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What is the geothermal gradient?
rate of increase of temperature w/ depth
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What are migmatites?
Rocks that exhibit characteristics of both igneous and metamorphic rocks
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What does metamorphism mean?
change of form
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What does metamorphism involve?
re-crystallization without heat using heat and/or pressure and/or fluid chemistry
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What happens to a parent rock's chemical composition when it undergoes metamorphism?
it is mostly unchanged.
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What happens to a parent rock's structures when it undergoes metamorphism?
It is mostly destroyed
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What is mesatomatism?
Chemical alteration of a rock by fluids; fluid carries elements into/out of rock
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What is an example of mesatomatism?
Hydrothermal fluid flow creates most metallic ore deposits.
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Why are metamorphic rocks at the surface not reverse-metamorphosed?
Minerals were formed and stable only at depth. Chemistry happens faster when warmer.
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What are the four types of metamorphism?
- regional
- contact
- dynamic
- hydrothermal
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What is regional metamorphism caused by?
Heat & pressure
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How deep into the crust must regional metamorphism occur?
at least 10 km
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What plat tectonic settings does metamorphism occur?
Mountain building, thickening crust, subduction
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How/where does contact metamorphism occur?
When magma is near cooler rock, the edge of the cool rock is heated near the boundary.
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What is contact metamorphism caused by?
Heat
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What plate tectonic settings does contact metamorphism occur?
Metamorphic aureole = zone of altered rock
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How/where does dynamic metamorphism occur?
Folding & faulting is sufficient to crush and pulverize minerals along a fault plane
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What does hydrothermal mean?
Flow of hot fluids
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What plate tectonic settings does dynamic metamorphism occur?
Fault zones
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What is foliation?
The parallel orientation of mineral grains w/in a metamorphic rock
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What is the difference between foliation and bedding?
Foliation show stresses applied in one direction, not sediment laid on top of one another in layers
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What is a geotherm?
Temp vs. depth profile
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Where does high pressure and low temperature occur?
Subduction zones
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Where does high temperature and low pressure occur?
Near magma
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What is the temp vs. depth profile in the upper crust?
25-30 degrees C / km
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What are index minerals used for?
They tell us what temperature and pressure that the rock was exposed to
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What is a metamorphic facies?
a field in the T vs. P plot - tells us about temperature and pressure; pick up a rock and find its facies to know conditions (T, P, depth) at which it was formed
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Describe slate.
- low grade, most minerals parallel to plane, paper-shaped
- clays & chlorites are platey minerals
- Rock can be broken into thin and strong slabs
- Phyllite included in this grade
- Common roofing material
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Describe schist
- medium grade
- coarser grain size than slate
- paper-shaped
- big crystals (typically micas)
- all parallel to one another
- breaks easily
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Describe gneiss
- high grade
- foliated, but more rounded than planar
- bands of dark and light (mafic & felsic)
- caused by flow of atoms at high temperature and pressure
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If a rock has felsic minerals, it will not ___.
- melt
- Describe granulite.
- parent rock: gneiss
- non-foliated
- beyond melting point of quartz
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Describe quartzite.
- Parent rock: quartz sand
- crystals have regrown into each other
- non-foliated
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Describe marble.
- Parent rock: limestone
- nothing but calcite
- Has growing crystals at a solid state
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___ and ___ are the most common nonfoliated metamorphic rocks.
quartzite, marble
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How strong is unfractured metamorphic rock?
Very.
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Is unfractured metamorphic rock permeable?
Nope.
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How do engineers incorrectly define crystalline as?
Plutonic and metamorphic = strong (they ignore foliation and fracturing)
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Which metamorphic rocks are used as contruction materials?
Marble, quartzite, gneiss, slate
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SLow metamorphic crystal growth creates ___.
Gemstones
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What does hydrothermal circulation create?
Most metals & other ores
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