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

Hugo Ortner,Sinah Kilian

doi:10.1007/s00531-021-02128-3

Hugo Ortner, Sinah Kilian

Open Access

https://doi.org/10.1007/s00531-021-02128-3

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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.

Highlights

The Northern Calcareous Alps (NCA) are the most northern and external part of the fartravelled Austroalpine nappe system of the Eastern Alps, and are a typical thin-skinned fold-and-thrust belt (e.g., Linzer et al 1995; Eisbacher and Brandner 1996; Schmid et al 2004)
In the western NCA; facies boundaries turn toward a N–S direction (Fig. 1b), and all units stacked have the same facies of an inner continental margin (Bechstädt and Mostler 1976; Tollmann 1976a; Haas et al 1995)
Based on the work of Ampferer and Hammer (1911) and Ampferer (1912), the western NCA have been subdivided into three major thrust sheets (Figs. 2, 3b): These are, from base to top, the (1) Allgäu thrust sheet, forming a narrow band at the northern margin of the NCA, except in the far west, the (2) Lechtal thrust sheet, representing the main body of the western NCA, and the (3) Inntal thrust sheet in the south-central part of the NCA of Tirol (Heißel 1958; Tollmann 1970b, 1976b; Eisbacher and Brandner 1996)

Summary

Introduction

The NCA are the most northern and external part of the fartravelled Austroalpine nappe system of the Eastern Alps, and are a typical thin-skinned fold-and-thrust belt (e.g., Linzer et al 1995; Eisbacher and Brandner 1996; Schmid et al 2004). In three seminal papers Hahn (1912, 1913a, b) subdivided the NCA from external to internal and base to top into the Bajuvaric, Tirolic, and Juvavic nappe systems (Fig. 1) 2, 3b): These are, from base to top, the (1) Allgäu thrust sheet, forming a narrow band at the northern margin of the NCA, except in the far west, the (2) Lechtal thrust sheet, representing the main body of the western NCA, and the (3) Inntal thrust sheet in the south-central part of the NCA of Tirol (Heißel 1958; Tollmann 1970b, 1976b; Eisbacher and Brandner 1996). Even if the sedimentary succession of the Inntal- and Krabachjoch thrust sheets is similar to the underlying Lechtal thrust sheet, these have been regarded to be part of the Tirolic nappe system, while the CRS, the Lechtal- and Allgäu thrust sheets have been interpreted as a part of the Bajuvaric nappe system (Hahn 1913a; Tollmann 1976b)

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