion along the MMF was not associated with significant differential vertical motions. Local Pliocene rock cooling and exhumation was probably related to the buttressing effect of the underthrust Bohemian basement spur. Whereas large‐scale, post‐extrusion surface uplift of the extruding crustal wedges, such as the “Styrian block,” must have been related to long‐wavelength deformation processes affecting the easternmost Alps.
Highlights
The Alpine orogenic belt in central Europe shows remarkable along‐strike differences in the distribution of the major tectonic units, its architecture and its tectonic evolution (e.g., Handy et al, 2010; Rosenberg et al, 2015; Schmid et al, 2004)
We have presented new zircon fission track (ZFT) and apatite fission track (AFT) cooling ages from the Eastern Alps east of the Tauern window together with a fault slip analysis along a major Miocene strike‐slip fault, namely, the Mur‐Mürz fault (MMF)
The integrated thermochronological data and field kinematics provide new insights in the tectonic evolution of the eastern Eastern Alps summarized in three consecutive time steps
Summary
The Alpine orogenic belt in central Europe shows remarkable along‐strike differences in the distribution of the major tectonic units, its architecture and its tectonic evolution (e.g., Handy et al, 2010; Rosenberg et al, 2015; Schmid et al, 2004). What makes the eastern part of the Alps unique is that it has been strongly influenced by processes operating at a high angle to the overall north‐south orientated plate convergence in this region, which started in the Oligocene These processes include subduction roll‐back along the Carpathian arc and associated opening of the Pannonian back‐arc basin (e.g., Horváth et al, 2006; and references therein). Ratschbacher, Frisch, et al (1991) emphasized a change of the deformation regime from compressive/transpressive at the Tauern window to transtensive/extensive when approaching the Pannonian basin As such extrusion of the easternmost fault block, “wedge 1” sensu.
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