GEOL 101 Chapter 8

25 July 2022
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question
How are metamorphic rocks formed?
answer
Preexisting rock is altered through heat and pressure.
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Do metamorphic rocks look like the preexisting rock from which they form?
answer
Sometimes, but not always
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What is foliation?
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Banding in metamorphic rocks that results from the reorientation of minerals.
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How will foliation in continental metamorphic rocks formed during subduction be oriented?
answer
Perpendicular to the direction of plate movement.
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What would you call a granite that has undergone metamorphism and now exhibits foliation?
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Gneiss
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What is rock texture?
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The way the rock looks.
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How will minerals orient when a rock is put under normal stress?
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Perpendicular to the direction of the greatest stress.
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How will minerals grow when a rock is put under normal stress?
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Perpendicular to the direction of the greatest stress.
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How will minerals orient when a rock is put under shear stress?
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Parallel to the direction of the shear stress.
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Why do bands of minerals form when rocks are put under normal stress?
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Minerals dissolve, atoms migrate to new locations, and minerals reform.
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Why are mineral bands in metamorphic rocks light and dark colored?
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Dark minerals rich in iron and magnesium separate from light minerals rich in silica and aluminum.
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Which processes result in mineral flattening during metamorphism?
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Dissolution followed by crystallization.
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In addition to mineralogic composition, the degree of metamorphism in a rock is also characterized by _________.
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Texture
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Application of low-grade metamorphic forces to a rock causes _______.
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an increase in rock density.
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What agent might metamorphose rocks found adjacent to a large magma body?
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Hydrothermal solutions
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If foliation is to develop in metamorphic rocks, it occurs best at medium- to high-grade conditions because ________.
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There is enough heat and pressure to induce recrystallization of any tabular minerals in the rock.
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Why does quartzite not exhibit foliated texture?
answer
There are very few or no tabular minerals in quartzite.
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What do we call a metamorphic rock that has microscopic to very fine-grained texture, breaks into slabs or sheets and is dull on the surface?
answer
Slate
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What do we call a metamorphic rock that has a coarse-grained texture, is dominated by mica, and contains no other notable minerals?
answer
Mica schist
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What do we call a metamorphic rock that has coarse-grained texture, minimal amounts of mica, and contains minerals that are segregated into bands?
answer
Gneiss
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Working in the field, you encounter a metamorphic rock that lacks foliation and reacts to hydrochloric acid. How should this rock be classified?
answer
Marble
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Working in the field, you encounter a metamorphic rock that lacks foliation and is composed primarily of interlocking sand-sized grains that will scratch glass. How should this rock be classified?
answer
Quartzite
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Which of the following factors describe the metamorphic conditions at a mid-ocean ridge?
answer
-low temperature -low pressure -hot, watery fluids
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Which of the following factors describe the metamorphic conditions in a subduction zone?
answer
-low temperature -high pressure
question
Which of the following is a metamorphic rock?
answer
Gneiss
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Which of the following is a temperature associated with metamorphism?
answer
400 degrees Celsius
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Which of the following metamorphic rocks could have a parent rock(protolith) of shale?
answer
-gneiss -slate -phyllite -schist
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Which of the following is associated with the metamorphic rock phyllite?
answer
Intermediate-grade metamorphism
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Which of the following factors describe the conditions at a zone where low-grade regional metamorphism is occurring?
answer
-low pressure -low temperature
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Which of the following describes the orientation of the long axes of rocks and mineral grains in relationship to the stress applied?
answer
-the long axis of a rock is parallel to the direction of the weakest stress applied -mineral grains are oriented parallel to the direction of the weakest stress applied.
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From the following choices, identify the grade of metamorphism and one characteristic mineral associated with each of the metamorphic rocks.
answer
SCHIST -intermediate-grade metamorphism -garnet SLATE -low-grade metamorphism -chlorite GNEISS -high-grade metamorphism -sillimanite
question
Which of the following factors describes the conditions at a zone where contact metamorphism is occuring?
answer
-low pressure -high temperature
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What is a metamorphic aureole?
answer
A ring of metamorphic rocks adjacent to an igneous intrusion.
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How is quartz sandstone metamorphosed into quartize during contact metamorphism?
answer
Sand grains are fused together because of high temperatures.
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Which of the following best describes confining pressure and the location in which it occurs?
answer
Moderate pressures at shallow depths.