Q&A Hero

Q: In which geologic setting is the most widespread occurrence of hydrothermal metamorphism found? A) Subduction zones between oceanic and continental plates B) Along the axis of a mid-ocean ridge system C) Along transform plate boundaries D) Where mantle plumes interact with the bottom of continental plates

Q: ________ metamorphism tends to occur in regions where massive amounts of sedimentary or volcanic materials accumulate in a subsiding basin, pushing older rocks further into the interior. A) Contact B) Hydrothermal C) Burial D) Regional

Q: Which style of metamorphism will be generated by a magma pluton? A) Contact B) Subduction zone C) Burial D) Regional

Q: Which of the following scenarios best describes the formation of hornfels? A) Mudstones are metamorphosed by directed pressure. B) Granite is melted and recrystallized. C) Shales and mudstones are baked during contact metamorphism. D) Phyllite is altered by contact with hydrothermal fluids.

Q: Which of the following is not an environment of metamorphism? A) Contact with a hot magma body B) Hot fluids coming off a diaper C) Slow cooling of a magma D) High pressure in a subduction zone

Q: Metamorphic rocks can sometimes contain unusually large grains surrounded by a fine-grained matrix of other minerals. These large crystals are called ________. A) vesicles B) phenocrysts C) inclusions D) porphyroblasts

Q: Physical rotation of platy minerals will contribute most to the development of foliation in ________ grade metamorphism. A) low- B) medium- C) medium-high- D) high-

Q: Which of the following is not an example of foliation? A) Parallel alignment of flattened mineral grains or pebbles B) Compositional banding in which the separation of light and dark minerals creates a layered appearance C) Rock cleavage where rocks can be easily split into tabular slabs D) Recrystallization of spherical minerals to create layers parallel to the direction of greatest stress

Q: What is foliation? A) Intergrown mineral crystals formed from cooling magma B) Randomly oriented mineral crystals placed due to confining pressure C) Thin, parallel layers of clay sediments that have been compressed D) Roughly parallel layers of mineral crystals aligned perpendicular to the direction of pressure

Q: What kind of force will create foliation in metamorphic rocks? A) Tension B) Compression C) Shear D) Brittle

Q: Generally speaking, how does the chemical composition of most metamorphic rocks compare to that of the parent rock? A) Their chemical composition will be nearly the same. B) In order to be a metamorphic rock, the chemical composition must change by 50 percent. C) There will be a complete compositional change. D) Knowing the chemical composition is not necessary to understand metamorphic rocks.

Q: What is the definition of metasomatism? A) The rearrangement of ions already present due to changes in heat B) The lengthening of mineral crystals due to directed pressure C) The change in chemical composition because hot fluids are bringing or removing ions D) The more compact organization of mineral crystals due to confining pressure

Q: ________ is the process by which new mineral grains larger than the original mineral grains form as a result of metamorphic heat. A) Recrystallization B) Foliation C) Dissolution D) Metasomatism

Q: Which of the following rocks represents the highest grade of metamorphism? A) Biotite schist B) Quartzite C) Phyllite D) Gneiss

Q: Which of the following lists of metamorphic rocks places the rocks in order from lowest metamorphic grade to highest? A) Gneiss, slate, phyllite, schist B) Anthracite, hornfels, quartzite, marble C) Slate, phyllite, schist, gneiss D) Ironstone, sandstone, slate, gneiss

Q: Which low-grade metamorphic rock displays thin, parallel layers and contains very fine grains of mica? A) Schist B) Gneiss C) Anthracite D) Slate

Q: If clay minerals in a sedimentary rock were buried at a depth where subsurface temperatures exceeded 200C, which common metamorphic mineral would they become? A) Quartz B) Muscovite C) Amphibole D) Plagioclase

Q: Which of the following is the parent rock of quartzite? A) Limestone B) Conglomerate C) Granite D) Sandstone

Q: What is the definition of a parent rock? A) The rock that was altered by metamorphism B) The resulting precipitate when water dissolves mineral matter C) The rock produced by metamorphism D) The igneous rock forming through solidification of magma

Q: ________ is the process by which a rock changes form or mineral content as a result of environmental changes such as heat and pressure. A) Rifting B) Precipitation C) Metamorphism D) Foliation

Q: At what temperature and pressure would kyanite, sillimanite, and andalusite form simultaneously? A) 600C and 2 kilobars B) 700C and 1 kilobar C) 800C and 6 kilobars D) 500C and 4 kilobars

Q: If shale is buried to a depth of 20 km and the temperature is raised to 450C, which mineral would form according to the image above? A) Andalusite B) Kyanite C) Sillimanite

Q: Using the images above, select the correct name for each metamorphic rock and match it with the correct image. Then, select the correct metamorphic grade for each rock. A) Schist, medium B) Gneiss, high C) Slate, low D) Phyllite, low 1. A 2. B 3. C 4. D

Q: You have been asked to review a manuscript that has been submitted for publication in a professional journal. The area of interest in this article is an amphibolite exposed along the Chippewa River at Jim Falls, Wisconsin. The researchers state that the amphibolite is believed to have been altered 2.6 billion years ago by tectonic pressures of 14 kilobars and temperatures of 190C. Should you approve this manuscript for publication? Why or why not?

Q: What is the minimum depth at which subduction zone metamorphism will occur? A) 0 km B) 30 km C) 25 km D) 13 km

Q: What is the temperature range over which hydrothermal metamorphism will occur? A) 0-400C B) 400-1000C C) 200-600C D) 600-750C

Q: What kind of metamorphism will occur if the temperature is 800C and the depth of metamorphism is 7 km? A) Hydrothermal B) Contact C) Regional D) Subduction zone

Q: What kind of metamorphism will occur if the environmental conditions are 400C and 5 kilobars? A) Hydrothermal B) Contact C) Regional D) Subduction zone

Q: What degree of foliation is exhibited by the metamorphic rock in the image above? A) Schistosity B) Nonfoliation C) Gneissic banding D) Slaty cleavage

Q: What is the name of the metamorphic rock in the image above? A) Slate B) Shale C) Gneiss D) Schist

Q: What is the parent rock of the metamorphic sample displayed? A) Limestone B) Quartz sandstone C) Shale D) Granite

Q: What is the texture of this rock? A) Schistosity B) Nonfoliated C) Slaty cleavage D) Gneissic banding

Q: Assume that this foliated rock is oriented so that north is at the top of the image. From which compass directions is the greatest differential stress coming? A) North and south B) North and east C) South and west D) West and east

Q: Which kind of stress (confining pressure or differential stress) is responsible for creating the texture visible in this rock? A) Confining pressure B) Differential stress

Q: What is the name of this rock? A) Slate B) Quartzite C) Schist D) Gneiss

Q: Which agent of metamorphism was primarily responsible for generating the rock in the image above? A) Heat B) Directed pressure C) Confining pressure D) Partial melting

Q: What is the name of this rock? (Hint: It can scratch glass.) A) Slate B) Quartzite C) Marble D) Gneiss

Q: Marble and quartzite can be similar in appearance. Name two simple ID techniques that can be used to differentiate between the two.

Q: Slate and phyllite are similar in appearance. How can the foliation and the shine be used to tell them apart?

Q: What are the four agents of metamorphism?

Q: Define metamorphic grade.

Q: Explain how migmatites form. Why are they difficult to fit into any of the three basic rock types?

Q: How can a meteorite impact metamorphose a rock? What temperature/pressure conditions will be present?

Q: Compare and contrast how the aureole of contact metamorphism will change in thickness depending on the intrusive igneous structure.

Q: What is gneissic banding, how does it form, and how does it compare to the color banding that is often found in marble?

Q: Compare and contrast confining pressure and compressional stress relating to metamorphic rocks. What will happen to the mineral crystals in each situation? Also, provide examples of geologic environments where such pressure would be the main agent of metamorphism.

Q: What role does heat play in creating new minerals or new crystalline structures in metamorphic rocks?

Q: Match the index mineral with the correct metamorphic grade(s). For these purposes, please remember that for a mineral to be part of two metamorphic grades, it should make up at least one-third of both grades. A) Low grade B) Low to medium grade C) Medium to high D) Medium grade E) High grade 1. Chlorite 2. Staurolite 3. Muscovite 4. Garnet 5. Sillimanite

Q: Match the foliated metamorphic rocks in order from lowest grade to highest grade. (Note: First refers to the lowest grade of metamorphism and fourth refers to the highest grade.) A) Slate B) Phyllite C) Gneiss D) Schist 1. First (lowest level of metamorphism) 2. Second 3. Third 4. Fourth (highest level of metamorphism)

Q: Match the metamorphic rock to the metamorphic grade. (Note: Some answers may be used more than once.) A) High-grade metamorphism B) Low-grade metamorphism C) Medium-grade metamorphism 1. Slate 2. Gneiss 3. Schist 4. Phyllite

Q: Foliated textures are primarily the result of heat. Nonfoliated textures are primarily the result of directed pressure.

Q: The geothermal gradient represents a decrease in interior temperature with decreasing distance from the surface.

Q: Metamorphism ends when the rock begins to melt.

Q: Sedimentary rocks are always the parent rocks for metamorphic rocks.

Q: Name three rocks that are produced by contact metamorphism. A) Quartzite, marble, and hornfels B) Marble, schist, and slate C) Slate, phyllite, and gneiss D) Gneiss, quartzite, and anthracite coal

Q: Most metamorphic rocks near the Earth's surface are derived from three common sedimentary rocks. Which three? A) Conglomerate, graywacke, and arkose B) Shale, quartz sandstone, and limestone C) Basalt, travertine, and claystone D) Quartz sandstone, arkose, and siltstone

Q: What are the two main categories of metamorphic texture? A) Heat and pressure B) Schistosity and dissolution C) Vesicular and pyroclastic D) Foliated and nonfoliated

Q: What fluid is generally responsible for metasomatism? A) Sulfuric acid B) Mixed air C) Water D) Petroleum

Q: What is the average increase in temperature along the geothermal gradient in the upper crust? A) 13C per km B) 25C per km C) 30C per km D) 42C per km

Q: What kind of temperature and pressure conditions will exist in a subduction zone metamorphic environment? A) Low temperature and low pressure B) Low temperature and high pressure C) High temperature and low pressure D) High temperature and high pressure

Q: What sedimentary structure is present in this photo? A) Mudcracks B) Graded bedding C) Ripplemarks D) Cross-bedding

Q: What does the presence of mudcracks indicate about the paleoenvironment? A) There was immense pressure placed on these sediments, resulting in stress fractures. B) There was a current of water flowing in one direction. C) Waves were lapping on the shoreline of the ocean. D) There was a wet environment that is drying up.

Q: What sedimentary structure is visible in this image? A) Mudcracks B) Graded bedding C) Ripplemarks D) Cross-bedding

Q: What sedimentary structure(s) can you identify in the above image? A) Ripplemarks and graded bedding B) Graded bedding C) Ripplemarks D) Cross-bedding and graded bedding

Q: What is the sedimentary texture displayed in this image? A) Clay-sized B) Crystalline C) Microcrystalline D) Angular

Q: What is the name of the rock in the above image? A) Breccia B) Limestone C) Shale D) Coquina

Q: What level of sorting is visible in the above image? A) Well sorted B) Moderately sorted C) Poorly sorted

Q: Would the rock in the above image be considered a sedimentary breccia or a conglomerate? Why?

Q: How would you describe the shape of the sediments in the rock in the above image? A) Gravel-sized B) Angular C) Rounded D) Well-sorted

Q: What effect would the release of carbon sequestered in carbonates and organic sedimentary rocks have on the planet?

Q: The velocity of moving water controls the sediment it can carry. How will a decrease in water velocity control the size of the sediment particle that is deposited first?

Q: List three common natural cements used in cementation of sedimentary rocks.

Q: What are the three categories of sedimentary rocks?

Q: List three major energy resources that are derived from sedimentary rocks.

Q: The Grinnell Formation in Glacier National Park contains mudcracks that date back nearly 1.5 billion years. How can delicate sedimentary structures such as these be preserved?

Q: The River Loop Trail at Black Hawk State Historic Site in Rock Island, Illinois, has exposures revealing nearly 130 million years of geologic history. At the base of the hill is Devonian-aged limestone containing brachiopods and bryozoans. Above the limestone is Pennsylvanian-aged shale, with an unconformity between the two. The black shale is rich with fossils of ferns and marsh grasses. Directly on top of the shale is Pennsylvanian-aged sandstone. Using the geologic materials described, determine the environment of deposition for each unit. How has the overall environment changed from the Devonian to the end of the Pennsylvanian?

Q: When studying sedimentary rocks, it is important to understand their environment of deposition. What is the environment of deposition and how can it contribute information about the geologic history of the rock?

Q: If coal is composed of organic materials such as vegetation, what prevents them from decaying before they become a sedimentary rock?

Q: Compare and contrast how the formation of biochemical sediments differs from the formation of inorganic sediments. (Note: The term inorganic sediments refers to those formed in chemical sedimentary rocks.)

Q: Consider the shallow ocean basins and current climate in the Persian Gulf. What kind of rocks would you expect to be forming there, and how would they form?