Geology Chapter 4

Which of the following statements is FALSE? Volcanic arcs A. form where subduction takes place. B. are long, curving mountain chains adjacent to deep-ocean trenches. C. can be continental or island-related. D. occur at divergent plate boundaries.

D. occur at divergent plate boundaries.

"Wet" igneous rock melts at a lower temperature than the "dry" version of that same rock because A. the addition of volatiles in "wet" rocks lowers their melting temperature. B. they occur on the seafloor, where temperatures are already cold. C. "dry" igneous rocks are made of more felsic minerals. D. "wet" igneous rocks form at shallower depth in the Earth.

A. the addition of volatiles in "wet" rocks lowers their melting temperature.

The following four figures show several different tectonic settings where volcanism is active. Which of the following images shows a tectonic environment where magmas were produced by flux-melting? A B C D

B

What are vesicles? A. pieces of wall rock broken off by intruding magma B.large crystals floating in a fine-grained groundmass C. air pockets or bubbles frozen in igneous rocks as gas escaped during cooling D. horizontal igneous intrusions

C. air pockets or bubbles frozen in igneous rocks as gas escaped during cooling

Pillow basalts A. occur in tabular intrusions called dikes. B. are composed of felsic lava. C. are formed in a submarine environment. D. contain large crystals that cool slowly.

C. are formed in a submarine environment.

Which is NOT a tectonic setting for igneous activity? A. hot spots B. continental rifts C. continental transform fault zones D. volcanic arcs bordering ocean trenches

C. continental transform fault zones

Identify the FALSE statement. Early Earth had numerous heat sources for igneous activity, including A. conversion of the kinetic energy of meteorite impact to heat energy. B. conversion of the kinetic energy of iron alloy sinking toward Earth's center to heat energy. C. decay of all of its radioactive elements; almost none remain today. D. the compression of mass into a smaller volume.

C. decay of all of its radioactive elements; almost none remain today.

Igneous rocks are formed by cooling magma or lava. Whether the rock cools intrusively or extrusively has a profound impact on a rock's texture. Which statement BEST describes the texture and depositional environment of the rocks shown in the figure? A. glassy to fine-grained from cooling intrusively B. coarse-grained from cooling intrusively C. glassy to fine-grained from cooling extrusively D. coarse-grained from cooling extrusively

C. glassy to fine-grained from cooling extrusively

Identify the FALSE statement. Magma moves upward toward the Earth's surface A. because it is less dense than the surrounding rock. B. slowly, working its way up through cracks and narrow conduits. C. more quickly as it cools and therefore becomes less viscous. D. because the weight of overlying rock creates pressure that squeezes it up.

C. more quickly as it cools and therefore becomes less viscous.

Identify the FALSE statement. Large igneous provinces (LIPs) A. are places where huge amounts of mafic magma have been erupted or intruded. B. represent special events in Earth's history that may have been caused by superplume activity. C. occur only along continental margins. D. may have profound impacts on the environment, including land, ocean, and atmospheric processes.

C. occur only along continental margins.

Which of the following is NOT an intrusive igneous structure? A. batholith B. laccolith C. pillow lava D. sill

C. pillow lava

The following image shows samples, both in hand sample and in microscope thin-section views. The textures are the result of their emplacement mechanism (intrusive, extrusive, or pyroclastic). Match the texture term with the appropriate picture set. A.) A - Crystalline, B - Glassy, C - Fragmental B.) A - Glassy, B - Fragmental, C - Crystalline C.) A- Crystalline, B - Fragmental, C - Glassy D.) A - Fragmental, B - Glassy, C - Crystalline

C.) A- Crystalline, B - Fragmental, C - Glassy

How does subduction trigger melting? A. Flux melting of the asthenosphere above the subducting slab creates a rising melt. B. The downgoing slab melts as it reaches hotter temperatures deep in the Earth. C. The overriding slab insulates the subducting slab, increasing temperature and causing melting. D. The subducting slab is made of felsic minerals, and therefore melts at lower temperatures.

A. Flux melting of the asthenosphere above the subducting slab creates a rising melt.

A black, fine-grained tabular intrusion between two layers of horizontal sedimentary rock must logically be a A. basaltic sill. B. granitic sill. C. basaltic dike. D. granitic dike.

A. basaltic sill.

Identify the FALSE statement. Pegmatites A. have intruded at great depth and cooled very slowly. B. can contain crystals up to tens of centimeters across. C. occur in tabular intrusions called pegmatite dikes. D. are an igneous rock type, distinguished by their unusual grain size.

A. have intruded at great depth and cooled very slowly.

The dramatic scenery of the Sierra Nevada in California, shown here A. owes its existence to erosion of a batholith. B. is the result of a continental hot spot. C. is especially impressive because of its dark-colored basalt rock. D. is composed of fine-grained volcanic rock.

A. owes its existence to erosion of a batholith.

Certain minerals are commonly found together in different igneous rocks. According to the following figure, which two minerals are you unlikely to find forming in the same rock? A. quartz and olivine B. pyroxene and amphibole C. amphibole and k-feldspar D. k-feldspar and plagioclase

A. quartz and olivine

An igneous rock has a medium-gray, fine-grained groundmass with large crystals of plagioclase. Which of the following statements about it is FALSE? A. It could logically be porphyritic andesite. B. The lava flow that produced it got quenched in ocean water. C. The plagioclase crystals are called phenocrysts. D. It began to crystallize at depth from intermediate-composition magma, then rose to the surface and became a lava flow.

B. The lava flow that produced it got quenched in ocean water.

Refer to the figure below. Which of the following statements is TRUE as a sample changes from point A to point B on the diagram? A. The sample heats up. B. The sample begins to melt due to decompression. C. The sample stays at the same depth within the Earth. D. The sample does not change its physical state because its temperature has not changed.

B. The sample begins to melt due to decompression.

Bowen's reaction series A. shows that minerals crystallize in a random order, with no particular pattern involved. B. allows a geologist to predict what minerals will be found in a given igneous rock. C. is an attempt to explain the logic of formation of sedimentary rocks. D. explains why some compounds use ionic bonds and others have covalent bonding.

B. allows a geologist to predict what minerals will be found in a given igneous rock.

Granite A. is an extrusive igneous rock. B. is felsic in composition. C. logically could be found in a lava flow. D. is the coarse-grained equivalent of andesite.

B. is felsic in composition

After an explosive volcanic eruption on an island, the surrounding sea is full of light-gray floating rock. What must it be? A. rhyolite B. pumice C. obsidian D. basalt

B. pumice

The texture of an igneous rock is dependent on its emplacement mechanism (how and where the lava or magma cooled). Match the following images with their emplacement mechanism; A.) A - Intrusive, B - Extrusive, C - Pyroclastic B.) A - Intrusive, B - Pyroclastic, C - Extrusive C.) A - Pyroclastic, B - Extrusive, C - Intrusive D.) A - Extrusive, B - Pyroclastic, C - Intrusive

B.) A - Intrusive, B - Pyroclastic, C - Extrusive

This is a picture of a basaltic lava flow. Choose the letter on the image that BEST approximates how a rock like this would form. A B C D

C

Interpret this diagram to find the FALSE statement. Point A represents rock that fits the following description. A. Its temperature is about 1700°C. B. It is mantle rock. C. It is under about 100,000 bar (100 kbar) of pressure. D. Its physical state is molten.

D. Its physical state is molten.

Viscosity is a material's resistance to flow. The pictures below show two types of volcanic eruptions. In the first, lava is fountaining and flowing freely, making a gently sloping volcano. In the second eruption, a thick plug of lava called a dome has emerged in a volcanic crater. Which of the following statements BEST describes the relative viscosity of these two eruptions? A. The lava dome (2) is lower viscosity than the fountaining lava (1). B. The two lavas have similar viscosities. C. Nothing about relative viscosity can be determined from the images. D. The lava dome (2) is higher viscosity than the fountaining lava (1).

D. The lava dome (2) is higher viscosity than the fountaining lava (1).

Which of the following statements is FALSE? Igneous rocks A. form from the cooling and crystallization of either lava or magma. B. form in great quantity along the mid-ocean ridge. C. are abundant, making up the entire ocean crust and much of continental crust. D. are coarse-grained if they cool extrusively.

D. are coarse-grained if they cool extrusively.

Magmas have a variety of chemical compositions because of all of the following EXCEPT A. they come from a variety of source rocks. B. the rocks that melt to make magma are composed of many minerals, not all of which melt under the same conditions. C. the magmas' heat can melt rock from the walls of the magma chamber. D. different magmas formed in different locations are isolated and don't mix.

D. different magmas formed in different locations are isolated and don't mix.

In this image, volatiles that were driven off of the subducting slab have caused the mantle to melt. What kind of melting does this figure show? A. decompression melting B. compression melting C. heat transfer melting D. flux melting

D. flux melting

Which of the following statements is FALSE? Mafic minerals A. crystallize at a higher temperature than do silicic minerals. B. are rich in iron and magnesium. C. typically crystallize first out of a melt. D. form rhyolite and granite.

D. form rhyolite and granite.

Geologists use composition (mineral content) and texture (grain size) to classify igneous rocks. Use the chart below to provide the name of a mafic rock that cooled slowly. A. granite B. rhyolite C. obsidian D. gabbro

D. gabbro

Which of the following statements is FALSE? Felsic (or silicic) magma A. crystallizes at the lowest temperatures. B. has about 70% silica and little magnesium and iron. C. is likely to form light tan, pink, or maroon rocks. D. is less viscous than mafic magma.

D. is less viscous than mafic magma.

Identify the FALSE statement. Hot solid rock in the Earth A. may be even hotter than surface lava because of the pressure of overlying rock. B. may melt if volatiles such as water and carbon dioxide are added. C. may melt if heat is transferred to it from hot mantle rock rising up into the crust. D. maintains uniform composition as it melts and becomes magma.

D. maintains uniform composition as it melts and becomes magma.

Which of the following words could NOT be used to describe portions of a rock with a porphyritic texture? A. groundmass B. phenocryst C. plagioclase D. pyroclastic

D. pyroclastic

Geologists use mineral composition to help categorize igneous rocks. From the information provided in the chart, which minerals would you expect to find in granite? A. olivine, pyroxene, and biotite B. plagioclase, pyroxene and quartz C. k-feldspar biotite and olivine D. quartz, k-feldspar and plagioclase

D. quartz, k-feldspar and plagioclase

Magma may cool and crystallize to become solid igneous rock A. when its volatile content increases. B. more slowly in the presence of circulating groundwater. C. faster if the surface area of the intrusion is low. D. very slowly (centuries to a million years) when it forms a deep pluton.

D. very slowly (centuries to a million years) when it forms a deep pluton.

Bowen's reaction series A. shows the sequence in which different sulfate minerals form during the progressive cooling of a melt. B. creates a progressively more mafic melt. C. has a continuous track in which there is observed a progressive change from sodium-rich to calcium-rich amphibole. D. was established by laboratory experiments in which mafic melt was quenched in mercury.

D. was established by laboratory experiments in which mafic melt was quenched in mercury.