Slab Break-offs in the Alpine Subduction Zone

Abstract

Abstract. After the onset of plate collision in the Alps, tectonic processes are inferred to have changed dramatically in the Alps: European plate break-offs in various places of the Alpine arc, as well as a subduction polarity reversal in the eastern Alps have been proposed. We review body-wave tomographic studies, compare them to our surface-wave-derived model, and interpret them in terms of slab geometries. We infer that the shallow subducting portion of the European plate is likely detached under both the western and eastern (but not the central) Alps. The Alps-Dinarides transition may be explained by a combination of European and Adriatic subduction. This implies that the deep high-velocity anomaly (> 200 km depth) mapped by tomographers under the eastern Alps is a detached segment of the European plate. The shallower fast anomaly (100–200 km depth) can be ascribed to European or Adriatic subduction, or both. These findings are compared to previously proposed models for the eastern Alps in terms of slab geometry, but also integrated in a a new, alternative geodynamic scenario that best fits both tomographic images and geological constraints.

Large-wavelength late Miocene thrusting in the North Alpine foreland: Implications for late orogenic processes

“…1 and 9; Qorbani et al, 2015). Although the tomographic data have been interpreted in different ways regarding the slab geometries at depth (Kästle et al, 2019;Lippitsch et al, 2003;Mitterbauer et al, 2011;Zhao et al, 2016), most of them concur on the observation that between the deep velocity anomalies of the Central and the Eastern Alps a major discontinuity is present east of the Giudicarie and Brenner Faults (see also Handy et al, 2015). This correlates with the eastward termination of the Miocene Subalpine Molasse near Salzburg (Fig.…”

“…12.5° E, i.e. the area of Salzburg, while farther east, a segmentation of the slab structure is observed (Kästle et al, 2019;Lippitsch et al, 2003;Mitterbauer et al, 2011;Zhao et al, 2016; see further details in the discussion section). Classically, the boundary (or transition) between the Central and the Eastern Alps has been located in eastern Switzerland where remnants of the Piemont-Ligurian Ocean separate units deriving from the former European passive margin (Central and Western Alps) from units deriving from the Adriatic Plate north of the Insubric Line (Figs.…”

“…(iii) The proposed segmentation of the deep structure of the Central and Eastern Alps (i.e. slab detachment and subduction polarity reversal; Handy et al, 2015;Kästle et al, 2019;Kissling et al, 2006;Lippitsch et al, 2003;Mitterbauer et al, 2011;Schmid et al, 2004), which is expected to have induced a geodynamic and tectonic reorganization along the Alpine chain by the end of mid-Miocene times could explain the subsequent late Miocene tectonism restricted to the foreland of the Central Alps until ca. Salzburg and thus decoupled from the Eastern Alps.…”

“…At the lithospheric scale, a polarity reversal between the European slab and the Adriatic slab has been conjectured beneath the western Tauern Window (Lippitsch et al, 2003). However, this model is currently debated as new geophysical data indicate that at depth the southward dipping European slab extends from the Central Alps until east of the Giudicarie and Brenner Faults (Kästle et al, 2019) and possibly as far east as 12.5° E, i.e. the central Tauern Window (Figs.…”

Slab Rollback Orogeny model for the evolution of the Central Alps: Seismo-Thermo-Mechanical test

“…1b), while along a N-S transect at ∼10 • E longitude the slab hangs in a sub-vertical position beneath the core of the Alps (Lippitsch et al, 2003). Furthermore, a recent review of different high-resolution tomographic studies combined with shear-and bodywave models show that at depths of 250 km, the slab in the Central Alps becomes indistinguishable, thus leading to the conclusion that a breakoff is likely at a depth of roughly 250 km (Kästle et al, 2019). If the scenario proposed by Lippitsch et al (2003) holds, the SRO model might offer an explanation for the current seismicity pattern across the Central Alps (Fig.…”