Where is new crust crystallization from magma

The minerals that make up igneous rocks crystallize solidify, freeze at a range of different temperatures. This explains why cooling magma can have some crystals within it and yet remain predominantly liquid. Norman Levi Bowen Figure 7. In he joined the Carnegie Institution in Washington, D. Working mostly with mafic magmas magmas rich in iron and magnesium , he determined the order of crystallization of minerals as the temperature drops.

First, he melted the rock completely in a specially made kiln. Then he allowed it to cool slowly to a specific temperature before quenching cooling it quickly so that no new minerals could form. The rocks that formed were studied under the microscope and analyzed chemically. This was done over and over, each time allowing the magma to cool to a lower temperature before quenching.

The result of these experiments was the reaction series which, even a century later, is still an important basis for our understanding of igneous rocks. This refers to the fact that one mineral is transformed into a different mineral through chemical reactions. On the right is the continuous series , where plagioclase feldspar goes from being rich in calcium to being rich in sodium. At about the point where pyroxene begins to crystallize, plagioclase feldspar also begins to crystallize.

At that temperature, the plagioclase is calcium-rich toward the anorthite end-member. As the temperature drops, and providing that there is sodium left in the magma, the plagioclase that forms is a more sodium-rich variety toward the albite end-member. The series is continuous because the mineral is always plagioclase feldspar, but the series involves a transition from calcium-rich to sodium-rich.

The proportions of the main chemical components of felsic, intermediate, and mafic magmas are listed in the table below. The values are similar to those shown in Figure 3. Chemical data for four rock samples are shown in the following table. Compare these with those in the table above to determine whether each of these samples is felsic, intermediate, or mafic. As a mafic magma starts to cool, some of the silica combines with iron and magnesium to make olivine.

As it cools further, much of the remaining silica goes into calcium-rich plagioclase, and any silica left may be used to convert some of the olivine to pyroxene. Soon after that, all of the magma is used up and no further changes takes place. The minerals present will be olivine, pyroxene, and calcium-rich plagioclase. If the magma cools slowly underground, the product will be gabbro ; if it cools quickly at the surface, the product will be basalt Figure 3.

As cooling continues, the various reactions on the discontinuous branch will proceed because silica is abundant, the plagioclase will become increasingly sodium-rich, and eventually potassium feldspar and quartz will form. Commonly even very felsic rocks will not have biotite or muscovite because they may not have enough aluminum or enough hydrogen to make the OH complexes that are necessary for mica minerals.

Typical felsic rocks are granite and rhyolite Figure 3. The cooling behaviour of intermediate magmas lie somewhere between those of mafic and felsic magmas. Typical intermediate rocks are diorite and andesite Figure 3. When ultramafic magma cools, the olivine crystallizes first and settles to the bottom of the magma chamber see figure. This means the remaining melt becomes more silica-rich and felsic.

This crystal fractionation can occur in the oceanic lithosphere, but the formation of more differentiated, highly evolved felsic magmas is largely confined to continental regions where the longer time to the surface allows more fractionation to occur. Reid, J. Magma mixing in granitic rocks of the central Sierra Nevada, California. Earth and Planetary Science Letters 66 , — Bateman, P. Geological Society of America Bulletin 90 , — Partial Melting Because the mantle is composed of many different minerals, it does not melt uniformly.

Crystallization and Magmatic Differentiation Liquid magma is less dense than the surrounding solid rock, so it rises through the mantle and crust. Fractional crystallization occurs in the diapirs in the crust. Source: Woudloper Fractionation or fractional crystallization is another process that increases the magma silica content, making it more felsic [ 9 ].

This means that minerals are separated out from the magma as it cools. However, these minerals contain only minor amounts of the trace elements. As a result, trace elements build up in the magma over time, as the magma chamber is continually replenished by new magma coming in to the system. Materials provided by Carnegie Institution. Note: Content may be edited for style and length.

Science News. Their work is published in Nature on November Story Source: Materials provided by Carnegie Institution.