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.
How are gneiss and migmatite related?
The two rock types are certainly relatives, so to speak. If a gneiss experiences just slightly higher temperatures, it may partially melt and become a migmatite.
Is migmatite a high grade rock?
migmatite A coarse-grained, heterogeneous mixed rock consisting of: (a) a high-grade metamorphic component with a gneissose texture (see METAMORPHIC GRADE); and (b) an igneous component with a granite mineralogy and a foliated or unfoliated texture (see FOLIATION).
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.
What is a migmatite rock?
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 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 structure of migmatite gneiss near Vanduzi?
The structure of the migmatite gneiss near Vanduzi comprises layers of granitic leucosome with mafic selvedges (melanosome) at its margins (Fig. 6.1) suggesting that the melting system did not reach
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.
How many generations of migmatisation are there in gneiss?
Gneiss consists of more homogeneous biotite-quartz-feldspar gneiss with two generations of migmatisation recognisable in the field. The older leucosomes are recognised by their folded nature and are characterised by biotite-rich melanosomes whereas the younger melt patches are not
What is a migmatite vein?
Migmatites often appear as tightly, incoherently folded veins ( ptygmatic folds ). These form segregations of leucosome, light-colored granitic components exsolved within melanosome, a dark colored amphibole – and biotite -rich setting.