Northern Calcareous Alps

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 Alpenseminar by Julian Welte



On the 18th of May, we discussed about the nappe structure of the Northern Calcareous Alps and its disintegration during Miocene tectonic extrusion, given by Mr. Welte.

The Northern Calcareous Alps includes the following succession of nappes from north to south, and from bottom to top(see Alpine Tectonics map, purple coloured ):
Bavarian nappes(Mesozoic cover), with narrow synclines and anticlines.
Toward the south they dip down below the overthrusted Tyrolic nappe complex. Due to their dominant dolomitic lithology, the Tyrolic nappes exhibit internal thrusting and faulting and only minor folding.
The Juvavic nappes represent the uppermost tectonic element, overlying the Tyrolic nappes.



The nappe complex of the Northern Calcareous Alps (after PLÖCHINGER, 1995). (GERHARD W. MANDL, 2000)

Explanation of abbreviations: Northern Calcareous Alps: Juvavic nappes: B = Berchtesgaden nappe, D = Dachstein nappe, SC = Schneeberg nappe, H = Hallstatt units, M = Mürzalpen nappe, GL = Göll-Lammer unit. Tyrolic nappes: K = Krabachjoch nappe, I = Inntal nappe, SH = Stauffen-Höllengebirge nappe, TG = Totengebirge nappe, W = Warscheneck unit, SZ = Werfen imbricated zone' RA = Reisalpen nappe, G = Göller nappe, U = Unterberg nappe. Bajuvaric nappes: L = Lechtal nappe, R = Reichraming nappe, S = Sulzbach nappe, Lu = Lunz nappe, A = Allgäu nappe, T = Ternberg nappe, F = Frankenfels nappe, c = basal slices. Penninic units: O = Arosa zone, w = windows of the Rhenodanubian Flysch zone.

The succession of Mesozoic sediments of the NCA has largely lost its former crustal basement in the course of the Alpine orogeny. During Late Jurassic to Tertiary times, several stages of deformation (folding and thrusting) created a nappe complex which rests with overthrust contact on the Rhenodanubian Flysch Zone in the north and on Variscan basement (Greywacke Zone) in the south.


Profiles (ca. NW–SE) showing evolution of the Central Northern Calcareous Alps between Upper Jurassic and Eocene times. Frisch & Gawlick (2003)

-  Late Middle to Upper Jurassic:  destruction of the Tethys continental margin by nappe thrusting and progradation from the oceanic side towards the shelf.
- Early Cretaceous: nappe thrusting prograded towards the inner shelf and incorporated the Bavaric unit into the nappe stack. Reactivation of Upper Jurassic tectonic features occurred, and metamorphic overprint affected parts of the Tirolic unit.
- Cenomanian or Turonian time: Thrusting arrived at the northern margin of the NCA.
- After deposition of the Turonian to Eocene Gosau Group, the northern parts of the NCA nappe stack were thrust over the Rhenodanubian Flysch. 
- Early to Middle Miocene: lateral tectonic extrusion caused block segmentation and rearrangement of the block puzzle along a conjugate fault system. The elongated shape of the NCA and the entire Eastern Alps was attained during this tectonic phase.

Cross sections across the eastern part of the Alpine orogen from Miocene to Present Mark R. Handy · Kamil Ustaszewski · Eduard Kissling(2005)
a 20 Ma: Indentation of eastern Adriatic crustal indenter, foundering of European slab, incipient northward subduction of Adriatic lithosphere derived from the Eastern and Southern Alps;
b Present section at about 13°E with north-dipping Adriatic slab beneath the Tauern Window.

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