Strike (geology)

Schematic representation of the parameters that define the position of a "geological surface" (planar) in space: blue = horizontal plane as a compass rose, red = surface to be defined, green = surface perpendicular to the horizontal plane along the north-south axis, z =  streak line , Z =  direction of stroke , σ = angle of stroke ,  F = direction of fall, φ = angle of fall.
Stroking and falling are always perpendicular to each other. Illustration on an inclined layer surface.

In geology, strike is the spatial orientation of the longitudinal axis of the outcrop of a rock, for example a layer or sequence of layers of sedimentary rocks , as shown in a geological map . Furthermore, the orientation of the longitudinal axis of a morphological full shape, for example a mountain range, is also referred to as this. The indication of the scanning direction also serves to precisely define the mounting position of geological surfaces such as bedding planes and bounding surfaces of rock and mineral passages (including bauwürdiger mineral raw materials such as coal seams or veins) and Verwerfungs- , fractured , and foliation surfaces , foliation and interfaces of zones same Degree of metamorphosis in contact metamorphosis .

Spatial position of surfaces

definition

In a geometric model, “stroke” is defined as the intersection (trace) of the geological surface with an imaginary horizontal surface. This line is streakline called. The spatial position of the streak line is defined by the streak angle that it forms with the north direction. The angle is measured from magnetic north (N) clockwise, i.e. towards east (E); for example N 35 °. If you do not want to specify the angle exactly, but only approximately, this case is called "NE-strike" or "NE-SW strike". The slope of the geological surface against the surface of the horizontal plane is called falling . The gradient is greatest along the fall line , perpendicular to the direction of strike. The angle between the horizontal plane and the fall line is the fall angle .

By specifying strokes and traps, the spatial orientation of any geological area is clearly defined. A specification like "035 / 20SE" means that the strike direction of the geological area deviates by 35 degrees from north (clockwise) and that the area dips at 20 degrees to the southeast. This form of indication is the traditional geological notation . A newer form is the so-called Clar notation (after Eberhard Clar ). Instead of the numerical value of the strike direction, it contains that of the fall direction and in the above case would be given as 125/20.

Determination with measuring instruments

A suitable instrument for measuring strike and fall is the structural compass . A stratameter was used previously .

General strokes in Central Europe

The four main strokes in Central Europe, shown in connection with the respective eponymous geographical objects: orange = Hercynian, red = Erzgebirge, blue = Rhenish, violet = Eggisch.

The strike directions of rock units or faults that predominantly occur in a specific region are referred to as general or main strike directions. In the regional geology of Central Europe north of the Alpine region, the terms Hercynian (in older literature also Hercynian ), Variscan ( Erzgebirge ) as well as Rhenish and Eggisch have established themselves in this regard .

The term Hercynian is derived from the ancient name Hercynia silva and refers to the west-north-west-east-south-east strike of the Harz north rim fault or the entire Harz floe. In older literature one finds the term Sudetian strike synonymously for the Hercynian strike direction , which refers to the ridge course of the Sudetes . Variscan and Erzgebirge (the latter derived from the course of the ridge of the Erzgebirge ), on the other hand, denote a stroke in a north-east-south-west direction. Both strike directions are characteristic of the Variscan tectonics of Central Europe.

Rheinisch refers to a strike in the north-northeast-south-southwest direction and is derived from the spatial position of the Upper Rhine Graben. Eggisch stands for a strike in north-north-west-south-south-east direction, which is derived from the ridge of the Egge Mountains in East Westphalia . These two strike directions are directly related to the post-variscan, so-called Saxon tectonics in the Mesozoic and Tertiary .

In southwest German literature, the term Danubian , derived from the direction of flow of the upper reaches of the Danube , is occasionally used, which stands for a swipe from southwest to northeast.

Individual evidence

1. ^ Manfred P. Gwinner: Geometric Basics of Geology. Swiss beard, Stuttgart 1965.
2. ^ Manfred Schöttle: Geotopes in Baden-Württemberg. (PDF; 1 MB) Glossary. Retrieved February 10, 2012 .

literature

• Günter Möbus: Tectonics . German publishing house for basic industry, Leipzig 1989, ISBN 978-3-342-00403-5 .
• Friedrich Bender: Applied Geosciences, Volume I: Geological Survey, Structural Geology, Structural Science, Soil Science, Mineralogy, Petrography, Geochemistry, Paleontology, Marine Geology, Remote Sensing, Economic Geology . Thieme, Stuttgart 1981, ISBN 978-3-432-91011-6 .
• Collective of authors: Basic geological knowledge . Ed .: Horst Roschlau, Hans-Joachim Haberkorn. 2nd Edition. German publishing house for basic industry, Leipzig 1977, p. 197 .