Metamorphic core complex
As Metamorphic Core Complex (English metamorphic core complex) is in geology refers to a section of land, occur in the originally low-lying in the earth's crust, highly metamorphic rocks in the midst of much lower or non- metamorphic rocks to light. The emergence of these areas is based on extensional and takes place largely without Magmenbildung.
The process passes through the middle and lower continental crust to the surface is relatively developed rapidly. During the stretching operation, flat-lying shearing arise, which are formed as mylonitische shear zones. Below this high-grade metamorphic rocks are Abscherhorizonte from the eclogite, granulite or amphibolite facies, which were ductile deformation. The rocks in the hanging wall were to greenschist facies during this movement operations ( synkinematisch ) or converted to amphibolite facies metamorphic rocks, their deformation behavior was ductile - brittle to brittle.
Descriptions / definitions
Coney (1980 ) defined metamorphic core complexes as follows:
» The metamorphic core complex is generally characterized as a heterogeneous basement Terran, which is composed of older metamorphic and plutonic rocks and is overprinted by a younger mylonitschen or gneiss -like texture with flat-lying foliation and lineation. The covering Terran in the hanging wall is present in unmetamorphosierten condition and is from a system of countless relatively flat-lying faults with expiring younger fault branches to the elderly, dismembered and consequently stretched. Between the basement and the cover is a Terran Abscherhorizont and / or a steep increase in metamorphic grade. Walking Along brecciation and other kinematic and structural evidence suggest that sliding or shearing movements. "
The Abscherhorizont is called décollement and detachment in English as in French.
Lister and Davis ( 1989) give the following definition:
" The formation of metamorphic core complexes results from the large-scale expansion of the continental crust. The middle and lower crust is literally pulled below the aufreißenden and the extending upper crust. The required movement horizons subject to a spatial and a temporal development. The deformed rocks in the footwall experienced a gradual upward movement, which allows them to pass through different metamorphic and structural facies and they consequently imparts a characteristic sequence at Meso - and microstructures. "
Occurrence
The concept of the metamorphic core complex was first developed in the Cordillera of western North America, which houses numerous examples:
- In Canada (British Columbia): Shuswap Highland
- In the United States Arizona Buckskin Mountains - Rawhide Mountains, Pinaleno Mountains, Santa Catalina Mountains, Rincon Mountains and South Mountains
- Idaho: Albion Mountains and Pioneer Mountains
- California: Whipple Mountains
- Montana: Anaconda Range and Bitterroot Mountains
- Nevada: Ruby Mountains and Snake Range ( south )
- Washington: Okanagan Highland
The deposits in the northern Cordillera derived from the Eocene, whereas the further south located (for example, in Arizona) are more recent.
Metamorphic core complexes are not only restricted to North America, they also occur in Anatolia, Iran, Tibet or in New Zealand. The geologically youngest metamorphic core complex is located in eastern New Guinea ( D' Entrecasteaux Islands).
Other occurrences of metamorphic core complexes can also be found in:
- Austria: Rechnitz window, Styria / Burgenland
- China: number of core complexes in the Yinshan - Yanshan mountain range Taihan ( Hohhot, Yunmen, Fangshan, Dushan, Malanyu, Fuping and Zanfang )
- Germany: Saxon Granulitmassiv north of Chemnitz
- France: Montagne Noire
- Greece: Naxos, Paros, Evia, Andros, Tinos, Mykonos, Ikaria, Ios, Thassos, southern Rhodope Mountains, Mount Olympus, Crete and Serifos
- Italy: Monticiano - Rocca Strada in Tuscany and the peninsula of Calamita on Elba
- Cuba: Escambray massif
- Namibia: Sinclair complex at Lüderitz
- Norway: Western Gneiss Region
Metamorphic core complexes were identified even in the oceanic area, first in the Atlantic. Since then, a further number of these structures was discovered in the oceanic lithosphere, mostly at mid-ocean ridges with intermediate, slow and ultra- slow Spreizgeschwindigkeit, but also in backarc basins, such as the Mid-Atlantic Ridge and the Southwest Indian ridge. Some of these oceanic metamorphic core complexes were drilled and sampled. The works show that they primarily of mafic and ultramafic rocks ( gabbro and peridotite, but also dolerite ) are constructed in the footwall. The Abscherhorizont is relatively thin and consists of hydrous phyllosilicates. Oceanic metamorphic core complexes are often associated with active hydrothermal fields in combination.
Extraterrestrial occurrences
A structure in the center of Artemis Corona on Venus was interpreted by Spencer (2001) as a metamorphic core complex. It could be the largest metamorphic core complex in the solar system here quite.