How do you identify a migmatite?
Mafic minerals are generally darker in color, often black, brown, or dark green. Migmatites actually look very similar to a related rock: gneiss. Gneisses also contain alternating light and dark layers which result under high-pressure and high-temperature conditions.
What is migmatite gneiss?
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.
Which type of fold is associated with migmatite?
Migmatite textures Ptygmatic folds are formed by highly plastic ductile deformation of the gneissic banding, and thus have little or no relationship to a defined foliation, unlike most regular folds.
What is the texture of migmatite?
Migmatite – a high grade Barrovian metamorphic rock that has begin to fractionally melt. In appearance it looks like a gneiss intermixed with patches and splotches of phaneritic (coarse grained) igneous texture.
Which metamorphic facies does migmatite typically form?
granulite facies, one of the major divisions of the mineral facies classification of metamorphic rocks, the rocks of which formed under the most intense temperature-pressure conditions usually found in regional metamorphism. At the upper limit of the facies, migmatite formation may occur.
What kind of rock is migmatite?
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.
Why a migmatite is both an igneous and metamorphic rock?
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.
Where should migmatite be placed in the rock cycle?
Migmatite is a rock that straddles the fence separating metamorphic and igneous. Like the example we saw yesterday, it’s a rock on the cusp of one of the major transitions in the rock cycle.
Is migmatite an igneous rock?
What kind of monazite is in a migmatite?
Granulite facies migmatites (750 – 900°C, 5 – 6 kbar) from the Namaqualand Metamorphic Complex, South Africa, contain complex zoned monazite in both palaeosome and neosome domains.
What is the heterogeneous nature of a migmatite?
The heterogeneous nature of migmatites at various scales represents the final product of petrological and mechanical processes that create and redistribute anatectic melt with or without accompanying deformation.
What kind of rocks are migmatites made of?
Migmatites are hybrid rocks: the dark layers (most often composed of biotite and amphibole) experienced metamorphic changes, but did not melt.
What is the geochronology of a migmatite?
Geochronology of accessory and major minerals in migmatites can determine the timing and duration of melting. Migmatites may host mineral deposits and open-system processes associated with partial melting may enrich or deplete elements of economic interest.