Week 7 Flashcards
Parent rock (protolith)
The rock before metamorphism
Metamorphic grade
The degree to which a parent rock changes during metamorphism. It varies from low grade (temperature and pressure) to high
Recrystallization
The formation of new mineral crystals in a rock that tend to be larger than the original
Change in shape and size of grains without changing ID of mineral
Noecrystallization
Brand new minerals formed from protolith
Confining pressure
Stress that is applied in all directions
Differential stress
Forces that are unequal in all directions
CONVERGENT PB
Compressional stress
Differential stress that shortens a rock body
Shear stress
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3 types of stress
Differential
Compressional
Shear
Texture (foliation)
Refers to any planar( flat) arrangement of mineral grains or crystals within a rock. Driven by compressional stress. Includes banding/ cleavage
Layers
Non foliation
Tends to be one type. No layers
Where deformation is minimal
Hydrothermal
Contact metamorphism
Changes in rock caused by the heat from a nearby magma body
Hydrothermal metamorphism
Chemical alterations that occur as hot iron rich water circulates through fractures in rock
Enhances recrystallization
Subduction zone (burial) metamorphism
High pressure low temperatures metamorphism that occurs where sediments are carried to great depths by a subducting plate
Types of metamorphic environments
Hydrothermal: low pressure, low to mid temp
Contact: low pressure, low to high temp
Regional: low to high temperature and pressure
Subd zone; high pressure low temp
4 agents that drive metamorphism
Heat
Pressure
Directional stress
Chemically active fluids
How is confining pressure different from differential stress
Confining pressure squeezes rock equally in all directions, differential is greater in one direction than others.
Define foliation
Refers to any planar( flat) arrangement of mineral grains or crystals within a rock. Driven by compressional stress. Includes banding/ cleavage
How does a slate change to a phylite and so on
Goes through regional metamorphism. Low to high grade metamorphism
Slate phylite schist gneiss
What is the agent of hydrothermal metamorphism
Hot iron fluids / water
What type of plate boundary is associated with regional metamorphism
Convergent plate boundary
How does contact metamorphism work
Rocks surrounding a molten igneous body are baked. Alters rock adjacent to the heat source called an aureole.
Regional metamorphism
Metamorphism associated with large scale mountain building
Folding and faulting
Phase change
Transforms one mineral into another. Same composition different structure
Metamorphic rocks
Meta= change from one rock type team another
Altering of any pre existing rock through a solid state Change
Temperatures of metamorphism
200-700 degrees
Causes of metamorphism 4
Heat- subducting lithosphere leads to recrystallization/ne
Pressure: confining/ differential stress. Leads to phase change/ neo
Water- hot water will accelerate processes
Importance of parent rock
Is ductile high or low pressure?
(No fractures) high confining pressure
Fractures- low confining pressure
Read figure 8.3
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Metamorphism
Transforms one rock type into another
Process that changes the mineralogy, texture, and sometimes chemical composition that of a rock
