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formed minerals can be separated from the melt, thus halting any further chemical
reaction. Minerals crystallize from a magma of basaltic composition under laboratory
conditions. Evidence that this highly idealized crystallization model approximates what
can happen in nature comes from the analysis of igneous rocks. In particular, we find
that minerals that form in the same general temperature regime depicted on Bowen’s
reaction series are found together in the same igneous rocks.
Bowen demonstrated that minerals crystallize from magma in a systematic
fashion. But how do Bowen’s findings account for the great diversity of igneous rocks?
It has been shown that, at one or more stages during the crystallization of magma, a
separation of various components can occur. One mechanism that allows this to happen
is called crystal settling. This process occurs when the earlier-formed minerals are more
dense (heavier) than the liquid portion and sink toward the bottom of the magma
chamber. When the remaining melt solidifies—either in place or in another location if it
migrates into fractures in the surrounding rocks—it will form a rock with a mineralogy
much different from the parent magma. The formation of one or more secondary
magmas from a single parent magma is called magmatic differentiation.

Task 3. Look at Figure 4.2. Bowen’s reaction series shows the sequence in
which minerals crystallize from a magma. Which is the first mineral to crystallize?
Which minerals generate cooling further according to the diagram?

Task 4. Discuss the following questions:
1. N. L. Bowen’s investigation.
2. Bowen’s reaction series.
3. Magmatic differentiation.

Individual work

Task 1. Read the text and translate it into Ukrainian (in written form).
Build up a list of key terms to the text.

Assimilation and Magma Mixing
Once a magma body forms its composition can also change through the
incorporation of foreign material. For example, as magma migrates through the crust, it
may incorporate some of the surrounding host rock, a process called assimilation. In a
near surface environment where rocks are brittle, magma causes numerous cracks in the
overlying rock as it pushes upward. The force of the injected magma is often sufficient
to dislodge blocks of “foreign” rock, which melt and are incorporated into the magma
body.
Another means by which the composition of magma can be altered is magma
mixing. This process occurs when one magma body intrudes another that has a different
composition. Once combined, convective flow may stir the two magmas and generate a
mass having a composition that is a blend of the two. Magma mixing may occur during
the ascent of two chemically distinct magma bodies as the more buoyant mass overtakes
the more slowly moving mass.
In summary, Bowen successfully demonstrated that through magmatic
differentiation, a single parent magma can generate several mineralogically different
igneous rocks.

Partial Melting and Magma Composition
The crystallization of basaltic magma occurs over a temperature range of at least
200°C. Melting, the reverse process spans a similar temperature range. As rock begins

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