Bowen’s idea of fractional crystallization of basaltic magma as a means of producing the broad variety of igneous rocks, while certainly a natural and laboratory process, does not completely answer the big picture. Why not?
Answer to relevant QuestionsWhat are some other theories which explain why there are different kinds of magma?If a magma crystallizes at a temperature of about 1500°C, what is its likely composition— felsic or mafic? (See Fig. 3.3.)A layer of granite 1 m thick is present in a sequence of sedimentary rocks, parallel to the bedding in the sedimentary rocks (Fig. 3.8). Is it a dike, a sill, or a stock?What is the fine-grained equivalent of gabbro?Note the similarities in the sketches of Mt. St. Helens (Fig. 3.11) and Crater Lake, Oregon (Fig. 3.12). Surmise how Crater Lake may have formed.
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