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Metamorphism is further divided into prograde and retrograde metamorphism. Prograde metamorphism involves the change of mineral assemblages (paragenesis) with increasing temperature and (usually) pressure conditions. These are solid state dehydration reactions, and involve the loss of volatiles such as water or carbon dioxide.
A typical clockwise P-T-t path representing a collision or subduction setting. Prograde metamorphism occurred upon increasing P-T environment until reaching the peak, followed by near-isothermal decompression (Stage 1 retrograde metamorphism), and further exhumation and erosion (Stage 2 retrograde metamorphism).
Prograde can refer to: Retrograde and prograde motion, in astronomy, a type of motion of astronomical bodies; Metamorphism#Prograde and retrograde, in geology, describes mineral changes in rocks under increasing pressure and/or temperature conditions; Progradation, in geography / geomorphology, refers to the growth of a river delta
A retrograde black hole – one whose spin is opposite to that of its disk – spews jets much more powerful than those of a prograde black hole, which may have no jet at all. Scientists have produced a theoretical framework for the formation and evolution of retrograde black holes based on the gap between the inner edge of an accretion disk ...
The growth of platy minerals, typically of the mica group, is usually a result of prograde metamorphic reactions during deformation. Often, retrograde metamorphism will not form a foliation because the unroofing of a metamorphic belt is not accompanied by significant compressive stress.
This contact metamorphism results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma that add chemicals to the surrounding rock (metasomatism). Any pre-existing type of rock can be modified by the processes of metamorphism. [4] [5]
A metamorphic facies is a set of mineral assemblages in metamorphic rocks formed under similar pressures and temperatures. [1] The assemblage is typical of what is formed in conditions corresponding to an area on the two dimensional graph of temperature vs. pressure (See diagram in Figure 1). [1]
Mineral alteration refers to the various natural processes that alter a mineral's chemical composition or crystallography. [1]Mineral alteration is essentially governed by the laws of thermodynamics related to energy conservation, relevant to environmental conditions, often in presence of catalysts, the most common and influential being water (H 2 O).