Cataclasite
Cataclasites are hard rocks with mostly directionless-chaotic structure , the sunburst-like deformation and dynamic Re crystallization has arisen due to tectonic stress. The process is known as a cataclase . Cataclasites and genetically similar rocks are grouped under the generic term rocks with deformation structures or cataclastic rocks .
General
As a result of tectonic processes, discrete fracture surfaces , so-called fault or fault surfaces, arise in the mountains at relatively low temperatures . As a result of the movements, the rock at the fault areas is sometimes heavily stressed mechanically. As a result, it can become fragmented and downright ground up. This mechanical destruction also affects the individual mineral grains (“crystals”) in the rock. At increased temperatures in greater depths of the crust, a new formation of very small mineral grains takes place through so-called dynamic recrystallization (crystallization in rock that is moving through). The resulting structure is called the deformation structure . "Real" cataclasites are formed at slightly higher temperatures at the transition from purely friable to plastic deformation . Cataclasites among the low grade metamorphic rocks and differ in by the other rocks with deformation structure, the primary-unconsolidated Kakiriten ( Störungsbrekzien , Ruscheln , disorder Letts ), which are in fact unmetamorph, and mylonites , which, apart from mylonitisierten Evaporitgesteinen , medium to highly metamorphic are.
Properties and subdivisions
The term cataclasite refers exclusively to the structure, grain binding and genesis of the rock and is in fact independent of the mineral composition. Depending on the intensity of the mechanical stress and the resulting structure, a distinction is made between protocataclasites , cataclasites and ultracataclasites . In the case of protocataclasites, the degree of comminution is still moderate and numerous grains can still be seen with the naked eye, with a matrix content of 10 to 50%. In cataclasites it is already stronger (matrix share 50–90%) and in ultracataclasites it is very strong (more than 90% matrix). In ultra- cataclasites in particular, so-called cataclastic flow can cause foliation ("foliation").
literature
- Peter Heitzmann: Kakirite, Kataklasite, Mylonite - On the nomenclature of metamorphic rocks with deformation structures . In: Eclogae Geologicae Helvetiae . tape 78 , no. 2 , 1985, pp. 273-286 , doi : 10.5169 / seals-165656 .
- Wolfhard Wimmenauer : Petrography of igneous and metamorphic rocks . Enke, Stuttgart 1985, ISBN 3-432-94671-6 , pp. 311 ff .
- Roland Vinx: Rock determination in the field . Munich 2005, ISBN 3-8274-1513-6 .