* new or different minerals appear * folliation appears * increased grain size
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driving forces of metamorphism?
* heat * pressure * fluids * deformation
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lithostatic pressure meaning
pressure induced from rocks
(at deep levels, pressure is equal due to flowing rock)
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hydrostatic pressure meaning
pressure induced from liquids
(pressure is equally distributed)
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typical geothermal gradient
15C/km
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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
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contact metamorphism
metamorphism that occurs over small region
* magma intrusion heats an area
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contact heat transfer is controlled by (3)
* size of intrusion * temperature of magma * fluid circulation
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heat capacity
adding the same amount of heat and energy to different materials will lead to different increases in temperature
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aureole
region of metamorphism surrounding an intrusion
* larger intrusion = larger aureole
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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
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amount of water as metamorphic progress occurs?
weight precent of water decreases due to dehydration reactions
* shale (12-15%) to gneiss (0-1%)
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regional deformation
rock texture will changed due to differential stress which produces folliation
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contact deformation
since the metamorphism is static, there’s no metamorphic stress and no foliation
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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
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crystal settling
early formed crystals piling up at the bottom of a magma chamber
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what structure does quartz form in rocks like quartzite in thin section
triple grain bonds
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can calcite foliate?
calcite cannot since it does not have a long axis
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undulous extinction
texture resulting from a deformed crystal which causes the extinction to be wavy and irregular
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when does the reduction of grain size occur
extreme deformity that occurs when lots of heat is applied (mylonites)
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what metamorphic rock form is most useful when wanting to know about the temperature and pressure of the area
regional shales/pelites (marine origin)
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what metamorphic rock form is most useful when wanting to know about the metabasic rock
basaltic rocks
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pelite definition
alumina-rich rock that is sensitive to the metamorphic conditions
can define the general increasing metamorphic grade trend
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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?