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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 ...
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]
Phyllite Banded gneiss with a dike of granite orthogneiss Marble Quartzite Manhattan Schist, from Southeastern New York Slate. Anthracite – Hard, compact variety of coal; Amphibolite – Metamorphic rock type; Blueschist – Type of metavolcanic rock; Cataclasite – Rock found at geological faults – A rock formed by faulting
Among English and American geologists the term is generally employed in this sense. [ 4 ] The granulites are very closely allied to the gneisses , as they consist of nearly the same minerals, but they are finer-grained, have usually less perfect foliation, are more frequently garnetiferous, and have some special features of microscopic structure.
High-grade metamorphism transforms the rock to gneiss, which is coarse to very coarse-grained. [37] Rocks that were subjected to uniform pressure from all sides, or those that lack minerals with distinctive growth habits, will not be foliated.
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 ...
Migmatite featuring felsic minerals, at Morton Gneiss Complex. Granitization is an old, and largely discounted, hypothesis that granite is formed in place through extreme metasomatism. The idea behind granitization was that fluids would supposedly bring in elements such as potassium, and remove others, such as calcium, to transform a ...
Location: the tectonic contact between the (autochthonous) Western Gneiss Region and rocks of the (allochthonous) Blåhø nappe on Otrøy, Caledonides, Central Norway. A mylonite (through a petrographic microscope) showing rotated so-called δ-clasts. The clasts show that the shear was dextral in this particular cut.