Thrust tectonics in the Wetterstein and Mieming mountains, and a new tectonic subdivision of the Northern Calcareous Alps of Western Austria and Southern Germany

Abstract

We investigate the tectonic evolution of the Wetterstein and Mieming mountains in the western Northern Calcareous Alps (NCA) of the European Eastern Alps. In-sequence NW-directed stacking of thrust sheets in this thin-skinned foreland thrust belt lasted from the Hauterivian to the Cenomanian. In the more internal NCA major E-striking intracontinental transform faults dissected the thrust belt at the Albian–Cenomanian boundary that facilitated ascent of mantle melts feeding basanitic dykes and sills. Afterwards, the NCA basement was subducted, and the NCA were transported piggy-back across the tectonically deeper Penninic units. This process was accompanied by renewed Late Cretaceous NW-directed thrusting, and folding of thrusts. During Paleogene collision, N(NE)-directed out-of-sequence thrusts developed that offset the in-sequence thrust. We use this latter observation to revise the existing tectonic subdivision of the western NCA, in which these out-of-sequence thrusts had been used to delimit nappes, locally with young-on-old contacts at the base. We define new units that represent thrust sheets having exclusively old-on-young contacts at their base. Two large thrust sheets build the western NCA: (1) the tectonically deeper Tannheim thrust sheet and (2) the tectonically higher Karwendel thrust sheet. West of the Wetterstein and Mieming mountains, the Imst part of the Karwendel thrust sheet is stacked by an out-of-sequence thrust onto the main body of the Karwendel thrust sheet, which is, in its southeastern part, in lateral contact with the latter across a tear fault.

Salt Tectonics Versus Shortening: Recognizing Pre‐Orogenic Evaporite Deformation in Salt‐Bearing Fold‐And‐Thrust Belts on the Example of the Silica Nappe (Inner Western Carpathians)

“…In purely contractional settings, young‐on‐older thrusts may form by folding and subsequent out‐of‐sequence thrusting that displaces part of the syncline over part of the anticline. However, this requires a very specific geometry that does not occur often in nature (Ortner & Kilian, 2022; Pace et al., 2014). More frequently, the young‐on‐older thrusts may be attributed to contractional deformation localization along inherited extensional structures: when the reverse displacement during fault reactivation is less than the preceding normal slip, the total throw remains normal.…”

Oblique basin inversion leads to fold localisation at bounding faults: Analogue modelling of the Achental structure, Northern Calcareous Alps, Austria

“…Lithotypes consist of lagoonal, reefal and forereefal lime-and dolostones with a fossiliferous content of e.g., stromatolithes, oolites, calcareous algae and sponges; (Sausgruber 1994a) and their fragments. Although the Alpine Muschelkalk Group and Wetterstein limestone show a general thickness between 1000 to 120 >2200 m in the Achensee region (Sausgruber 1994b;Nagel et al 1976;Gruber et al 2022), cross sections in Gruber et al (2022) show a thickness up to 3500 m. These thickness variations are attributed to salt tectonics in the Triassic (see Ortner and Kilian 2022;Granado et al 2019;Kilian et al 2021). The Carnian Raibl event marks the abrupt termination of carbonate sedimentation on the Wetterstein platform (Hornung et al 2007;Krainer et al 2011).…”

“…3) Shortening related to Late Jurassic obduction of Neotethys oceanic crust onto the southeastern Apulian margin heralded inversion of this margin that culminated in Cretaceous orogeny (Schmid et al 2004;Stüwe and Schuster 2010). During Cretaceous orogeny the NCA were a typical thin-skinned fold-and-thrust belt at the external margin of 65 the Austroalpine orogenic wedge in lower plate position (Eisbacher and Brandner 1996;Ortner and Kilian 2022). 4) During the Late Cretaceous this wedge was transported toward the northwestern passive margin of the Apulian plate.…”

“…The basement units of the Austroalpine wedge show a clear separation between the Cretaceous and Paleogene stages (Froitzheim et al 1994), but synorogenic growth strata show continuous shortening within the NCA (Ortner , 2003aOrtner and Gaupp 2007;. The nappe structure of the NCA (Tollmann 1973;Hahn 1912Hahn , 1913bHahn , 1913aAmpferer and Hammer 1911;Ampferer 1912;Heißel 1958;Eisbacher and Brandner 1996;Tollmann 1970Tollmann , 1976 has recently been revised (Ortner 2016;Ortner and Kilian 2022). Consequently, the former Inntal and Lechtal thrust sheets have been 90 combined in the Karwendel thrust sheet (Figure 1a), which overthrusts the Tannheim thrust sheet (combined from the Allgäu thrust sheet, Puitentalzone and Karwendelschuppenzone) to the north (Ortner 2016;Ortner and Kilian 2022;Kilian and Ortner 2019).…”

“…The nappe structure of the NCA (Tollmann 1973;Hahn 1912Hahn , 1913bHahn , 1913aAmpferer and Hammer 1911;Ampferer 1912;Heißel 1958;Eisbacher and Brandner 1996;Tollmann 1970Tollmann , 1976 has recently been revised (Ortner 2016;Ortner and Kilian 2022). Consequently, the former Inntal and Lechtal thrust sheets have been 90 combined in the Karwendel thrust sheet (Figure 1a), which overthrusts the Tannheim thrust sheet (combined from the Allgäu thrust sheet, Puitentalzone and Karwendelschuppenzone) to the north (Ortner 2016;Ortner and Kilian 2022;Kilian and Ortner 2019). The Achental thrust (red line) is given for reference of location.…”