GEOL 8

25 July 2022
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107 test answers

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Metamorphism can lead to changes in _____.
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mineralogy, texture, chemical composition
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________ is characterized by the segregation of light- and dark-colored minerals into thin layers or bands.
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Granitic gneiss
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At high pressures and elevated temperatures of regional metamorphism, silicate rocks are more resistant to flowage and deformation than at low temperatures and pressures.
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False
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During metamorphic process, the rock essentially remains a _____.
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Solid
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Where does Earth's internal heat come from?
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radioactive decay, energy from earths formation, magma
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Rock cleavage or slaty cleavage in slates is largely a consequence of abundant, parallel-aligned, very fine-grained mica flakes in the rock.
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True
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The altered rocks that form around a molten igneous body are called _____.
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An aureole
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Slate and schist are both derived by metamorphism of shales and mudstones.
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True
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________ is thought to form by partial melting and in situ crystallization of the melted portion.
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Migmatite
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Which low-grade metamorphic rock, composed of extremely fine-sized mica and other mineral grains, typically exhibits well-developed rock cleavage?
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Slate
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Which of the following forms at the highest grade of regional metamorphism?
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Schist
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________ is typically formed by metamorphism of a sandstone.
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Quartzite
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What term describes the zone of contact metamorphism surrounding an intrusive magma body?
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Aureole
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Foliated metamorphic rocks are composed largely of equidimensional grains of minerals such as quartz and calcite.
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False
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What major change occurs during metamorphism of limestone to marble?
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Calcite grains grow larger and increase in size
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What is the major source of heat for contact metamorphism?
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Heat from a nearby magma body
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Amphibolite is a foliated metamorphic rock composed principally of hornblende and plagioclase. How does it form?
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By regional metamorphism of volcanic rocks such as andesite and basalt
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What platy, parallel, mineral grains are the most visual aspect of foliated metamorphic rocks?
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Micas
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Slate is a _____-grade metamorphic rock.
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Low
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Which of the following best describes the conditions of contact metamorphism?
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Pressures are fairly low, the rock is in the upper part of the crust, the heat is supplied from a nearby magma body
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________ forms from the metamorphism of limestone or dolostone.
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Marble
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Carefully examine the photograph below of a metamorphic rock sample. The sample is shown as its actual size.
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Foliated
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Consider how this rock got its texture. Was it compressed from top to bottom or from side to side?
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From top to bottom
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A ________ forms at very high pressures but moderately low temperatures associated with subduction of oceanic crust and sediments.
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Blueschist
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What two, metamorphic rocks are composed predominantly of single minerals?
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Marble and quartzite
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Muscovite, biotite, and chlorite are common minerals found in phyllites and schists.
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True
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_______ is a strong, parallel alignment of coarse mica flakes and/or of different mineral bands in a metamorphic rock.
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Foliation
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Tektites originate in what metamorphic environment?
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High temperature associated with meteorite impacts
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In which setting would regional metamorphism be most likely?
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At great depths in the crust where two continents are colliding
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In confining pressure, forces are applied _______.
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Equally in all directions
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Metamorphic rocks containing garnet are considered to be _______.
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Medium grade
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Slate's parent rock is _____.
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Shale
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Which of the following would exhibit sheared and mechanically fragmented rocks?
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Fault movements at shallow depths
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Three major factors involved in metamorphism are elevated temperature, elevated pressure, and the chemical action of hot fluids.
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True
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Which of the following statements concerning slate is not true?
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Has abundant, coarse-grained mica
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Which texture best describes a metamorphic rock with a planar arrangement of mineral grains?
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Foliation
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High-grade, regional metamorphism produces significant and recognizable changes in the textures and mineral compositions of rocks.
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True
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Partial melting is an important process in the formation of migmatites.
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True
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What foliated, metamorphic rock is texturally intermediate between slate and schist?
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Phyllite
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Calcite is the main mineral constituent of the sedimentary rock limestone and of the metamorphic rock marble.
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True
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metamorphism
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"to change form"; the transition of one rock into another by temperatures and/or pressures unline those in which it formed
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parent rock
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the rock from which a metamorphic rock forms
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metamorphic grade
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the degree to which the parent rock changes during metamorphism
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recrystallization
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the process of forming new, stable minerals larger than the original
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geothermal gradient
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an increase in temperature with depth
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contact metamorphism
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rising mantle plumes
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confining pressure
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forces are applied equally in all directions (analogous to water pressure)
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differential stress
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forces are unequal in different directions
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compressional stress
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rocks are squeezed as if in a vice; shortened in one direction and elongated in the other direction
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chemically active fluids
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enhances migration of ions; aids in recrystallization of existing minerals
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texture
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describes the size, shape, and arrangement of mineral grains
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foliation
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describes any planar arrangement of mineral grains or structural features within a rock
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rock or slaty cleavage
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rocks split into thin slabs; develops in beds of shale with low-grade metamorphism
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schistosity
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platy materials are discernable with the unaided eye; exhibit a planar or layered structure; rocks having this texture are referred to as schist
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gneissic texture
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during high grade metamorphism, ion migration results in the segregation of minerals into light and dark bands; metamorphic rocks with this texture are called gneiss
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nonfoliated metamorphic rocks
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are composed of minerals that exhibit equidimensional crystals and lack foliation; develop in environments where deformation is minimal
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porphyroblastic textures
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unusually large grains, called porphyroblasts, are surrounded by a fine-grained matrix of pther minerals
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contact or thermal metamorphism
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results from a rise in temperature when magma invades a host rock; occurs in the upper crust (low pressure, high temperature); the zone of alteration forms in the rock surrounding the magma
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aureole
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zone of alteration
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hydrothermal metamorphism
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chemical alteration caused by hot, ion-rich fluids circulating through pore spaces and rock fractures; typically occurs along the axes of mid-ocean ridges
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black smokers
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the result of fluids gushing from the seafloor
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burial metamorphism
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associated with very thick sedimentary strata in a subsiding basin (Gulf of Mexico is an example)
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subduction zone metamorphism
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sediments and oceanic crust are subducted fast enough that pressure increases before temperature
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regional metamorphism
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produces the greatest quantity of metamorphic rock; associated with mountain building and the collision of continental blocks
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impact metamorphism
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occurs when meteorites strike Earth's surface; product of these impacts are fused fragmented rock plus glass-rich ejecta that resemble volcanic bombc
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metamorphic facies
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metamorphic rocks that contain the same mineral assemblage and formed in similar metamorphic environments
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protolith
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parent rock that undergoes metamorphism
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recrystallization
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metamorphic process; minerals change shape and size; identity does not change
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recrystallization
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metamorphic process of limestone to marble
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phase change
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metamorphic process; new minerals form with the same chemical formula and different crystal structure
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phase change
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metamorphic process of andalusite to kyanite
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neocrystallization
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metamorphic process; new minerals form from old unstable minerals
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neocrystallization
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metamorphic process of shale to garnet mica schist
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solid
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the state metamorphism always happens in
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200-850
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range of degrees of temperature for metamorphism
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temperature, pressure, differential stress, superheated water
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4 agents of metamorphism
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tension
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type of differential stress; pull apart normal stress
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compression
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type of differential stress; push together normal stress
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shear
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type of differential stress; moves one part of a material sideways
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foliation
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preferred mineral alignment
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perpendicular to compression
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how foliation develops
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preferred inequant mineral orientation or compositional banding
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why foliation occurs
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slate, phyllite, schist, gneiss
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4 foliated rocks increasing in metamorphic grade
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marble and quartzite
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2 non-foliated rocks
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limestone
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protolith of marble
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sandstone
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protolith of quartzite
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metamorphic grade
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measure of metamorphic intensity
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thermal
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type of metamorphic environment; heating by a plutonic intrusion
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burial
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type of metamorphic environment; increases in pressure and temperature by a deep burial in the basin
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dynamic
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type of metamorphic environment; shearing in a fault zone
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regional
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type of metamorphic environment; pressure and temperature alteration due to orogenesis
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hydrothermal
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type of metamorphic environment; alteration by hot water leaching
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subduction
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type of metamorphic environment; high pressure low temperature alteration
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shock
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type of metamorphic environment; extreme high pressure attending a bolide impact
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low grade metamorphism
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low temperatures and low pressures
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high grade metamorphism
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high temperatures and high pressures
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geothermal gradient and contact metamorphism
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two sources of heat
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Nonfoliated
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metamorphic rocks are composed of minerals that exhibit equidimensional crystals and lack foliation
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aureole
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The zone of alteration forms in the rock surrounding the magma
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hydrothermal metamorphism
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Chemical alteration caused by hot, ion-rich fluids circulating through pore spaces and rock fractures
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Burial Metamorphism
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Associated with very thick sedimentary strata in a subsiding basin
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Subduction Zone Metamorphism
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Sediments and oceanic crust are subducted fast enough that pressure increases before temperature
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low pressure and high heat
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Contact or Thermal Metamorphism
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Regional Metamorphism
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Produces the greatest quantity of metamorphic rock and associated with mountain building and the collision of continental blocks
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Impact metamorphism
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Occurs when meteorites strike Earth's surface
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Index minerals
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are good indicators of metamorphic environments
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Metamorphic facies
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Metamorphic rocks that contain the same mineral assemblage and formed in similar metamorphic environments