Metamorphic rock
Metamorphic rock or metamorphic rock is rock that is formed from a rock of any type due to an increase in ambient pressure or the ambient temperature relatively deep in the earth's crust. In this transformation, the solid state is maintained. The conversion process is called metamorphosis.
Formation
In comparison with other rock- changing processes such as chemical weathering or diagenesis, a rock metamorphosis takes place under considerable pressure and temperature conditions. The reason for this is often the formation of mountains or other with the plate tectonics more or less closely -related processes.
In the conversion, new minerals and mineral aggregates, whose pressure-and temperature-dependent education corresponds to the ambient conditions. However, the general chemical composition of a rock does not change when the metamorphosis, otherwise it is called metasomatism. At a pressure- stressed Metamorphose often occurs an orientation of the mineral grains in the rock, which represents, which was carried out directions of the largest pressure. This changes the stone structure (eg, texture), which differ in terms of their metamorphic structure of chemically similar, also produced in the earth's crust plutonic rocks.
Nomenclature
In contrast to the igneous rock and sedimentary rock, there is no uniform nomenclature for metamorphic rocks. In practice, different nomenclature systems are used side by side.
Starting from the protolith
Is this unmetamorphe parent rock ( protolith ) of a Metamorphites recognizable, the name of the Protoliths the prefix is simply meta- prefixed, such as in metabasalt or metagreywacke.
Based on the rock fabric
The microstructure and thus the corresponding names reflect whether the metamorphosis was associated with tectonic movements, or not. However, in some cases is also the content of minerals of a particular class mineral crucial for this nomenclature.
- As a massive rock metamorphic rocks are referred to without preferred orientation of the mineral grains. Although a harness is not uncommon, but goes back to the primary layering of sedimentary Protoliths. As " clif " called metamorphic rocks occur in contact and immersion metamorphoses.
- All of the following terms refer to rocks whose names relevant structure dates back to tectonic deformation: The term gneiss indicates medium-to coarse-grained metamorphic rock with a relatively wide continuous parallel structure. An additional criterion is a high proportion of feldspars (over 20 %). In gneisses, there is also a rough breakdown by source rock: orthogneiss for a non- sedimentary source rock and paragneiss for a " vergneistes " non- carbonatic sedimentary rocks. Granulite gneiss is a texturally closely related rock that but differs from the mineral constituents by high- jerk minerals such as garnet and the absence of muscovite mica and general poverty.
- " Slates " are very fine-grained slate, which have only undergone a very low grade or even garkeine metamorphosis, and therefore in effect still have their original mineral constituents. A typical example is the mostly dark Paleozoic shales of many German low mountain range. They are not to be confused with " schist " trained mudstones that were exposed solely to diagenetic processes without significant tectonic deformation, such as the Posidonia Shale of the Black Jura or the copper schist of the Zechstein (these are called in English " shale" ).
- Medium-to coarse-grained slate ( " crystalline schists ") with a relatively high metamorphic grade and, therefore, comprehensive mineral transformations are referred to as " Schist ".
The rock names especially the gneisses and crystalline slate to be further specified by prefixing the names of minerals, containing the corresponding rocks in larger proportions. The minerals are sorted in ascending order of frequency. For example, a sillimanite - garnet - mica schist contains more mica than garnet and garnet more than sillimanite.
Migmatite is the name for a rock that is characterized by a flow texture as a result of partial melting ( anatexis ). As metamorphosis proceeds, by definition, without partial melting, migmatites lead over to the igneous rocks.
Based on the mineral constituents
The most commonly used names are here:
- Amphibolite, a predominantly composed of amphibole and plagioclase rock
- Eclogite, an operation preceded by a high garnet and Klinopyroxenanteil high-pressure rocks
- Marble, metamorphic carbonate rocks consisting mainly of calcite or dolomite in accordance
- Quartzite, metamorphic quartz sandstone, which consist mainly of quartz according to
- Serpentinite, a predominantly from existing Serpentinmineralen metamorphic
Other Benamungen
In addition, there are further terms which the structure nor the mineral inventory classification can be identified with neither. Thus, the term "fruit shale " a kontaktmetamorphes rock, whose slate-like structure was not produced, as in "real" slates by tectonic By moving, but is a relic of the primary layering of the rock.