GEOS - 6. Metamorphic Rocks
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What is the geothermal gradient?
rate of increase of temperature w/ depth
What are migmatites?
Rocks that exhibit characteristics of both igneous and metamorphic rocks
What does metamorphism mean?
change of form
What does metamorphism involve?
re-crystallization without heat using heat and/or pressure and/or fluid chemistry
What happens to a parent rock's chemical composition when it undergoes metamorphism?
it is mostly unchanged.
What happens to a parent rock's structures when it undergoes metamorphism?
It is mostly destroyed
What is mesatomatism?
Chemical alteration of a rock by fluids; fluid carries elements into/out of rock
What is an example of mesatomatism?
Hydrothermal fluid flow creates most metallic ore deposits.
Why are metamorphic rocks at the surface not reverse-metamorphosed?
Minerals were formed and stable only at depth. Chemistry happens faster when warmer.
What are the four types of metamorphism?
What is regional metamorphism caused by?
Heat & pressure
How deep into the crust must regional metamorphism occur?
at least 10 km
What plat tectonic settings does metamorphism occur?
Mountain building, thickening crust, subduction
How/where does contact metamorphism occur?
When magma is near cooler rock, the edge of the cool rock is heated near the boundary.
What is contact metamorphism caused by?
What plate tectonic settings does contact metamorphism occur?
Metamorphic aureole = zone of altered rock
How/where does dynamic metamorphism occur?
Folding & faulting is sufficient to crush and pulverize minerals along a fault plane
What does hydrothermal mean?
Flow of hot fluids
What plate tectonic settings does dynamic metamorphism occur?
What is foliation?
The parallel orientation of mineral grains w/in a metamorphic rock
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
What is a geotherm?
Temp vs. depth profile
Where does high pressure and low temperature occur?
Where does high temperature and low pressure occur?
What is the temp vs. depth profile in the upper crust?
25-30 degrees C / km
What are index minerals used for?
They tell us what temperature and pressure that the rock was exposed to
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
- 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
- medium grade
- coarser grain size than slate
- big crystals (typically micas)
- all parallel to one another
- breaks easily
- 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
If a rock has felsic minerals, it will not ___.
- Describe granulite.
- parent rock: gneiss
- beyond melting point of quartz
- Parent rock: quartz sand
- crystals have regrown into each other
- Parent rock: limestone
- nothing but calcite
- Has growing crystals at a solid state
___ and ___ are the most common nonfoliated metamorphic rocks.
How strong is unfractured metamorphic rock?
Is unfractured metamorphic rock permeable?
How do engineers incorrectly define crystalline as?
Plutonic and metamorphic = strong (they ignore foliation and fracturing)
Which metamorphic rocks are used as contruction materials?
Marble, quartzite, gneiss, slate
SLow metamorphic crystal growth creates ___.
What does hydrothermal circulation create?
Most metals & other ores
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