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Blueschist on Île de Groix, France Photomicrograph of a thin section of blueschist facies metamorphosed basalt, from Sivrihisar, Turkey. Blueschist (/ ˈ b l uː ʃ ɪ s t /), also called glaucophane schist, is a metavolcanic rock [1] that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (200–500 °C (392–932 °F ...
The geology of Anglesey, the largest (714 km 2) island in Wales is some of the most complex in the country. Anglesey has relatively low relief, the 'grain' of which runs northeast–southwest, i.e. ridge and valley features extend in that direction reflecting not only the trend of the late Precambrian and Palaeozoic age bedrock geology but also the direction in which glacial ice traversed and ...
Greenstones, aside from containing basalts, also give rise to several types of metamorphic rocks which are used synonymously with 'metabasalt' et cetera; greenschist, whiteschist and blueschist are all terms spawned from the study of greenstone belts. The West African early Proterozoic greenstone belts are similar to the Archean greenstone belts.
Blueschist is a rock typical for present-day subduction settings. The absence of blueschist older than Neoproterozoic reflects more magnesium-rich compositions of Earth's oceanic crust during that period. [81] These more magnesium-rich rocks metamorphose into greenschist at conditions when modern oceanic crust rocks metamorphose into blueschist ...
The greenstone belts of the various Archean cratons are commonly altered to the greenschist facies. These ancient rocks are noted as host rocks for a variety of ore deposits in Australia, Namibia and Canada. Greenschist-like rocks can also be formed under blueschist facies conditions if the original rock contains enough magnesium.
Hope Bay greenstone belt (Nunavut) Hunt River greenstone belt (Newfoundland and Labrador) Nuvvuagittuq Greenstone Belt (Quebec) Red Lake greenstone belt (Ontario) Rice Lake greenstone belt (Manitoba) Swayze greenstone belt (Ontario) Temagami Greenstone Belt (Ontario) Yellowknife greenstone belt (Northwest Territories)
Paired metamorphic belts are the product of subducted colder crustal rocks, which are taken to depth, metamorphosed and then exhumed. [1] However, if the rock unit is not exhumed relatively quickly after subduction ceases, the rock unit will re-equilibrate to the standard geothermal gradient and the geological record will be lost.
The mélange zones in the Franciscan usually have a block in matrix appearance with higher grade metamorphic blocks (blueschist, amphibolite, greenschist, eclogite) embedded within the mélange matrix. [16] The matrix material of the mélanges are mudstone or serpentinite. Geologists have argued for either a tectonic or olistostormal origin. [17]