Window (geology)

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Tectonic window (F) in a schematic profile section (black: land surface). The ceiling shown in white was removed by erosion in a limited area (red dashed line: former ceiling lower limit), in the window is the one shown in red

As a window or tectonic window in which is geology a by erosion or horizontal crustal exposed ( ausbeißender , often at high altitudes more open ) part of the base of a tectonic ceiling designated. Tectonic windows often occur in those fold mountains whose structure (tectonics) is strongly characterized by shallow thrusts (ceiling thrusts or ceiling construction). Prime examples of tectonic windows can be found in the Lower Engadine window and the Tauern window in the Alps.

Geological construction

Elements of a thrust system: cliff , window, ceiling , thrust

Tectonic windows are openings or gaps in a spacious thrust nappe . Inside the window, the rocks pushed over by the ceiling emerge. A tectonic window thus allows - analogous to a "real" window - the insight into the local geological subsurface.

The rocks in the window are tectonically deeper than those in the ceiling - they form what is tectonically lying in the common rock complex of ceiling and window . Conversely, the ceiling rocks are tectonically higher than the rocks of the window - they form the tectonically hanging wall in the common rock complex of ceiling and window and, based on the term window, are also referred to as frame rocks . As a rule, the rock of the ceiling in direct contact with the tectonically lying surface is older than the lying surface. The mean age of the ceiling does not have to be higher than that of the overturned rock complex.

One speaks of a half-window when the ceiling does not enclose its erupting bedrock on all sides. We speak of a double window when a window breaks through not just one, but two ceilings lying one above the other.

The counterpart to the tectonic window is the tectonic cliff . The distance between a cliff and a window indicates the minimum thrust distance.

Examples from the Eastern Alps

Geological map of the Lower Engadine window

In mountains - especially young fold mountains - windows are often found in the core of large anticline structures (large saddles).

The two largest and most famous windows in the Eastern Alps are the Lower Engadine window ( Graubünden / Tyrol ) and the Tauern window ( Salzburg / Carinthia ). Smaller windows are in the west u. a. the Gargellenfenster ( Vorarlberg ), east the Semmering window ( Steiermark / Lower Austria ) and at the Hungarian border the Rechnitz window .

literature

  • GH Eisbacher (1996): Introduction to Tectonics. Enke publishing house, Stuttgart. ISBN 3-432-99252-1
  • T. Labhart (2001): Geology of Switzerland. Ott Verlag, Thun. ISBN 3-7225-6762-9