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Fractional crystallization, or crystal fractionation, is one of the most important geochemical and physical processes operating within crust and mantle of a rocky planetary body, such as the Earth. It is important in the formation of igneous rocks because it is one of the main processes of magmatic differentiation . [ 1 ]
Assimilation can be broadly defined as a process where a mass of magma wholly or partially homogenizes with materials derived from the wall rock of the magma body. [1] Assimilation is a popular mechanism to partly explain the felsification of ultramafic and mafic magmas as they rise through the crust: a hot primitive melt intruding into a ...
During cooling, crystals will form from the melt. Thus, the crystal/melt ratio increases, generating a magma, a crystal-mush, and finally a cumulate rock. A crystal mush is magma that contains a significant amount of crystals (up to 50% of the volume) suspended in the liquid phase (melt). [1]
For instance, a magma of gabbroic composition can produce a residual melt of granitic composition if early formed crystals are separated from the magma. Gabbro may have a liquidus temperature near 1,200 °C, and the derivative granite-composition melt may have a liquidus temperature as low as about 700 °C.
More typically, they are mixes of melt and crystals, and sometimes also of gas bubbles. [15] Melt, crystals, and bubbles usually have different densities, and so they can separate as magmas evolve. [89] As magma cools, minerals typically crystallize from the melt at different temperatures. This resembles the original melting process in reverse.
At the bottom of the magma reservoir, a cumulate rock forms. Cumulate rocks are the typical product of precipitation of solid crystals from a fractionating magma chamber. These accumulations typically occur on the floor of the magma chamber, although they are possible on the roofs if anorthite plagioclase is able to float free of a denser mafic ...
[1], [3] The composition of silica within basaltic magma ranges from 45-55 weight percent (wt.%), or mass fraction of a species. [1] It forms in temperatures ranging from approximately 1830 °F to 2200 °F. [1], [3] Basaltic magma has the lowest viscosity and volatiles content, yet still may be up to 100,000 times more viscous than water. [1]
Rhyolite is an extrusive igneous rock, formed from magma rich in silica that is extruded from a volcanic vent to cool quickly on the surface rather than slowly in the subsurface. It is generally light in color due to its low content of mafic minerals, and it is typically very fine-grained ( aphanitic ) or glassy .