Granitoids are a everywhere element of the crust. They have crystallized from magmas that have composition at a eutectic point. Magmas will evolve to the eutectic because of igneous division, or because they represent low degrees of partial melting. Fractional crystallisation serves to reduce a melt in iron, magnesium, titanium, calcium and sodium, and enrich the melt in potassium and silicon - alkali feldspar and quartz (SiO2), are two of the important constituents of granite.
This process operates regardless of the origin of the parental molten rock to the granite, and anyway of its chemistry. However, the composition and origin of the magma which differentiate into granite, leaves certain geochemical and mineralogical evidence as to what the granite's parental rock was. The final mineralogy, texture and chemical work of a granite is often distinctive as to its origin. For occurrence, a granite which is formed from melted sediments may have more alkali feldspar, whereas a granite derived from melted basalt may be richer in plagioclase feldspar.
This process operates regardless of the origin of the parental molten rock to the granite, and anyway of its chemistry. However, the composition and origin of the magma which differentiate into granite, leaves certain geochemical and mineralogical evidence as to what the granite's parental rock was. The final mineralogy, texture and chemical work of a granite is often distinctive as to its origin. For occurrence, a granite which is formed from melted sediments may have more alkali feldspar, whereas a granite derived from melted basalt may be richer in plagioclase feldspar.
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