Cataclasite under a petrographic microscope. A petrographic microscope is a Microscope used in Petrology and Optical mineralogy to identify rocks and Minerals in Thin sections The rock in part of the Malm-formation of the Helvetic nappes; sample found in a landslide near Engelberg in the Swiss Alps. (population 1800 is the administrative centre of the municipality of Verran in the county of Nord-Trøndelag, Norway. The Helvetic nappes (Helvetische Decken are a series of Nappes in the Northern part of the Alps and part of the Helvetic zone. A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur Engelberg is a municipality in the canton of Obwalden in Switzerland. The Swiss Alps (Schweizer Alpen Alpes suisses Alpi svizzere Alps svizras are the central portion of the Alps Mountain range that lies within

Cataclasite is a metamorphic rock that is formed by mechanical shear stress during faulting ^[1]. Metamorphic rock is the result of the transformation of an existing rock type the protolith, in a process called Metamorphism, which means "change A shear stress, denoted \tau\ ( Tau) is defined as a stress which is applied Parallel or tangential to a face of a material In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement It is either incohesive or cohesive with poor schistosity. Cohesion is the component of shear strength of a rock or Soil that is independent of interparticle Friction. It is usually non-foliated and consists of angular clasts in a finer-grained matrix. Foliation is any penetrative planar fabric present in rocks. Foliation is common to rocks affected by regional metamorphic compression typical of orogenic Clastic rocks are composed of fragments or clasts, of pre-existing rock. The matrix or groundmass of rock is the fine-grained mass of material in which larger grains or Crystals are embedded ^[2]

Types of cataclasite

There are many varieties of cataclasite, classified by the percentage of the volume formed from the matrix. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically

Protocataclasite

Protocataclasite is a type of cataclasite in which the matrix takes up less than 50% of the total volume.

Mesocataclasite

Mesocataclasite is a type of cataclasite in which the matrix occupies between 50 and 90 percent of the total volume.

Ultracataclasite

Ultracataclasite is a type of cataclasite characterized by a matrix occupying greater than 90% of the total volume.

Foliated Cataclasite

Foliated cataclasite is a type of cataclasite with a significant content of clay. Grades through to fault (clay) gouge when the proportion of clay is greater than 70%. Fault gouge is an unconsolidated Tectonite (a rock formed by tectonic forces with a very small grain size

Fault Breccia

Fault breccia is a medium to coarse-grained cataclasite.

Formation

Cataclasite forms by the progressive fracturing of mineral grains and aggregates, a process known as cataclasis. A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition a highly ordered atomic structure and specific The fracturing continues until a distribution of clast sizes is developed that allows the sliding of clasts past each other, without high enough frictional stresses to further fracture the rock significantly. From then on deformation is accommodated by continued sliding and rolling of fragments, a deformation mechanism known as cataclastic flow. In Structural geology, Metallurgy and Materials science, deformation mechanisms refer to the various mechanisms at the grain scale that are responsible In poorly consolidated or unconsolidated sediments, deformation in fault zones also occurs by rolling and sliding of grains but the porosity of the rock accommodates the resulting strains without significant grain fracturing.

References

1. ^ Oilfield Glossary
2. ^ British Geological Survey