GEOLOGY REVIEW CH. 7

· Correct Answer is highlighted in Bold.

· 1. Choose the listing that shows the rocks in increasing degrees of metamorphism (from lower- to higher-grade).

o Topic: n/a

o a. migmatite, metaconglomerate, gneiss with mica, gneiss without mica

o b. metaconglomerate, gneiss with mica, gneiss without mica, migmatite

o c. metaconglomerate, gneiss with no mica, gneiss with mica, migmatite

o d. gneiss with no mica, gneiss with mica, migmatite, metaconglomerate

o e. It makes no difference; they’re all examples of high-grade metamorphism.

o Feedback/Reference: Metaconglomerate (recognizable by “flattened” or stretched pebbles) is barely metamorphosed (see Figure 7.8(b)); mica is an indicator of low-grade metamorphism; gneiss is a medium-to-high grade metamorphic rock, and migmatite is sufficiently high grade to have begun melting to form igneous rock.
Section: 7.3, p. 194; Figure 7.5(b), p. 195
Resources: Flashcards; Geology at a Glance: Environments of Metamorphism, p, 221.

· 2. What is the protolith of marble?

o Topic: n/a

o a. quartz sandstone

o b. chert

o c. phyllite

o d. gypsum

o e. limestone

o Feedback/Reference: A protolith is the parent rock that is metamorphosed into a different rock; metamorphosed limestone is marble.
Section: 7.3, p. 195

· 3. Identify the FALSE statement: Hydrothermal fluids

o Topic: n/a

o a. may consist of hot water, steam, and supercritical fluid.

o b. are chemically active solutions, not pure water.

o c. change a rock’s chemical composition, a process known as exhumation.

o d. can be derived from groundwater or magma, or can be the product of metamorphic reactions.

o e. can pick up some dissolved ions and drop off others as they circulate through a rock.

o Feedback/Reference: They do change the chemical composition, but the process is known as metasomatism. Exhumation means that deeply buried rocks can eventually be exposed at Earth’s surface.
Section: 7.2, p. 192

· 4. Which of the following locations could not possibly be part of a shield?

o Topic: n/a

o a. Hawaii

o b. Canada

o c. Southern Greenland

o d. Siberia

o e. India

o Feedback/Reference: Shields are the oldest areas of Earth’s surface; Hawaii is a recently formed hot spot island (refer to Chapter 5).
Section: 7.4, p. 207; Figure 7.11(c), p. 206
Resources: Flashcards

· 5. Identify the FALSE statement: A metamorphic rock

o Topic: n/a

o a. may be composed of different minerals than its protolith.

o b. may have developed metamorphic texture of interlocking grains.

o c. cannot be formed below 1200°C.

o d. took thousands to millions of years to develop.

o e. may have preferred mineral orientation caused by differential stress.

o Feedback/Reference: The upper limit of the metamorphic range is approximately 1200°C. Most metamorphism occurs between 200°C and 850°C.
Section: 7.2, p. 190; Figure 7.8(a), p. 199

· 6. Identify the FALSE statement: Extremely high heat of metamorphism

o Topic: n/a

o a. may be as high as 1200°C.

o b. drives off water, causing high-grade metamorphic rocks to be drier than low-grade.

o c. is necessary to form migmatite.

o d. is necessary to form chlorite.

o e. causes mica to react, lose its identity, and become feldspar or some other water-free mineral.

o Feedback/Reference: Chlorite is produced during low-grade metamorphism and generally reacts with other minerals, and hence has disappeared before high metamorphic temperatures are reached.
Section: Figure 7.8(a), p. 199
Resources: Flashcards

· 7. Mylonite

o Topic: n/a

o a. forms by recrystallization in a fault zone.

o b. is produced by shear stress on softened rock.

o c. has pronounced foliation parallel to the direction of faulting.

o d. forms due to dynamic metamorphism.

o e. All the possible answers are correct.

o Feedback/Reference: All the possible answers are correct.
Section: 7.4, p. 201; Figure 7.9(b), page 201

· 8. Identify the FALSE statement: Shock metamorphism

o Topic: n/a

o a. involves high temperatures and compressional stress.

o b. can be caused by meteorite impact.

o c. causes quartz to recrystallize into coesite.

o d. involves sudden compression.

o e. can turn calcite into its polymorph dolomite.

o Feedback/Reference: Calcite and dolomite have different formulas and therefore are not polymorphs; it is necessary to introduce magnesium (Mg) in order to produce dolomite from calcite.
Section: 7.4, p. 203

· 9. Pick out the rock that is nonfoliated.

o Topic: n/a

o a. hornfels

o b. phyllite

o c. slate

o d. schist

o e. gneiss

o Feedback/Reference: Hornfels is nonfoliated rock because it was formed in the absence of differential stress.
Section: 7.3, p. 195
Resources: Flashcards

· 10. Identify the TRUE statement: Quartzite

o Topic: n/a

o a. is basically a solid mass of interlocking quartz crystals.

o b. breaks around the separate grains of quartz that make it up.

o c. is always either white or gray.

o d. always shows strong compositional banding.

o e. All the possible answers are correct.

o Feedback/Reference: Quartzite is a nonfoliated (no banding) metamorphic rock that may be white, gray, purple, or green; it breaks across, not around, its component grains.
Section: 7.3, p. 195
Resources: Flashcards

· 11. Identify the TRUE statement: Metasomatism

o Topic: n/a

o a. does not require heat in order to occur.

o b. requires hot fluids in order to occur.

o c. cannot occur in cold, dry conditions.

o d. results in a partially melted rock.

o e. requires very high pressure, but needs only low temperatures to occur.

o Feedback/Reference: Requiring high pressure, but needing low temperatures applies to the creation of rare blueschist metamorphic rock in subduction zones, not to retrograde metamorphic rocks.
Section: 7.2, p. 192

· 12. Identify the FALSE statement: Metamorphic facies

o Topic: n/a

o a. are identical to metamorphic mineral assemblages.

o b. are sets of metamorphic mineral assemblages indicative of specific ranges of pressure and temperature.

o c. each contain several metamorphic rock types with different mineral content.

o d. are subdivided into seven major categories.

o e. are more reliable indicators of metamorphic conditions than index minerals are.

o Feedback/Reference: The different rocks within a single metamorphic facies do not all have the same mineral assemblages. The specific mineral assemblage present within a metamorphic facies depends upon the bulk chemistry of the rock (see Box 7.1, Metamorphic Facies, p. 216).
Section: Box 7.1, p. 200
Resources: Flashcards

· 13. Identify the TRUE statement about metamorphic rocks and their characteristic environments:

o Topic: n/a

o a. Gneiss is most common in metamorphic aureoles surrounding plutons.

o b. Mylonites are found along convergent-plate boundaries where magma is rising.

o c. Slate, phyllite, schist, and gneiss are found in areas of continental collision.

o d. Blueschists form near mid-ocean ridges.

o e. All the possible answers are correct.

o Feedback/Reference: Gneiss, a foliated metamorphic rock, requires shearing stress to form; plutons don’t cause shearing and they create nonfoliated rock. Mylonites form due to shearing stress along faults deep in the crust, not the heat of convergent boundaries. Blueschists form where there’s extreme pressure and low heat, which does not describe mid-ocean ridge conditions.
Section: 7.4, p. 202; Figure 7.8(a), p. 199
Resources: Geology at a Glance—Environments of Metamorphism, pp. 220–221

· 14. Identify the FALSE statement: Shields

o Topic: n/a

o a. are composed of the oldest rock on Earth.

o b. are composed of extensive areas of sedimentary layers laid down on lava flows.

o c. are large areas where the ground surface is metamorphic rock.

o d. make up large areas of Canada, northern Europe, and South America.

o e. are composed of rocks that were metamorphosed during Precambrian mountain-building events.

o Feedback/Reference: Any sedimentary layers or lava flows that might have been present have eroded away, exposing the deep, ancient metamorphic rock of the shield.
Section: 7.4, p. 207
Resources: Flashcards

· 15. Which of the following processes results in the exposure of deeply buried rocks at the Earth’s surface?

o Topic: n/a

o a. exhalation

o b. metasomatism

o c. ductile deformation

o d. diagenesis

o e. exhumation

o Feedback/Reference: The prefix ex means, to leave. Exhalation means, to breathe out, and diagenesis refers to post-decompositional alteration of sediment, and ductile deformation and metasomatism are both processes related within the realm of metamorphic or structural alteration of rock. Exhumation means, to unbury and refers to the exposure at ground surface of formerly, deeply buried rocks.
Section: 7.4, p. 206; Figure 7.10, p. 203

· 16. Which is NOT a common process by which metamorphic rocks are formed?

o Topic: n/a

o a. pressure solution

o b. plastic deformation

o c. phase change

o d. recrystallization

o e. schistosity

o Feedback/Reference: Schistosity is not a process; it’s the type of foliation in schists that results from the preferred orientation of large mica flakes.
Section: 7.3, p. 194

· 17. Identify the FALSE statement: The sediments in a subsiding sedimentary basin

o Topic: n/a

o a. experience increased pressure and temperature.

o b. undergo diagenetic changes when they’re at shallow depth.

o c. undergo burial metamorphism when they reach depths greater than 8 to 15 km.

o d. can become metasomatized to migmatite.

o e. lose any oil they might contain because metamorphic conditions destroy organic molecules.

o Feedback/Reference: Metasomatism does not create migmatite.
Section: 7.2, p. 192
Resources: Flashcards

· 18. Mountain building due to convergent-margin tectonics and to continental collision

o Topic: n/a

o a. can send surface rock to great depths.

o b. can metamorphose former surface rock by proximity to magma.

o c. can metamorphose former surface rock by increased pressure.

o d. can metamorphose former surface rock by differential stress generated by plate interactions.

o e. All the possible answers are correct.

o Feedback/Reference: All the possible answers are correct.
Section: 7.4, p. 207
Resources: Geology at a Glance—Environments of Metamorphism, pp. 220–221.

· 19. Shear is the opposite of compression—it is to pull something apart (tension).

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Shear is the movement of one mass of material past (or alongside another mass of material). Pulling apart is tension (or extension).
Section: 7.2, p. 192; Figure 7.3, p. 193

· 20. Recrystallization occurs because thermal energy causes atoms to vibrate rapidly, break existing chemical bonds, and migrate to new positions on the crystal lattice where they are more stable under the hotter conditions.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: This process doesn’t change the identity or chemical composition of the mineral; it just produces larger crystals of the mineral.
Section: 7.1, p. 190

· 21. Roofers use the rock schist to shingle roofs because its foliation, called schistosity, causes it to break in convenient size.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: They use slate because cleavage causes it to break into suitable thicknesses for use as roof shingle.
Section: 7.3, p. 194; Figure 7.4(a), p. 194
Resources: Figure 8.7

· 22. The mineral sillimanite indicates higher-grade metamorphism than staurolite.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Sillimanite, staurolite, and kyanite are polymorphs of aluminum silicate, and each has a defined pressure-temperature field of stability. Sillimanite is stable at higher metamorphic grade than staurolite.
Section: Figure 7.5, p. 195

· 23. Schist is a medium-grade foliated metamorphic rock that should contain micas.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Many different types of rocks are composed of atoms that can be metamorphosed into the mineral mica, which is a chief component of the metamorphic rock schist.
Section: 7.3, p. 194

· 24. Which is NOT a cause of banding in gneiss?

o Topic: n/a

o a. preferential orientation

o b. original bedding in a preexisting rock

o c. extensive shearing

o d. migmatite formation

o e. metamorphic differentiation

o Feedback/Reference: Preferential orientation can impart foliation to a rock but cannot cause the compositional banding that defines a gneiss.
Section: 7.3, p. 194
Resources: Flashcards

· 25. Marble is a favorite material of sculptors because of its relative softness, and uniform texture.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Marble is a favorite media of sculptors because it is often very uniform in texture, and can be worked with steel tools. At a finer scale, the equant nature of calcite and dolomite—the minerals that make up marble—impart uniformity in all directions. Think about what it would be like trying to sculpt a highly foliated rock like a slate or schist. Also imagine what it would be like trying to sculpt quartz or quartzite, which are harder than steel and would destroy normal tools.
Section: 7.3, p. 197
Resources: Flashcards

· 26. Metamorphic zones are regions between isograds named after the index minerals that occur within them.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Index minerals are those that indicate the varying conditions within the different zones of the metamorphosed region.
Section: 7.3, p. 198
Resources: Figure 7.8(c); Flashcards

· 27. Blueschist is a common metamorphic rock of continental shields.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Blueschist is a rare, blue-colored rock formed under high-pressure, low-temperature conditions that are found in accretionary prisms adjacent to subduction zones.
Section: 7.4, p. 203
Resources: Geology at a Glance—Environments of Metamorphism, pp. 220–221.

· 28. If the intrusion of magma (a pluton) melts mafic country rock, the resulting metamorphic rock is a schist or gneiss.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: This was a sneaky question! If the intrusion of magma and formation of a pluton melts rock, you’re no longer dealing with a metamorphic rock.
Section: 7.3, p. 198

· 29. Metamorphic aureoles typically contain nonfoliated rock like hornfels, because the pluton intrusion provides heat but not the shearing stress necessary for foliation.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Differential stress is not associated with thermal metamorphism, such as that caused by an adjacent magma body.
Section: 7.3, p. 198
Resources: Flashcards

· 30. In Massachusetts and Connecticut, you can see both unmetamorphosed and high-grade metamorphic rocks.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: These states consist mostly of regionally metamorphosed rock, though each also contains unmetamorphosed sedimentary rocks that formed in basins formed when Pangaea began to rift apart—eventually forming the Atlantic Ocean. These sedimentary basins lie within a one to two hour car drive of high-grade metamorphic rocks found further east.
Section: Figure 7.8(c), p. 199
Resources: Flashcards

· 31. A supercritical fluid permeates rock very thoroughly because it has characteristics of both liquid and gas.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: The extremely high temperatures and pressures of supercritical fluids enable them to intrude like a gas and react with the material like a liquid.
Section: 7.2, p. 192

· 32. Which of the following is NOT required for pressure solution to occur?

o Topic: n/a

o a. uneven (differential) stress

o b. the presence of fluid

o c. grain-to-grain contact

o d. migration of atoms or ions

o e. greenschist-facies conditions or higher

o Feedback/Reference: Pressure solution requires uneven stress (usually the weight of burials), grain-to-grain contacts—fluid within pores, or along grain contacts—and of course, the migration of atoms or ions. Pressure solution does not require greenschist-facies (low grade) metamorphism to occur.
Section: 7.1, p. 190; Figure 7.2(c), p. 192
Resources: Figure 7.2(c)

· 33. When geologists say metamorphic grade, they’re referring to the general degree of metamorphism of a rock; when they say facies, they mean a subset of the broad temperature and pressure conditions in which metamorphism can occur.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: These terms are related to one another, and yet not the same. Metamorphic facies is a more specific descriptor of metamorphism than metamorphic grade. There are eight to twelve metamorphic facies depending on which experts’ classification system you use, and your book shows one of the common classifications of facies. In contrast, metamorphic grade usually consists only of three simple categories: low, medium, and high.
Section: Box 7.1, Metamorphic Facies, p. 200
Resources: Flashcards

· 34. The sequence of increasing metamorphism of the protolith shale (a sedimentary rock) is slate, phyllite, schist, and gneiss.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Metamorphism increases as temperature and pressure increase, and this is the sequence of tocks a shale would transform through, eventually becoming gneiss at very high temperature and pressure.
Section: Geology at a Glance, p. 204-205.
Resources: Geology at a Glance—Environments of Metamorphism, p. 204.

· 35. Dynamothermal metamorphism (regional metamorphism) produces metamorphic rocks in the depths of mountain ranges, which erosion eventually exposes as “mountain roots” hundreds of kilometers wide and thousands of kilometers long.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Continent-to-continent collision results in thickened crust over regions as extensive as the modern Himalayas. Physical weathering tears and wears the tops of such mountain ranges away and isostatic compensation lifts new material upwards. In this way, long-halted former continental collision zones such as the modern Appalachians expose zones of low to high-grade dynamothermally-metamorphosed rock for distances that may be thousands of kilometers in length and hundreds of kilometers in width.
Section: 7.4, p. 202; Figure 7.10, p. 203
Resources: Geology at a Glance—Environments of Metamorphism, pp. 220—221.

· 36. Dissolved ions freed during the process of metasomatism can precipitate to form mineral-filled cracks called veins.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Hydrothermal fluids dissolve the ions, which are then free to relocate either in veins in the Earth or on its surface.
Section: 7.2, p. 192
Resources: Flashcards

· 37. The alignment of equant grains results in preferred orientation.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Equant grains have generally similar dimension in whatever orientation they are measured. For example, platy or elongate grains (or crystals) are not equant (termed inequant). Because of this, equant grains cannot align well, and rocks composed of them cannot generally carry preferred orientations
Section: 7.2, p. 192

· 38. Foliation occurs along bedding planes.

o Topic: n/a

o a. True

o b. False

o Feedback/Reference: Foliation typically does not occur along bedding planes, because it is typically caused by shearing and/or metamorphic conditions that usually do not have the same orientation as bedding.
Section: 7.3, p. 193; Figure 7.4, p. 194

· 39. Contact metamorphism occurs when

o Topic: n/a

o a. two or more minerals that were stable under a former temperature and pressure are unstable (and react) during metamorphism at a different temperature and pressure.

o b. hydrothermal fluids precipitate minerals into joints or other spaces.

o c. hydrothermal fluids alter rock chemistry by removing or adding constituents.

o d. two masses of rock slide by one another along a fault plane.

o e. a mass of rock is affected by the heat of a magma.

o Feedback/Reference: Think of contact metamorphism as what happens if you accidentally touch a very hot stove surface—your skin is altered by a transient (rapidly passing) rise in temperature.
Section: 7.4, p. 198

· 40. Which process would you most expect during hydrothermal metamorphism near a mid-ocean ridge?

o Topic: n/a

o a. foliation

o b. pressure solution

o c. dynamothermal metamorphism

o d. metasomatism

o e. dynamic metamorphism

o Feedback/Reference: Metasomatism is the alteration of a rock’s composition due to the interaction with very hot aqueous (water) solutions, i.e., hydrothermal solution.
Section: 7.2, p. 192

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