GEOL EXAM pt2ch6
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
igneous rocks are formed by
through the freezing or crystallization of a melt
Compare and contrast a dike and a sill. How do they relate to surrounding rock layers?
Dikes and sills are both tabular igneous intrusions. Dikes cut across preexisting layering (bedding or foliation), whereas sills intrude parallel to preexisting layering. Dikes are vertically oriented tabular intrusions, whereas sills are near horizontally oriented.
List the four major magma compositions in order of silica content. (highest -> lowest)
Felsic Intermediate Mafic Ultramafic
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 is called
batholith
differentiation of the earth's iron core and collisions of planetesimals caused early earth to
be much hotter than at present
As compared to aphanitic igneous rocks, phaneritic rocks are
coarser grained.
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
Vesicles in an igneous rock are evidence for which of the following?
degassing of volatiles
In the figure, what type of intrusion is the VERTICAL rock unit shown
dike
volatiles refers to substances that
evaporate easily and exist as gases
which type of magma has the greatest silica content
felsic
as compared to mafic igneous rocks, felsic igneous rocks
have a higher proportion of silica relative to Mg oxide and Fe oxide
Shiprock, New Mexico, is an
intrusion that represents the eroded remnant of an extinct volcano
when magma solidifies below the surface of the earth, are formed
intrusive igneous rocks
which of the following processes is not responsive for the formation of magma within the earth
loss of volatiles to the atmosphere
the difference between magma and lava is
magma is melt underground, whereas lava is melt that has emerged from the surface
in general, when rock is partially melted, the chemistry if 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
in the discontinuous series of Bowen's reaction series, the first mineral to crystallize from a mafic melt is
olivine
the continuous series in Bowen's Reaction series describes the crystallization of which mineral
plagioclase
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.
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
in the figure, what type of igneous intrusion is the HORIZONTAL rock unit shown
sill
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
Fragments of material erupted from a volcano eventually settle and lithify to form an extrusive igneous rock called
tuff
