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Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock ( protolith ) is subjected to temperatures greater than 150 to 200 °C (300 to 400 °F) and, often, elevated pressure of 100 megapascals (1,000 bar ) or more, causing profound physical or chemical changes.
The third form of rock material found on Earth is metamorphic rock, which is created from the transformation of pre-existing rock types through high pressures, high temperatures, or both. The most abundant silicate minerals on the Earth's surface include quartz , the feldspars , amphibole , mica , pyroxene , and olivine . [ 25 ]
The rocks must be brittle and fracture to create the planes along which the magma intrudes the parent rock bodies, whether this occurs along preexisting planes between sedimentary or volcanic beds or weakened planes related to foliation in metamorphic rock. These planes or weakened areas allow the intrusion of a thin sheet-like body of magma ...
L-Tectonites are aligned in a linear fabric, which allows the rock to split into rod-like shapes due to the two intersecting planes. The foliation of this type is not strong. S-Tectonites are the fabric that is dominantly a foliation fabric which allows the rock to split into plate-like sheets that are parallel to foliation.
A shield is a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. [1] These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years.
Metamorphic rocks with clockwise P-T-t paths are commonly associated with a near-isothermal decompressional P-T trajectory. [5] [6] Clockwise P-T-t path normally consists of three parts: [2] Initial heating and compression until arriving a peak, a high pressure-low temperature peak is often observed. (Prograde metamorphism until peak) [2]
[33] [34] Subsequent erosion of the mountains exposes the roots of the orogenic belt as extensive outcrops of metamorphic rock, [35] characteristic of mountain chains. [33] Metamorphic rock formed in these settings tends to shown well-developed foliation. [33] Foliation develops when a rock is being shortened along one axis during metamorphism.
High δ 18 O values of zircons represent rock recycled at the Earth's surface and thus potentially producing mixed samples. [24] The outcome of this combined analysis is valid zircons showing periods of increased crustal generation at 1.9 and 3.3 Ga, the latter of which representing the time period following the commencement of global plate ...