api/deki/files/5084/girl-160172__340.png?origin=mt-web" title="Chris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & cam Mosher" />Contributed by kris Johnson, Matthew D. Affolter, Paul Inkenbrandt, & camer Mosher

Even though every magmas originate from similar mantle rocks, and also start out as comparable magma, various other things, like partial melting and crystallization processes prefer magmatic differentiation, can adjust the chemistry the the magma. This defines the wide selection of result igneous rocks that are discovered all over Earth.

You are watching: Contrast partial melting and fractional crystallization


Partial Melting

Because the mantle is written of many different minerals, the does not melt uniformly. As minerals with lower melting points turn right into liquid magma, those with higher melting points remain as heavy crystals. This is recognized as partial melting. As magma gradually rises and cools right into solid rock, it undergoes physical and chemical transforms in a process called magmatic differentiation.

According come Bowen’s Reaction collection (Section 4.2), each mineral has actually a distinct melting and crystallization temperature. Because most rocks room made of many different minerals, once they begin to melt, some minerals start melting sooner 보다 others. This is well-known as partial melting and also creates magma with a various composition than the initial mantle material.

The most vital example occurs as magma is generated from mantle rocks (as disputed in section 4.3). The chemistry that mantle absent (peridotite) is ultramafic, short in silicates and also high in iron and also magnesium. As soon as peridotite starts to melt, the silica-rich parts melt first due to their reduced melting point. If this continues, the magma becomes progressively silica-rich, transforming ultramafic mantle right into mafic magma, and also mafic mantle right into intermediate magma. The magma rises come the surface because it is more buoyant than the mantle.

*
api/deki/files/8240/04.16_Xenoliths_Little_Cottonwood_Canyon-300x211.jpg?revision=1&size=bestfit&width=341&height=240" />Figure (PageIndex1): Xenoliths in tiny Cottonwood Stock, Utah

During assimilation, piece of nation rock through a different, often much more felsic, composition are included to the magma. This solid pieces may melt, which transforms the composition of the initial magma. In ~ times, the solid pieces may remain undamaged within the cooling magma and also only partly melt. The unmelted nation rocks in ~ an igneous rock mass are dubbed xenoliths.

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

Much the the continental lithosphere is felsic (i.e. Granitic), and also normally much more buoyant 보다 the basic mafic/ultramafic mantle. As soon as mafic magma rises v thick continental crust, the does so slowly, much more slowly than once magma rises with oceanic plates. This provides the magma lots of time to react through the surrounding country rock. The mafic magma often tends to assimilate felsic rock, becoming much more silica-rich together it migrates through the lithosphere and an altering into intermediate or felsic magma by the moment it get the surface. This is why felsic magmas room much an ext common in ~ continents.

See more: Driving Distance From Columbia Sc To Myrtle Beach Sc To Myrtle Beach, Sc

*
Figure (PageIndex1): increasing magma diapirs in mantle and crust. Fractional crystallization wake up in the diapirs in the crust. (Source: Woudloper)

Fractionation or fractional crystallization is another process that boosts the magma silica content, make it an ext felsic <9>. Together the temperature drops within a magma diapir climbing through the crust, some minerals will certainly crystallize and also settle come the bottom that the magma chamber, leaving the continuing to be melt depleted that those ions. Olivine is a mafic mineral at the top of the Bowen’s Reaction series with a high melting allude and a smaller portion of silica matches other usual igneous minerals. When ultramafic magma cools, the olivine crystallizes first and handle to the bottom of the magma chamber (see figure). This means the remaining melt becomes more silica-rich and felsic. As the mafic magma additional cools, the next minerals ~ above Bowen’s Reaction collection (plagioclase and also pyroxene) crystallize next, removed even more low-silica contents from the magma, making the even more felsic. This decision fractionation can happen in the oceanic lithosphere, yet the development of much more differentiated, highly advanced felsic magmas is mainly confined come continental areas where the much longer time to the surface ar allows more fractionation to occur.