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Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock that was reconstituted subsequently by partial melting ("neosome"), while the alternate layer has a ...
Migmatite is a gneiss consisting of two or more distinct rock types, one of which has the appearance of an ordinary gneiss (the mesosome), and another of which has the appearance of an intrusive rock such pegmatite, aplite, or granite the (leucosome). The rock may also contain a melanosome of mafic rock complementary to the leucosome. [11]
Younger metasediments are found in the southwest and northwest in synclinorial schist belts. Compared to the surrounding migmatite-gneiss complexes, these low-grade metamorphic rocks have isoclinal folding and steeply dipping foliation. They have faulted and sheared boundaries with the surrounding rock.
The oldest Precambrian rocks in Wisconsin are late Archean quartzofeldspathic gneiss, migmatite and amphibolite up to three billion years old and igneous rock such as the granite of the Puritan Quartz Monzonite. Mafic and intermediate metavolcanic rocks together with metasedimentary rocks are found in the Ramsey Formation in Iron County and ...
These Archean rock formations tend to also include quartz diorite, acid and intermediate granulites and less commonly, basic granulites. Aruan Group rocks overly the Watian Group in the West Nile area, with biotite gneiss, hornblende gneiss, migmatite and granitic gneiss and quartzites.
Svecofennian migmatite rock outcrop on the island of Berghamn in the municipality of Pargas. The lighter parts of the outcrop are granite and the darker parts are mica schist. The southwestern part of Finland is mainly made up of rocks of the Svecofennian Domain or Svecofennian orogen. [10] These rocks are invariably of Proterozoic age.
Mylonite is a fine-grained, compact metamorphic rock produced by dynamic recrystallization of the constituent minerals resulting in a reduction of the grain size of the rock. Mylonites can have many different mineralogical compositions; it is a classification based on the textural appearance of the rock.
The minerals present in a granulite will vary depending on the parent rock of the granulite and the temperature and pressure conditions experienced during metamorphism. A common type of granulite found in high-grade metamorphic rocks of the continents contains pyroxene, plagioclase feldspar and accessory garnet, oxides and possibly amphiboles.