Breccia

A breccia or breccia ( from the Italian breccia: rubble, the term can be found repeatedly in Goethe ) is a rock composed of rock debris square shape, which lie in a fine-grained groundmass. Breccias are similar in structure to the conglomerates (eg, pudding stone), but in which in contrast to the rounded breccia rocks are enclosed in a binder. The grain size is larger than two millimeters, rocks with angular grains smaller grain size are referred to as Mikrobrekzie. Differences are breccias after their formation, such as in sedimentary, volcanic, diagenetic and tectonic breccias. Existence of the fragments of one rock type, the breccia is monomikt, there are different, then it is polymikt.

Sedimentary breccias

The formation of sedimentary breccias is usually done at a short distance from that place, to which has been the destruction of the starting material. This is derived from the coarse, angular shape of the caked fragments, as long transport routes run (eg as a sediment in rivers or glaciers ) usually in a rounding of the edges. Rise to the formation of a breccia is mostly a mass movement, such as in a landslide, a landslide or submarine debris masses against a reef.

When sagging or collapse of rock cavities as a result of leaching and Subrosion arise from the nachgestürzten material collapse, burglary or Auslaugungsbrekzien.

Since fanglomerates that are washed especially in desert areas during heavy rain from mountain slopes to the plains, often include more square or only slightly rounded clasts, they are sometimes referred to as Schlammbrekzien.

Volcanic breccias

Other common processes that enable formation of brecciation are explosion events such as volcanic eruptions. Here Eruptionsbrekzien form, or deposit still in volcanic vent called Schlotbrekzien. Are the coarse components embedded in tuff, one also speaks of Tuffbrekzien. The surface of lava flows zähflüssgen dissolves, by the flow movements and Autobrekziierung, often in block lavas on.

Diagenetic breccias

Less frequent are diagenetic breccias that form during the process of rock formation and solidification, the intra- formational breccias called. These are caused by the breaking of already solidified rock strata caused by earthquakes or the fact that already a solidified layer of rock - in many cases limestone - breaks caused by high pore water pressure due to increasing overlay with new sediment. Examples of this phenomenon can be found for example in the Middle Triassic of the Northern Calcareous Alps.

Tectonic breccias

Not infrequently breccias resulting from the breakup of rock due to a fault ( Reibungsbrekzie, Störungsbrekzie, Verwerfungsbrekzie, Gangbrekzie ). Tectonic breccias vary significantly according to formation conditions, especially temperature and pressure, different structures, which characterize certain Brekziengesteine ​​( fault gouge or Bruchbrekzie, cataclasite ).

Impaktbrekzien

The presence of breccias may be indirect evidence for an impact event in which a meteorite smashed the rocks and compacted by high pressures and has caked in some cases. In Germany such Impaktbrekzien come in the form of the Bunte breccia in the meteorite craters of the Ries and Steinheim Basin, for example.