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Geological map of the Hebridean terrane showing distribution of rocks of the Lewisian complex Undeformed Scourie dyke cutting Lewisian Gneiss, about 1.6 km west of Scourie Scourie dykes (now foliated amphibolites) cutting grey gneiss of the Scourie complex, both deformed during the Laxfordian tectonic event and cut by later (unfoliated) granite veins - road cutting on the A838 just north of ...
The non-metamorphic rocks fall into two classes: sedimentary rocks, formed from sediment, and igneous rocks, formed from magma. The source of the sediment of a sedimentary rock is termed its provenance. Magmatic protoliths can be further divided into three categories: ultramafic rock, mafic rock, and quartzo
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]
In some of the Blue Ridge Mountains occurrences, an epidotized augen gneiss is present exhibiting foliation structures. The dominant green epidote in unakite rocks is the metasomatic alteration product of plagioclase feldspar, while the orthoclase and quartz crystals remain unaffected.
The size of the aureole depends on the heat of the intrusion, its size, and the temperature difference with the wall rocks. Dikes generally have small aureoles with minimal metamorphism, extending not more than one or two dike thicknesses into the surrounding rock, [51] whereas the aureoles around batholiths can be up to several kilometers wide.
The oldest of these plutonic complexes, the Elves Chasm Gneiss, likely represents a small fragment of basement upon which the metavolcanic rocks that comprise the Granite Gorge Metamorphic Suite accumulated. The remainder of the Early Paleoproterozoic granites, granitic pegmatites, aplites, and granodiorites are parts of either younger plutons ...
The Narryer Gneiss terrane is a geological complex in Western Australia that is composed of a tectonically interleaved and polydeformed mixture of granite, mafic intrusions and metasedimentary rocks in excess of 3.3 billion years old, with the majority of the Narryer Gneiss terrane in excess of 3.6 billion years old.
Eoarchean geology is the study of the oldest preserved crustal fragments of Earth during the Eoarchean era from 4.031 to 3.6 billion years ago. Major well-preserved rock units dated to this era are known from three localities, the Isua Greenstone Belt in Southwest Greenland, the Acasta Gneiss in the Slave Craton in Canada, and the Nuvvuagittuq Greenstone Belt in the eastern coast of Hudson Bay ...