metamorphic Flashcards
metamorphism
transformation of one rock type to another due to increase in temp and/or pressure
how are metamorphic rocks produced? what are these rocks called?
preexisting igneous, sedimentary, metamorphic rocks (parent rock)
Explain when the rock stops metamorphizing? why does it metamorphize
when it reaches a state of equilibrium with new env.
parent isn’t in equilibrium
what changes happen during metamorphism?
change in mineralogy, texture, or chem comp
where do most metamorphic changes occur?
high temp and pressures of mantle
Low-grade metamorphism
low temps and low pressures produce slight changes
low-grade metamorphism ex
what kind of agent
shale(loosely packed)–> slate (tightly packed)
differnetial stress
high grade metamorphism
high temps and high temps produce substantial changes where parent rock can’t be identified
ex of high grade metamorphism
granodiorite(randomly oriented minerals) –>folded gneiss (segregated and deformed minerals) foliation
metamorphism occurs in 2 settings:
contact metamorphism
regional metamorphism
contact/thermal metamorphism
intruding magma heats adjacent rock to temp for metamorphism
regional metamorphism
rock subjected to high temp and pressure during mt-building and large scale deformation
what are the agents of metamorphism
which are for regional and contact
heat, confining pressure, differential stress, chemically active fluids
contact: heat/magma
regional: pressure and stress
what does the agent: heat, trigger? and 2 sources?
chem reactions sparking recrystallization and formation of new minerals
intruding magma (oven)
buried in depth
Confining pressure
pressure increases with depth since thickness of overlying material is greater and forces applied in all directions
what does confining pressure trigger
recrystallization of new minerals and spaces of grains are closes (more compact), more dense, deformation by decreasing volume
differential stress
rock bodies become highly crumpled bc during mt-building bc of unequal forces in dif directions
rocks exposed to differential stress are shortened in what direction? elongated?
direction of greatest stress
direction perpendicular to greatest stress
surface env with low temp vs high temp response to differential stress
low: brittle
high: ductile (foliations)
chemically active fluids
what do they act as
minerals tend to recyrstallize and grow in what direction
hydrothermal fluid rich in ions
catalysts for recrystallization
perpendicular to compressional stresses
2 types of metamorphism caused by chemically active fluids
changes arrangement and shape of mineral grains
change chem.comp
what is foliation a characteristic of? what is it driven by?
region metamorphic rocks
compressional stress
what are the agents of metamorphism
heat, confining pressure, differential stress, chemically active fluids
Low-grade metamorphism makes rocks
compact and more dense
High-grade metamorphism causes
recrystallization and growth of visible crystals
Foliation
characterisic of what rocks
nearly flat arrangement of mineral grains or structural features
although all rocks can have it, it’s moslty metamorphic
High-grade metamorphism causes
recrystallization and growth of visible crystals
Low-grade metamorphism makes rocks
compact and more dense
what is foliation a characteristic of?
regional metamorphic rock
what is foliation driven by?
compressional stress to develop parallel alignment
ex of Foliation
Parallel alignment of micas
Parallel alignment of flattened pebbles
Compositional banding
Split into tabular slabs
nonfoliated rocks develop in what type of env.
deformation is minimal and parent rocks are made of stable minerals with simple comp
before metamorphism processes vs after
before: confining pressure
after: differiental stress
slate
foliated with rock cleavage, made from volcanic ash or shale
phyllite
glossy sheen and wavy surface
schists
formed by regional metamorphism of shale
gneiss
banded metamorphic rock that may have intricate folds
marble
coarse crystalline rock
From metamorphism of limestone
quartzite
very hard because of fused quartz grains
From metamorphosed quartz sandstone
naming crystals with accessory minerals
add a prefix that represents the accessory mineral (large crystal)
what do metamorphic rocks make up?
c.c and cores of mts
how do the mineral grains behave when under differental stress
r
rotate perpendiculat to direction of max stress
foliated
slate
phyllite
schist
gneiss
what process might be responsible for the formation of the vishnu schist? how does this processs differ from the process that formed sedumentary rock on top
regional metamorphism vs lithification
whaat does the cishcu schist tell you abt tge history of the grandcanyon
used to a mountain
why can we see vishnu shcist
layers of sedimentary rock above it were eroded, so it can existelsewhere except they just werent eroded
