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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 ("paleosome"), while the alternate layer has a ...
The mafic minerals in the TTG rock body, possibly biotite, were weathered, which introduced a brownish coating on the TTG rock surface. Tonalite–trondhjemite–granodiorite ( TTG ) rocks are intrusive rocks with typical granitic composition ( quartz and feldspar ) but containing only a small portion of potassium feldspar .
Because every mineral is stable only within certain limits, the presence of certain minerals in metamorphic rocks indicates the approximate temperatures and pressures at which the rock underwent metamorphism. These minerals are known as index minerals. Examples include sillimanite, kyanite, staurolite, andalusite, and some garnet. [15]
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 Migmatite-Gneiss Complex covers half of Nigeria's surface area and encompasses Archean gray gneisses, with tonalite and granodiorite consistencies. Within this complex are occurrences of schist , migmatite , garnet , sillimanite , kyanite and staurolite , which together indicate high-grade metamorphism up to the level of amphibolite on the ...
The rock record contains an uncertain age gap with younger 1.8 billion years old Proterozoic quartzofeldspathic and migmatite gneiss, with amphibolite and biotite schist. Around 1.9 billion years ago, mafic, intermediate and felsic rocks, in some cases with subordinate metasedimentary rocks, began to form and metamorphosed, reaching greenschist ...
Aruan Group rocks overly the Watian Group in the West Nile area, with biotite gneiss, hornblende gneiss, migmatite and granitic gneiss and quartzites. Karamoja Gneiss Group rocks share a very similar lithology to the Aruan Group, along with the eastern West Nile Mirian Group , although this group has experienced intense isoclinal folding.
Tethys Ocean, Tethyan sediments outcrop along the Tibetan border. The Lingshi Basin is one example, beginning with a foundation of marble and phyllite lying atop older crystalline rock, overlain by tillite and limestone. In the basin, migmatite gneiss is transgressed by calc-schist, breccia, quartzite, limestone and recrystallized fossils.