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Ultra-high-pressure metamorphism refers to metamorphic processes at pressures high enough to stabilize coesite, the high-pressure polymorph of SiO 2.It is important because the processes that form and exhume ultra-high-pressure (UHP) metamorphic rocks may strongly affect plate tectonics, the composition and evolution of Earth's crust.
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 plate tectonics rock cycle is an evolutionary process. Magma generation, both in the spreading ridge environment and within the wedge above a subduction zone, favors the eruption of the more silicic and volatile rich fraction of the crustal or upper mantle material. [ 9 ]
Tectonic phases can be extensional or compressional in nature. When numerous subsequent compressional tectonic phases share the same geodynamic cause (usually some plate tectonic mechanism) this is called an orogeny. During an orogeny tectonic phases lead to mountain building, which causes deformation and metamorphism of rocks.
These rocks are older than 570 million years and sometimes date back to around 2 to 3.5 billion years. [ citation needed ] They have been little affected by tectonic events following the end of the Precambrian, and are relatively flat regions where mountain building, faulting, and other tectonic processes are minor, compared with the activity ...
[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.
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 Streetcar to Subduction and Other Plate Tectonic Trips by Public Transport in San Francisco. doi:10.1029/SP022. ISBN 0-87590-234-0. Wakabayashi, John (1992). "Nappes, Tectonics of Oblique Plate Convergence, and Metamorphic Evolution Related to 140 Million Years of Continuous Subduction, Franciscan Complex, California". The Journal of Geology.