Critical taper behaviour and out‐of‐sequence thrusting on orogenic wedges – an example of the Eastern Alpine Molasse Basin

Abstract

We demonstrate that increasing erosion during the kinematic evolution of a thrust wedge will lead to out-of-sequence thrusting as a result of backwards critical taper movement. In-sequence Accepted ArticleThis article is protected by copyright. All rights reserved. thrusting in the Subalpine German Molasse Basin built a critical-tapered foreland Coulomb thrust wedge. Later out-of-sequence thrusts dissected all but the frontal duplex stacks. The footwall/hangingwall relation visible on seismic data proves the out-of-sequence nature of the latest thrusting stage. Establishing a stable drainage system leads to increased erosion in elevated areas of the thrust wedge, resulting in flattening of the critical wedge. In order to keep its predefined angle, the critical wedge repositions, and the tip of the taper moves towards the hinterland. Thus, thrusting will also reposition and move towards the hinterland.

Late Miocene thrusting in the North Alpine foreland: Driven by a deep-seated process and shaped by the local mechanical stratigraphy

“…Since the youngest AHe ages are associated with internal tectonic slices of the Subalpine Molasse (Figs. 2, 3, and 4), we can infer the occurrence of break-back thrusting, a characteristic feature, which has been confirmed along the entire Subalpine Molasse of the Central Alps based on thermochronological data and cross section restoration (von Hagke et al, 2012(von Hagke et al, , 2014Ortner et al, 2015;Schuller et al, 2015), but has been argued for as early as the 1930s (Haus, 1935(Haus, , 1937. The break-back thrusts are supposedly younger than the development of the frontal triangle zone, which formed the active northern deformation front from ca.…”

“…The latter consists of south-dipping imbricated thrust sheets and in large parts north-dipping backthrusts forming a triangle zone at the transition to the Plateau Molasse ( Fig. 1b; Berge and Veal, 2005;Fuchs, 1976;Müller et al, 1988;Ortner et al, 2015;Schuller et al, 2015;Sommaruga et al, 2012). The Subalpine Molasse started to become incorporated into the orogenic wedge shortly after deposition in Oligocene times (Hinsch, 2013;Kempf et al, 1999;Pfiffner, 1986).…”

“…Recently, new studies have documented that the Subalpine Molasse was subject to break-back thrusting between ca. 13 Ma and4 Ma (von Hagke et al, 2012, 2014;Ortner et al, 2015;Schuller et al, 2015), which was thus coeval to folding and thrusting in the Jura FTB.…”

“…6; e.g. Berge and Veal, 2005;Müller et al, 1988;Schuller et al, 2015;Sommaruga et al, 2012;Stäuble and Pfiffner, 1991). The Aare valley, running across the study area, is characterized by a low relief and is filled by >100 m-thick Quaternary deposits ( Fig.…”

A review on out-of-sequence deformation in the Himalaya

“…They deciphered a significantly high c. 12 mm a 21 slip rate and a c. 7 mm a 21 rate of shortening in the horizontal direction from this out-of-sequence thrust during the Holocene. De Sarkar et al (2014) concluded that profound erosion and a critical taper condition produced this out-of-sequence thrust (see also Schuller et al 2015). However, debate has not resolved about how far erosion can control the (Himalayan) tectonics (see brief review in Whipple 2014).…”