Übung - Bowen's Reaction Series
(http://gomyclass.com/BowensReaction/index.html)
Bowen's Reaction Series demonstrated that as a basaltic magma cools, minerals tend to crystallize in
a systematic fashion based on their melting points. The first mineral to crystallize from a basaltic
magma is the ferromagnesian mineral olivine. Further cooling generates calcium- rich plagioclase
feldspar as well as pyroxene, and so forth down the diagram. Bowen's Reaction Series allows us to
interpret the cause and effect relationship between observed geologic features and their formative
geologic processes.
For questions 1-6, fill in the blanks in the paragraph below with the choices indicated.
Bowen's reaction series describes __1__ . The first minerals to crystallize are __2__ , hence the
residual melt will __3__ . If the early-formed minerals remain in contact with the melt, at lower
temperatures they will react with the silica in the melt to form new minerals. Reactions continue
until all of the silica in the melt is used-up or until biotite forms and the remaining melt crystallizes.
The resulting rock will have a __4__ . However, if the early formed minerals are separated from the
residual melt (e.g. crystal settling or "squeezing"), then they will not be able to react with the melt,
__5__occurs, and __6__ will be formed. The early-formed minerals will form a rock with a lower
concentration of silica than that of the parent magma, but the residual melt will eventually crystallize
to form a rock with a higher concentration of silica than that of the parent magma. Thus, rocks of
different compositions can be formed from the same parent magma.
1. Bowen's reaction series describes _____.
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where crystallization occurs
why some igneous rocks are aphanitic and others are phaneritic
the order in which minerals crystallize from a cooling magma
why silica tetrahedra bond in different ways
2. The first minerals to crystallize are ____.
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relatively poor in silica
3D-network silicates
fine-grained
relatively rich in silica
3. hence the residual melt will ____ ?
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be coarse-grained
be depleted in silica
be enriched in silica
crystallize to form single tetrahedron silicates
4. If the early-formed minerals remain in contact with the melt, at lower temperatures they will
react with the silica in the melt to form new minerals. Reactions continue until all of the silica in
the melt is used-up or until biotite forms and the remaining melt crystallizes. The resulting rock will
have a _______ .
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composition identical to the parent magma
much higher silica content than the original (parent) magma
extremely coarse grained (pegmatitic) texture
porphyritic texture
5. However, if the early formed minerals are separated from the residual melt (e.g. crystal settling
or "squeezing"), then they will not be able to react with the melt, ____occurs.
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Assimilation
magmatic differentiation
megadynamo-wizbanging
magma mixing
6. ... and _____ will be formed.
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rocks composed of carbonate mineral
porphyries
rocks with vesicular textures
rocks with different compositions
7. By examining Bowen's reaction series, we can see that olivine ______.
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is the most resistant to chemical weathering
crystallizes last
crystallizes first
does not crystalllize based on its melting point