geol 101: 2.4
Despite the fact that the temperatures within Earth are hot enough to melt rock, Earth is mostly solid. Why do the rocks within Earth NOT melt? A. The pressure is too high. B. The pressure is too low. C. There is not enough water. D. They are not in contact with air.
A. The pressure is too high.
Which type of plate boundary hosts the most explosive volcanoes? A. convergent only B. divergent only C. transform and convergent D. convergent and divergent
A. convergent only
As compared to coarse-grained igneous rocks, fine-grained igneous rocks ________. A. cool and solidify more quickly B. cool and solidify more slowly C. solidify at higher temperatures D. solidify at lower temperatures
A. cool and solidify more quickly
Which type of magma has the greatest silica content? A. felsic B. intermediate C. mafic D. ultramafic
A. felsic
All other factors being equal, if a body of magma becomes more felsic, its viscosity will ________. A. increase B. decrease C. stay the same D. Chemical composition has no effect on viscosity.
A. increase
An oceanic plate subducting under another oceanic plate will create a(n) ________. A. island arc B. continental arc C. continental rift D. transform fault
A. island arc
Decompression melting occurs at both ________ and ________. A. mid-ocean ridges; hotspots B. mid-ocean ridges; trenches C. subduction zones; hotspots D. subduction zones; mid-ocean ridges
A. mid-ocean ridges; hotspots
Magma tends to ________. A. move upward, away from where it formed B. move downward, away from where it formed C. move laterally D. stay in one place
A. move upward, away from where it formed
In Bowen's discontinuous reaction series, the first mineral to crystallize from a mafic melt is ________. A. olivine B. plagioclase C. pyroxene D. quartz
A. olivine
Stoping by magmas occurs when ________. A. pieces of surrounding country rock are broken off and assimilated B. the magma stops flowing and starts to solidify C. the magma becomes fully solidified to form intrusive rock D. the magma alters a thin rind of surrounding country rock
A. pieces of surrounding country rock are broken off and assimilated
Volcanic eruptions at divergent boundaries generally take the form of ________. A. pillow basalts B. pyroclastic flows C. lava domes D. pyroclastic falls
A. pillow basalts
An igneous rock with a mixed texture of coarse crystals (phenocrysts) surrounded by fine crystals (groundmass) is termed ________. A. porphyritic B. phaneritic C. aphanitic D. necrotic
A. porphyritic
The composition of magma will ________ when it erupts and turns into lava. A. remain the same B. become more felsic C. become more mafic D. have more silica
A. remain the same
The mantle is composed entirely of ________. A. solid peridotite B. solid basalt C. molten peridotite D. molten basalt
A. solid peridotite
A sill is a(n) ________. A. tabular intrusion that lies parallel to surrounding layers of sedimentary rock B. cooled layer of an ancient lava flow C. intrusion formed within the magma chamber of a volcano D. tabular intrusion that cuts across preexisting layers
A. tabular intrusion that lies parallel to surrounding layers of sedimentary rock
Most commonly, felsic igneous rocks ________. A. contain more iron and magnesium than intermediate rocks B. are lighter in color than mafic rocks C. are darker in color than mafic rocks D. are found in oceanic crust
B. are lighter in color than mafic rocks
The presence of vesicles in an igneous rock is evidence that the source melt ________. A. had a mafic composition B. contained dissolved volatiles C. underwent fractional crystallization D. was stoping and assimilating wall rock
B. contained dissolved volatiles
If the volatile content of magma is increased, its viscosity will ________. A. increase B. decrease C. stay the same D. Volatile content has no effect on viscosity.
B. decrease
All other factors being equal (i.e., depth, volume, temperature, etc.), which type of igneous intrusion would cool fastest? A. pluton B. dike C. batholith D. All intrusions cool at the same rate.
B. dike
Volcanoes whose magma source is NOT linked to a plate boundary are associated with ________. A. continental rifts B. hot spots C. mid-ocean ridges D. subduction zones
B. hot spots
If a body of magma is subjected to fractional crystallization, the first rock that is expected to crystallize from the magma will be ________. A. identical in chemical composition to the magma B. more mafic than the magma C. more felsic than the magma D. The composition of the rock is not predictable.
B. more mafic than the magma
An irregular-shaped and blob-like igneous rock body that cooled beneath the surface of Earth is a ________. A. dike B. pluton C. sill D. laccolith
B. pluton
The extremely high ________ within Earth keeps the rocks solid. A. temperature B. pressure C. silica content D. water content
B. pressure
IMAGE In the figure provided below, what type of igneous intrusion is the horizontal rock unit shown by letter A? A. dike B. sill C. pluton D. laccolith
B. sill
IMAGE Given the solidus and liquidus curves below, which location represents material that is partially melted? A B C D
C
________ melting occurs at subduction zones because the down-going plate ________. A. Heat transfer; is extremely hot B. Heat transfer; creates abundant friction C. Flux; contains abundant water D. Decompression; rises toward the surface
C. Flux; contains abundant water
Volcanic arcs form along ________ boundaries. A. transform B. transvergent C. convergent D. divergent
C. convergent
IMAGE The image below is of a ________. A. sill B. pluton C. dike D. batholith
C. dike
The formation of a hotspot is thought to be associated with ________. A. convergent boundaries B. divergent boundaries C. mantle plumes D. mid-ocean ridges
C. mantle plumes
Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma melt? A. melting due to a decrease in pressure B. melting due to an addition of volatiles C. melting due to heat transfer from rising magma D. melting due to an increase in pressure
C. melting due to heat transfer from rising magma
In general, if a body of igneous (source) rock is subjected to partial melting, the magma that is produced is expected to be ________. A. identical in chemical composition to the source rock B. more mafic than the source rock C. more felsic than the source rock D. The melt composition is not predictable.
C. more felsic than the source rock
Important volatiles in magmas include ________. A. mafic minerals, such as olivine B. potassium and aluminum C. water and carbon dioxide D. silicon and iron
C. water and carbon dioxide
Which of the following pictures of volcanoes is not the result of a convergent boundary? A. B. C. D.
D
IMAGE Which of the following is NOT a characteristic of the extrusive igneous rock obsidian? A. It is composed of volcanic glass. B. It possesses conchoidal fracture. C. It is typically felsic in composition. D. It likely cooled very slowly.
D. It likely cooled very slowly.
Viscosity controls how ________. A. hot the fluid is B. fast a rock will melt C. quickly the fluid cools D. fast a fluid flows
D. fast a fluid flows
The formation of magma within Earth is NOT caused by which of the following processes? A. decompression (drop in pressure) B. addition of volatiles C. transfer of heat from adjacent magma or very hot rocks D. loss of volatiles to the atmosphere
D. loss of volatiles to the atmosphere
Ash, and larger fragments of pumice are all examples of ________. A. intrusive igneous rocks B. hot spots C. volatiles D. pyroclastic debris
D. pyroclastic debris
Coarse-grained granite is most similar in mineral composition to fine-grained ________. A. andesite B. basalt C. gabbro D. rhyolite
D. rhyolite
Viscosity does NOT depend on ________. A. temperature B. volatile content C. silica content D. volume of the magma
D. volume of the magma
As compared to mafic igneous rocks, all felsic igneous rocks ________. cool and solidify more quickly cool and solidify more slowly solidify at higher temperatures solidify at lower temperatures
solidify at lower temperatures
