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