Chapter 6 Quiz
A pegmatite is a course-grained igneous rock that forms primarily because the melt
is water-rich.
Because of its physical properties, magma tends to
move upward, away from where it formed.
Viscosity does NOT depend on
the total volume of the magma body.
Igneous rocks are formed
through the freezing or crystallization of a melt.
If you find a tuff in the field, what type of geologic activity could you reasonably assume has occurred?
a volcanic eruption
Most commonly, felsic igneous rocks
are lighter in color than mafic rocks.
A vast, composite intrusive igneous body that covers hundreds of square kilometers (in a map view) is called a
batholith.
Differentiation of the Earth's iron core and collisions of planetesimals caused early Earth to
be much hotter than at present.
Volatiles refer to substances that
evaporate easily and exist as gases.
As compared to aphanitic igneous rocks, phaneritic rocks are
coarser grained.
The boundary formed between new intrusive igneous rock and the host rock around it is called a
contact.
A volcanic arc results from __________ tectonic movements and is associated with a __________.
convergent; subduction zone
As compared to coarse-grained igneous rocks, fine-grained igneous rocks
cool and solidify more quickly.
Intrusive rocks that form deep within the Earth ______________ than intrusive rocks that cool near the surface.
cool more slowly
If the volatile content of magma is increased, its viscosity will
decrease.
Vesicles in an igneous rock are evidence for which of the following?
degassing of volatiles
Which of the following is not typically associated with the eruption of a Large Igneous Province (LIP)?
emplacement of large granite batholiths
Which type of magma has the greatest silica content?
felsic
Large igneous provinces are formed by ________, which can flow tens to hundreds of kilometers.
flood basalts
As compared to mafic igneous rocks, felsic igneous rocks
have a higher proportion of silica relative to Mg oxide and Fe oxide.
If a body of magma becomes more felsic, its viscosity will
increase.
When magma solidifies below the surface of the Earth, ________ are formed.
intrusive igneous rocks
Which of the following processes is not responsible for the formation of magma within the Earth?
loss of volatiles to the atmosphere
A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock. These newly formed magmas are
mafic.
The difference between magma and lava is
magma is melt underground, whereas lava is melt that has emerged from the surface.
Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma melt?
melting due to heat transfer from rising magma
In general, when rock is partially melted, the chemistry of the melt is
more felsic than the original chemistry of the rock that was partially melted.
In general, if a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be
more felsic than the source rock.
During fractional crystallization of a magma body, the first rock that is expected to crystallize from the magma will be
more mafic than the magma.
The continuous series in Bowen's reaction series describes the crystallization behavior of which mineral?
olivine
In the discontinuous series of Bowen's reaction series, the first mineral to crystallize from a mafic melt is
olivine.
A _________ is an irregular or blob-shaped intrusive body; a ___________ is a blister-shaped intrusion.
pluton; laccolith
An igneous rock with a mixed texture consisting of coarse crystals (phenocrysts) surrounded by fine crystals (groundmass) is termed
porphyritic.
Pegmatites, which often occur in dikes, are unusual among shallow intrusive rocks in that they
possess exceptionally coarse grains.
A felsic, highly-vesicular volcanic rock is termed
pumice.
A fragmental, extrusive igneous rock is referred to as which of the following?
pyroclastic
Bombs, ash, and cinders are all examples of
pyroclastic debris.
Granite, an intrusive igneous rock, is most similar in mineral composition to which extrusive equivalent?
rhyolite
A magma body with a ________ volume and a ________ shape cools fastest.
smaller; pancake
Flood basalts such as those found in the Columbia Plateau and the Deccan region are associated with
superplumes.
Which of the following does not affect the cooling rate of magma?
tectonic setting
The geotherm is the rate of change of
temperature with depth in the Earth's interior.
Fragments of material erupted from a volcano eventually settle and lithify to form an extrusive igneous rock called
tuff.
Important volatiles in magmas include
water and carbon dioxide.