BGS Rock Classification Scheme
Contact metamorphic rock - Contact metamorphism results from the temperature perturbation associated with the emplacement of magma into the crust. The extent of the thermal perturbation will be determined by both the crustal level at which the magma was emplaced and the volume of the magma body; contact metamorphism will merge into regional metamorphism when a large body of magma is emplaced at greater depths. In many cases, contact metamorphism is not accompanied by recognisable tectonic effects, with the result that new mineral assemblages develop granoblastic textures. The amount of recrystallisation and the associated metamorphic mineral assemblages are largely a product of a combination of the heat energy available, nature and volume of fluid flow, lithology of the country rock and the distance from the heat source. A gabbroic magma is hotter than a granite magma and so would be expected to produce greater recrystallisation with higher temperature minerals. With increasing recrystallisation granoblastic textures progressively develop so that pre-existing features in the rock are destroyed, ultimately resulting in hard, fine- to medium-grained rocks lacking parting surfaces. Preexisting features such as schistose or gneissose textures may be recognised by lithological heterogeneities. British Geological Survey Research Report RR/99/02, section 9.6.
| Code | MRC |
|---|---|
| Description | Contact metamorphic rock - Contact metamorphism results from the temperature perturbation associated with the emplacement of magma into the crust. The extent of the thermal perturbation will be determined by both the crustal level at which the magma was emplaced and the volume of the magma body; contact metamorphism will merge into regional metamorphism when a large body of magma is emplaced at greater depths. In many cases, contact metamorphism is not accompanied by recognisable tectonic effects, with the result that new mineral assemblages develop granoblastic textures. The amount of recrystallisation and the associated metamorphic mineral assemblages are largely a product of a combination of the heat energy available, nature and volume of fluid flow, lithology of the country rock and the distance from the heat source. A gabbroic magma is hotter than a granite magma and so would be expected to produce greater recrystallisation with higher temperature minerals. With increasing recrystallisation granoblastic textures progressively develop so that pre-existing features in the rock are destroyed, ultimately resulting in hard, fine- to medium-grained rocks lacking parting surfaces. Preexisting features such as schistose or gneissose textures may be recognised by lithological heterogeneities. British Geological Survey Research Report RR/99/02, section 9.6. |
| Qualifiers | No qualifiers currently exist. |
| Definition | Not Available |
| Linked data | http://data.bgs.ac.uk/id/EarthMaterialClass/RockName/MRC |
CAVEAT
"Thumbnail" definitions attached to some of the table entries are an interim attempt to provide simple short descriptions of the "unqualified" rock types presented within the BGS Rock Classification Scheme. Every effort has been made to ensure accuracy and consistency but minor contradictions or omissions might be present. The BGS welcomes any feedback pointing out such minor imperfections and/or providing constructive comment and suggestions for improvement of the definitions. In the first instance such feedback should be directed to Dr Tim McCormick.