Metamorphism and Deformation Flashcards
the force applied per unit area
- unit of measurement: N/m squared or Pascal
- can exist without strain
stress
change in rocks due to different types of stress; deformation per unit area
- unitless; change in L over L
- cannot exist without stress
strain
types of stress
uniform and differential stress
the forces that act uniformly/equally from all directions; aka pressure
e.g. confining stress/pressure
uniform stress
the weight of overlying rocks that
exert pressure
confining pressure
stress where the forces are not equal
from all directions
differential stress
types of differential stress and its effect
tensional, compressional, and shear stress
- rocks get deformed
this differential stress happens when pieces of rock are pulled apart.
- produces normal fault
tensional stress
occurs when two blocks of rock move toward and push against one another
- produces a reverse fault
compressional stress
when slabs of rock slide past each other horizontally in opposite directions. The rocks are not smashed into each other or pulled apart, but their edges slide along each other with a lot of friction.
- produces a strike-slip fault
shearing stress
stages of deformation
- elastic deformation stage
- ductile deformation stage
- fracture stage
stage of deformation where the strain is reversible
elastic deformation stage
stage of deformation where the strain is irreversible/permanent; without breaking
ductile deformation stage
stage of deformation where the strain is irreversible/ permanent; rocks break
fracture stage
a material that does not return to its original shape after it is deformed
e.g. rocks
inelastic
type/behavior of materials
- affects deformation
brittle and ductile
materials that have a small or large region of elastic behavior but only a small region of ductile behavior before they fracture
brittle materials
materials that have a small region of elastic behavior and a large region of ductile behavior before they fracture
ductile materials
factors that affect the behavior of the material
temperature, confining pressure, strain rate, type of materials/composition
- at high temperature, molecules and their bonds can stretch and move, thus materials will behave in a more _____ manner
- at low temp, materials are _________
ductile, brittle
- at high confining pressure, materials are less likely to fracture (__________)
- at low, the material will be ______ and tend to fracture sooner
ductile, brittle
- at high strain rates, materials tend to fracture (___________)
- at low, more time is available for individual atoms to move, thus _______ behavior is favored
brittle, ductile
quartz and olivine behavior
brittle
clay minerals such as calcite behavior
ductile
water appears to weaken the chemical bonds and forms films around mineral grains
wet rock - ____________
dry rock - ______________
ductile, brittle
effects of deformation
joints, folds, faults, metamorphism
natural cracks on the surface produced by brittle deformation due to tensional stress
joints
contortion of rock layers forming wave-like curves due to ductile deformation caused by compressional stress
folds
- planar fracture on rocks caused by differential stress
faults
the process that occurs when rocks change their form into a new one without undergoing melting or disintegration
* size, shape, and arrangement of grains in the rocks may change (physical) or new minerals may grow (chemical)
metamorphism
original rock of metamorphism
protolith
factors of metamorphism
temperature, pressure chemically-active fluids, parent rock
why shouldn’t the rock melt or disintegrate during metamorphism
because it will become magma
endogenic metamorphism
regional, contact, hydrothermal, cataclastic/dynamic
exogenic x endogenic metamorphism
burial
exogenic/extraterrestrial metamorphism
shock
occurs due to pressure and heat applied to rocks by converging plates and mountain building
- produce a large volume of metamorphic rocks
- high pressure and temperature but low water
regional metamorphism
occurs due to heating (“baking”) of country rocks by rising magma (magma intrusion)
- high temperature, no added pressure; fluids may be present from groundwater reservoir or seafloor
- examples: marble, quartzite, and hornfels
contact metamorphism
driven by hot fluid, commonly water
- addition of fluids promotes recrystallization (change in size and shape of minerals, physical) and neocrystallization (formation of new minerals by
chemical reaction with fluids)
- occurs in oceanic ridges (diverging plates), subduction zone (converging plates), and groundwater near magma chamber
- Example: serpentine; blueschist
hydrothermal metamorphism
due to the shearing of plastic-like rocks near the fault line; example: mylonite
cataclastic/dynamic
due to the confining pressure of overlying rocks and the increasing temperature and pressures at the deeper portion of the crust; example: metaconglomerate
burial
due to the pressure brought by the impact of extraterrestrial objects
(i.e. meteorites); metamorphic rocks formed are called impactite
shock
two types of metamorphic rocks
foliated and non-foliated
type of metamorphic rock
Minerals are aligned in parallel layers and form bands
- Rocks commonly form flakes when they break
foliated
type of metamorphic rock
Minerals are aligned in parallel layers and form bands
- Rocks commonly form flakes when they break
foliated
type of metamorphic rock
Minerals are randomly oriented and usually have
granular appearance
- Rocks do not flake in thin layers when they break
non-foliated
with increasing temp and pressure, metamorphic grade also _____________. the higher the metamorphic grade, the more _____ the rock will be from its original form
increases, changed
