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83 Cards in this Set
- Front
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Metamorphism involves the transformation of pre-existing rocks by _____ |
Heat and Pressure |
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The most important agent of metamorphism |
Heat |
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stress |
The force per unit area acting on any surface within a solid. |
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contact or thermal metamorphism |
Changes in rock caused by the heat from a nearby magma body. |
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confining pressure |
equal pressure on all sides creating a more dense rock with less volume |
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Differential stress |
Forces that are unequal in different directions. |
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Contact metamorphism takes place when rocks come in contact with a |
magma body |
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In addition to temperature, which of the following agents increases with depth in Earth |
pressure |
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what chemical active fluid most commonly enhances metamorphism |
Hot water |
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When fine-grained tabular minerals in a rock at depth are subjected to differential stresses, they what |
align perpendicularly to the plane in which the maximum compressive stress is applied |
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At a mid-ocean spreading center, alteration of rocks by chemically active fluids causes metamorphism by __________. |
replacement or substitution of ions in the pre-existing rock |
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Foliation |
A term for a linear arrangement of textural features often exhibited by metamorphic rocks. |
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In addition to mineralogic composition, the degree of metamorphism in a rock is also characterized by _____ |
texture |
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Hydrothermal solution |
The hot, watery solution that escapes from a mass of magma during the latter stages of crystallization. Such solutions may alter the surrounding country rock and are frequently the source of significant ore deposits. |
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Application of low-grade metamorphic forces to a rock causes an increase in what? |
an increase in rock density |
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What agent might metamorphose rocks found adjacent to a large magma body? |
Hydrothermal solution |
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If foliation is to develop in metamorphic rocks, it occurs best at medium- to high-grade conditions because _____. |
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 |
There are very few or no tabular minerals in quartzite |
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What is rock texture |
the way it looks |
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How will minerals orient when a rock is put under normal stress |
perpendicular to the direction of the greatest stress |
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How will minerals grow when a rock is put under normal stress? |
perpendicular to the direction of the greatest stress |
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Why do bands of minerals form when rocks are put under normal stress? |
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 |
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? |
dissolution followed by crystallization |
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What is foliation? |
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 |
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 |
gneiss |
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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? |
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? |
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? |
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? |
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 |
quartzite |
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Which of the following factors describes the conditions at a zone where contact metamorphism is occurring? |
high temperature low pressure |
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What is a metamorphic aureole? |
a ring of metamorphic rocks adjacent to an igneous intrusion or a magma body |
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How is quartz sandstone metamorphosed into quartzite during contact metamorphism? |
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? |
moderate pressures at shallow depths |
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mineralogy |
The study of minerals. |
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metamorphic grade |
The degree to which a parent rock changes during metamorphism and varies from low grade to high grade |
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Metamorphism means to change form. Describe how a rock may change during metamorphism |
changes in the mineralogy, texture, and sometimes the chemical composition of the parent rock |
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Name the 4 agents of metamorphism |
heat, pressure, directional stress, and chemically active fluids |
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The formation of new mineral grains that tend to be larger that the original grains is called what |
recrystallization |
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geothermal gradient |
The gradual increase in temperature with depth in the crust. The average is 30° C per kilometer in the upper crust. |
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Transformation of one mineral to another |
phase change |
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Compressional stress |
Differential stress that shortens a rock body by squeezing a rock mass |
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ductile deformation |
A type of solid-state flow that produces a change in the size and shape of a rock body without fracturing. Occurs at depths where temperatures and confining pressures are high. |
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metasomatism |
the chemical alteration of a rock by hydrothermal and other fluids. |
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Why is heat considered the most important agent of metamorphism |
It provides the energy needed to drive the chemical reactions that that result in the recrystallization of existing minerals |
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What role do chemically active fluids play in metamorphism |
By dissolving and transporting ions from one site in the crystal structure to another thereby facilitating (make action easy) the process of recrystallization |
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Briefly describe 3 ways in which the mineral grains in a rock develop a preferred orientaion |
Rotation of platy mineral grains, recrystallization that produces new minerals, and flattening spherically shaped grains |
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pressure solution |
a process where individual atoms move from a location along the margin of the grain that is highly stressed to less stressed position on the same grain |
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a mineral's crystalline structure slide relative to one another along discrete planes thereby distorting the grain |
Solid state flow |
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name three foliated textures |
rock or slaty cleavage, schistosity, and gneissic texture or banding |
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accessory minerals, some of which are unique to metamorphic rocks |
mica schist |
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an amphibole rich rock that exhibits a gneissic texture is called what |
amphibolite |
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How does the rock gneiss form |
During high grade metamorphism, the light and dark components separate giving the rock a banded or layered appearance |
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rocks that form in aureoles are what |
not foliated (it doesnt involve directional stress) |
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hydrothermal metamorphism |
Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock. (along the mid oceanic ridge) |
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black smokers |
A hydrothermal vent on the ocean floor that emits a black cloud of hot, metal-rich water. |
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burial metamorphism |
Low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata. |
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subduction zone metamorphism |
High-pressure, low-temperature metamorphism that occurs where sediments are carried to great depths by a subducting plate. |
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Metamorphism associated with large-scale mountain building |
Regional metamorphism |
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Fault breccia |
movement along a fault zone fractures and pulverizes rock. the result is a loosely coherent rock called |
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mylonites |
A metamorphic rock deformed by ductile flow. As the fault zone starts to move in opposite directions the minerals in the fault zone tend to form elongated grains that give the rock a foliated appearance. Rocks formed in these zones are called |
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name three rocks that are produced by contact metamorphism |
Hornfels, marble, and quartzite (all nonfoliated) |
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In which of the major types of metamorphism does compressional stress play a major role |
Regional metamorphism |
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what type of plate boundary is associated with regional metamorphism |
continental convergent plate boundary |
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List the common metamorphic rocks generated by regional metamorphism |
Slate, phyllite, schist, gneiss, quartzite and marble |
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Migmatite |
A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored silicate minerals melt and then crystallize, while the dark silicate minerals remain solid. |
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Metamorphic facies |
A group of associated minerals that are used to establish the pressures and temperatures at which rocks undergo metamorphism. |
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Metamorphism that occurs when meteorites strike Earth's surface. |
Impact (or shock) Metamorphism |
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products of impact metamorphism |
Impactiles |
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index minerals |
A mineral that is a good indicator of the metamorphic environment in which it formed. Used to distinguish different zones of regional metamorphism. |
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Migmatites |
A rock exhibiting both igneous and metamorphic rock characteristics. Such rocks may form when light-colored silicate minerals melt and then crystallize, while the dark silicate minerals remain solid. |
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Why are migmatites difficult to place into any one of the three basic rock groups? |
Because it contains both igneous and metamorphic rock characteristics. This is due to the light colored minerals having a lower melting point and they melt giving the rock a igneous characteristic. |
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Name several common metamorphic facies |
Hornfels, zeolite, greenschist, amphibolite, granulite, blueschist, and eclogite facies |
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The name for each metamorphic facies refers to a metamorphic rock derived specifically from a |
basaltic parent |
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a blue colored variety of amphibole |
glaucophane |
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what two physical conditions vary within earth to produce different metamorphic environments |
Temperature and pressure |
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Name the three minerals used to predict metamorphic environments |
Andalusite, Kyanite, and sillimanite |
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Andalusite, Kyanite, and sillimanite these are all examples of what |
polymorphs |
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The metamorphic facies associated with high pressure and low temperature environments is called what |
Blueschist facies |
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The metamorphic facies associated with very high pressure and very high temperature environments is called what |
Eclogite facies |
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Which process most likely leads to the formation of minerals belonging to the hornfels facies- contact metamorphism or regional metamorphism |
Contact metamorphism because hornfel facies develop under high temperature and low pressure environments |
