Studied by 8 peoplemetamorphism definition
changes in minerology and texture in the (usually) solid state due to changing external conditions (Pressure and temperature) after 200C
how are new minerals formed in metamorphism without melting
atoms are moved one by one along grain boundaries to form a new mineral
diagenesis meaning
chemical, physical, and biological changes that affect sediment after initial deposition up to 200C (after 200C is metamorphism)
melting temperature occurance
600-800C, bound after metamorphism where igneous processes typically lie
protolith meaning
starting material for a rock ie parent rock
order of metamorphic progression with increasing temperature and pressure
shale
slate
phyllite
schist
gneiss
migmatite (partially melted)
what happens along the metamorphic progression
new or different minerals appear
folliation appears
increased grain size
driving forces of metamorphism?
heat
pressure
fluids
deformation
lithostatic pressure meaning
pressure induced from rocks
(at deep levels, pressure is equal due to flowing rock)
hydrostatic pressure meaning
pressure induced from liquids
(pressure is equally distributed)
typical geothermal gradient
15C/km
regional metamorphism
metamorphism that occurs over a large scale
heat transfer occurs when rocks heat after thrusting on top of each other which causes lower rocks to heat
contact metamorphism
metamorphism that occurs over small region
magma intrusion heats an area
contact heat transfer is controlled by (3)
size of intrusion
temperature of magma
fluid circulation
heat capacity
adding the same amount of heat and energy to different materials will lead to different increases in temperature
aureole
region of metamorphism surrounding an intrusion
larger intrusion = larger aureole
what affects the size of an aureole (5)
temperature difference btwn intrusion and host
composition of intrusion and host
speed of emplacement
fluid interactions (ground water and magmatic fluids)
shape of intrusion
amount of water as metamorphic progress occurs?
weight precent of water decreases due to dehydration reactions
shale (12-15%) to gneiss (0-1%)
regional deformation
rock texture will changed due to differential stress which produces folliation
contact deformation
since the metamorphism is static, there’s no metamorphic stress and no foliation
fabric definition
the combined effects of mineral reactions and deformation throughout the metamorphic event and the subsequent return of the rock to the terrestrial surface
foliation is a type
crystal settling
early formed crystals piling up at the bottom of a magma chamber
what structure does quartz form in rocks like quartzite in thin section
triple grain bonds
can calcite foliate?
calcite cannot since it does not have a long axis
undulous extinction
texture resulting from a deformed crystal which causes the extinction to be wavy and irregular
when does the reduction of grain size occur
extreme deformity that occurs when lots of heat is applied (mylonites)
what metamorphic rock form is most useful when wanting to know about the temperature and pressure of the area
regional shales/pelites (marine origin)
what metamorphic rock form is most useful when wanting to know about the metabasic rock
basaltic rocks
pelite definition
alumina-rich rock that is sensitive to the metamorphic conditions
can define the general increasing metamorphic grade trend
if a rock is on the border of having either kyanite and silimanite but one has a higher Gibbs energy and the other is lower, which form is taken?
Form with the lower gibbs energy
pelite prograde minerals in order (7)
chlorite
biotite
garnet
staurolite
kyanite
silimanite
k-feldspar
prograde meaning
the grade changes in order from low to high temperature
more common since energy is more available
loss of volatiles occurs here
metabasic rock prograde minerals in order (5)
chlorite
epidote
amphibole
garnet
pyroxene
retrograde meaning
the grade changes in order from high to low temperature
needed stuff for the minerals to revert are gone such as H2O and CO2 during peak metamorphism
what conditions make plagioclase more calcium rich?
increased temperature and pressure
how is the kinetics of the rocks shown?
via texture
metamorphic facies
metamorphic rocks that form under the same pressure and temperature but different protoliths
minerals in amphibolite shale facies
quartz, biotite, muscovite, and garnet
minerals in amphibolite limestone facies
calcite
minerals in amphibolite basalt facies
amphibole, plagioclase, quartz
isograds meaning
lines of constant metamorphic grade where new minerals are seen
metamorphic zone naming
named after highest grade metamorphic mineral between the isograds
metasomatism
fluids passing through rock that bring new elements to replace old ones, changes bulk composition of the rock
porphyroblasts
crystal in metamorphic rock that is significantly larger than other minerals in the rock
garnet and staurolite are common
metamorphic grade
loosely states intensity of metamorphism using the formation of minerals at each stage (ie slate, phyllite…)
conditions needed to form greenschist
regional metamorphism
mid temp and pressure
conditions needed to form blueschist
mid to high pressure
low temp
conditions needed to form zeolite
low temp
low pressure
conditions needed to form eclogite
high pressure
mid to high temp
conditions needed to form hornfels
low pressure
mid to high temp
conditions needed to form amphibolite
mid pressure
mid to high temp
conditions needed to form granulite
mid to high pressure
high temperature
geothermometer meaning
metamorphic reactions that are sensitive to temperature changes so can be used to determine metamorphic temperatures
geobarometers
metamorphic reactions that are sensitive to pressure changes so can be used to determine metamorphic pressures but much less common
skarns
calcsilicate rich rocks that can form Fe-ore deposits
soapstone
mixture of serpentine and talc from the metamorphism of ultramafic igneous rocks
index mineral
a mineral that forms in a metamorphized rock that indicates the minimum pressure and temperature in which the rock forms
Note
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