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Even though all magmas originate from similar mantle rocks, and also start the end as comparable magma, other things, favor partial melting and crystallization processes prefer magmatic differentiation, can change the chemistry of the magma. This describes the wide range of resulting igneous rocks that are discovered all over Earth.

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Partial Melting

Because the mantle is created of many different minerals, the does no melt uniformly. As minerals with lower melting point out turn into liquid magma, those with greater melting points remain as heavy crystals. This is recognized as partial melting. As magma gradually rises and cools into solid rock, it undergoes physical and also chemical alters in a procedure called magmatic differentiation.

According come Bowen’s Reaction collection (Section 4.2), each mineral has actually a distinctive melting and crystallization temperature. Since most rocks are made of numerous different minerals, as soon as they begin to melt, part minerals start melting sooner than others. This is recognized as partial melting and also creates magma through a various composition than the initial mantle material.

The most crucial example occurs as magma is produced from mantle rocks (as debated in section 4.3). The chemistry the mantle absent (peridotite) is ultramafic, short in silicates and also high in iron and also magnesium. When peridotite begins to melt, the silica-rich portions melt an initial due come their reduced melting point. If this continues, the magma becomes significantly silica-rich, transforming ultramafic mantle right into mafic magma, and also mafic mantle right into intermediate magma. The magma rises to the surface due to the fact that it is an ext buoyant than the mantle.

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During assimilation, pieces of country rock through a different, often more felsic, ingredient are added to the magma. This solid pieces may melt, which transforms the ingredient of the original magma. At times, the solid fragments may remain intact within the cooling magma and also only partly melt. The unmelted country rocks within an igneous rock mass are referred to as xenoliths.

Xenoliths are also common in the processes of magma mixing and rejuvenation, two various other processes the can contribute to magmatic differentiation. Magma mixing occurs when two different magmas come into contact and mix, despite at times, the magmas can remain heterogeneous and create xenoliths, dikes, and also other features. Magmatic rejuvenation happens as soon as a cooled and also crystallized body of absent is remelted and pieces that the initial rock may remain as xenoliths.

Much of the continental lithosphere is felsic (i.e. Granitic), and normally an ext buoyant than the underlying mafic/ultramafic mantle. As soon as mafic magma rises with thick continental crust, it does so slowly, more slowly than when magma rises with oceanic plates. This gives the magma several time to react with the surrounding nation rock. The mafic magma has tendency to assimilate felsic rock, becoming more silica-rich as it migrates through the lithosphere and transforming into intermediate or felsic magma by the time it will the surface. This is why felsic magmas space much much more common within continents.

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Figure \(\PageIndex1\): climbing magma diapirs in mantle and also crust. Fractional crystallization occurs in the diapirs in the crust. (Source: Woudloper)

Fractionation or fractional crystallization is another process that rises the magma silica content, making it more felsic <9>. As the temperature drops within a magma diapir rising through the crust, some minerals will certainly crystallize and settle to the bottom that the magma chamber, leaving the remaining melt depleted that those ions. Olivine is a mafic mineral in ~ the height of the Bowen’s Reaction series with a high melting allude and a smaller percent of silica matches other typical igneous minerals. Once ultramafic magma cools, the olivine crystallizes first and handle to the bottom of the magma room (see figure). This way the staying melt becomes much more silica-rich and also felsic. Together the mafic magma more cools, the following minerals on Bowen’s Reaction series (plagioclase and also pyroxene) crystallize next, remove even much more low-silica components from the magma, making the even an ext felsic. This crystal fractionation can occur in the oceanic lithosphere, yet the development of much more differentiated, highly progressed felsic magmas is largely confined come continental regions where the longer time come the surface allows much more fractionation come occur.