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زمینشناسی و معدن::
سنگهای پوسته ای
Typically, the silica content of crustal rocks ranges from a low of about 40 percent in ultramafic rocks to a high of morethan 70 percent in felsic rocks (see Figure 4.5).
Magma also can be generated when crustal rocks are heated sufficiently to melt.
Temperature Increase: Melting Crustal Rocks As soon as mantle-derived basaltic magma forms, it will buoyantly rise toward the surface.
In continental settings, basaltic magma often "ponds" beneath crustal rocks, which have a lower density and are already near their melting temperature.
The hot basaltic magma may heat the overlying crustal rocks sufficiently to generate a secondary, silica-rich magma.
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