How do you identify a migmatite?
migmatite, in geology, rock composed of a metamorphic (altered) host material that is streaked or veined with granite rock; the name means “mixed rock.” Such rocks are usually gneissic (banded) and felsic rather than mafic in composition; they may occur on a regional scale in areas of high-grade metamorphism.
What is a migmatite in geology?
A migmatite is a metamorphic rock formed by anatexis that is generally heterogeneous and preserves evidence of partial melting at the microscopic to macroscopic scale. Migmatites represent the transition from metamorphic to igneous rocks in the rock cycle.
What is the difference between migmatite and gneiss?
is that gneiss is (geology) a common and widely-distributed metamorphic rock having bands or veins, but not schistose while migmatite is (geology) any rock of mixed appearance, being an intimate mixture of granite and older rock, specifically from intense metamorphism which partially melts the rock, causing it to …
How migmatite is formed?
Migmatites form under extreme temperature and pressure conditions during prograde metamorphism, when partial melting occurs in metamorphic paleosome. Components exsolved by partial melting are called neosome (meaning ‘new body’), which may or may not be heterogeneous at the microscopic to macroscopic scale.
Which metamorphic facies does migmatite typically form?
What is migmatite used for?
Migmatites have an attractive appearance, often being marked with irregular small stripes or patches of contrasting shades ranging from almost white to dark grey, and are widely used as building stone, sometimes being polished for ornament.
Why is migmatite igneous and metamorphic?
Granites are igneous rocks that form from magma, which is melted rock. Migmatite rock lies at the interface between metamorphic and igneous rock. What I mean by this is that migmatites are metamorphic rocks formed via melting of rock — but melted rock is magma — and igneous rock comes from magma.
What is the difference between Blueschist and greenschist facies?
As nouns the difference between blueschist and greenschist is that blueschist is (geology) a metamorphic rock containing glaucophane while greenschist is a metamorphic rock formed at low temperature and pressure, often with an abundance of green minerals such as chlorite, serpentine, and epidote.
Does migmatite form along faults?
A migmatite is a dynamic metamorphic rock that typically forms along faults.
Is eclogite a metamorphic facies?
It is a rock type that gave name to a metamorphic facies. Eclogite facies is characterized by pressures in excess of 1.2 GPa (45 km depth) and temperature exceeding at least 400-500 °C. 400-500 degrees at 45 km depth is below the crustal average (25 °C per kilometer of depth).
Where is eclogite facies found?
connection with eclogite facies A classic area of occurrence is western California.
How are migmatites formed?
Commonly, migmatites occur below deformed metamorphic rocks that represent the base of eroded mountain chains, commonly within Precambrian cratonic blocks, Migmatites form under extreme temperature and pressure conditions during prograde metamorphism, when partial melting occurs in metamorphic paleosome.
What is a metamorphic migmatite?
Migmatites are hybrid rocks: the dark layers (most often composed of biotite and amphibole) experienced metamorphic changes, but did not melt.
What is the evidence for the existence of migmatites?
The presence of migmatites was one line of evidence that geologists examined to determine that granites probably formed through melting processes, not through chemical alteration processes.
How does a gneiss turn into a migmatite?
If a gneiss experiences just slightly higher temperatures, it may partially melt and become a migmatite. Most migmatites probably were gneisses on their way to becoming true hybrid metamorphic-igneous (metagneous? ignamorphic?) rocks.