Chapter 6 - Metamorphismmysite.science.uottawa.ca/hmoha098/Pages/Chapter 6-Metamorphism... ·...
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10/25/2008 1 Understanding Earth Fifth Edition Copyright © 2007 by W. H. Freeman and Company Lecturer: H Mohammadzadeh Assistant professors, Department of Geology, FUM Grotzinger • Jordan • Press • Siever Chapter 6: METAMORPHISM Modification of Rocks by Temperature and Pressure Chapter 6 Chapter 6 Metamorphism: Metamorphism: Modification of Modification of Rocks by Rocks by Temperature Temperature and Pressure and Pressure About Metamorphism About Metamorphism • Changes in heat, pressure, and the chemical environment of rocks can alter Changes in heat, pressure, and the chemical environment of rocks can alter mineral compositions and crystalline textures, making them metamorphic. mineral compositions and crystalline textures, making them metamorphic. • Metamorphic changes occur in the solid state, so there is no melting. Metamorphic changes occur in the solid state, so there is no melting.
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Transcript of Chapter 6 - Metamorphismmysite.science.uottawa.ca/hmoha098/Pages/Chapter 6-Metamorphism... ·...
10/25/2008
1
Understanding EarthFifth Edition
Copyright © 2007 by W. H. Freeman and Company
Lecturer: H MohammadzadehAssistant professors,
Department of Geology, FUM
Grotzinger • Jordan • Press • Siever
Chapter 6:METAMORPHISM
Modification of Rocks by Temperature and Pressure
Chapter 6Chapter 6Metamorphism:Metamorphism:Modification of Modification of
Rocks by Rocks by Temperature Temperature and Pressureand Pressure
About MetamorphismAbout Metamorphism•• Changes in heat, pressure, and the chemical environment of rocks can alter Changes in heat, pressure, and the chemical environment of rocks can alter
mineral compositions and crystalline textures, making them metamorphic.mineral compositions and crystalline textures, making them metamorphic.
•• Metamorphic changes occur in the solid state, so there is no melting. Metamorphic changes occur in the solid state, so there is no melting.
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Lecture OutlineLecture Outline1.1. Metamorphism and the Earth systemMetamorphism and the Earth system
2. Causes of metamorphism2. Causes of metamorphism
3. Types of metamorphism3. Types of metamorphism
4. Metamorphic textures4. Metamorphic textures
5. Regional metamorphism and 5. Regional metamorphism and
metamorphic grademetamorphic grade
6. Plate tectonics and metamorphism6. Plate tectonics and metamorphism
11. Metamorphism and the Earth system. Metamorphism and the Earth system
●● driven by Earth’s internal heatdriven by Earth’s internal heat●● closely related to plate tectonicsclosely related to plate tectonics●● releases gasses into atmospherereleases gasses into atmosphere
22. Causes of metamorphism. Causes of metamorphism●● internal heat of internal heat of EarthEarth
temperature increases with depthtemperature increases with depth●● rate = 20º to 60º C per kmrate = 20º to 60º C per km●● at 15 km depth: 450º Cat 15 km depth: 450º C
●● internal pressure of Earthinternal pressure of Earth●● fluid composition inside Earthfluid composition inside Earth
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22. Causes of metamorphism. Causes of metamorphism●● pressure and temperature pressure and temperature increase increase with with depth in all depth in all regionsregions
22. Causes of metamorphism. Causes of metamorphism●● grades grades of of metamorphism (low, intermediate and high) metamorphism (low, intermediate and high)
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22. Causes of metamorphism. Causes of metamorphism●● the role of temperature the role of temperature
●● geothermal gradientgeothermal gradient●● shallow (20º C / km)shallow (20º C / km)●● steep (50º C / kmsteep (50º C / km))
●● the role of pressure (stress)the role of pressure (stress)●● confining pressureconfining pressure●● directed pressuredirected pressure●● rate of increase = 0.3 to 0.4 rate of increase = 0.3 to 0.4 kbarkbar / km/ km●● minerals are minerals are geobarometersgeobarometers
●● the role of fluidsthe role of fluids●● metasomatismmetasomatism●● accelerated chemical reactionsaccelerated chemical reactions
Depth,km
0
35
75
Regional metamorphism Oceanic
crust
Oceaniclithosphere
ShockShockmetamorphismmetamorphism
RegionalRegionalmetamorphismmetamorphism
RegionalRegionalhighhigh--pressurepressuremetamorphismmetamorphism
ContactContactmetamorphismmetamorphism
BurialBurialmetamorphismmetamorphism
Water
SeafloorSeafloormetamorphismmetamorphism
3. Types of metamorphism3. Types of metamorphism
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slatyslaty cleavage planescleavage planes
beddingbeddingplanesplanes
Metamorphism changes Metamorphism changes sedimentary rocks, thus sedimentary rocks, thus forming slaty cleavage planes.forming slaty cleavage planes.
4. Metamorphic textures4. Metamorphic textures
shaleshale
sandstonesandstonelayerslayers
5 cm5 cm
The original beddingThe original beddingcan be seen in the can be seen in the thin sandy layers.thin sandy layers.
Regional metamorphism Regional metamorphism causes cleavage planescauses cleavage planesto develop.to develop.
foliationfoliationplaneplane
originalbedding
44. Metamorphic textures. Metamorphic textures
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MicaMica
PyritePyrite StauroliteStaurolite
QuartzQuartz
FeldsparFeldspar
Foliation is the resultFoliation is the resultof compressive forces.of compressive forces.
Mineral crystals become Mineral crystals become elongated elongated perpendicular to perpendicular to the compressive the compressive force.force.
4. Metamorphic textures4. Metamorphic textures
StauroliteStaurolitecrystalcrystal
MicaMica
Foliated rocks contain platy Foliated rocks contain platy minerals that are aligned along minerals that are aligned along a preferred orientation.a preferred orientation.
Increasing intensity of metamorphismIncreasing intensity of metamorphism
Increasing crystal sizeIncreasing crystal size
Increasing coarseness of foliationIncreasing coarseness of foliation
Low grade Intermediate grade High grade
Diagenesis Low grade Intermediategrade
High grade
Slate Phyllite Schist(abundantmicaceousminerals)
Gneiss(fewer
micaceousminerals)
Migmatite
Slaty cleavage Schistosity Banding Banding
Foliated rocks are classified by the degree of cleavage, schistosity, and banding.
4. Metamorphic textures4. Metamorphic textures
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GranoblasticGranoblastic texturestexturesFoliated textureFoliated texture::Schist with garnet Schist with garnet porphyroporphyro--blastsblasts
4. Metamorphic textures4. Metamorphic textures
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Canada
NY
VT
ME
NH
MA
CT
RI
Isograds
Key: Notmetamorphosed
Chlorite zone
Biotite zone
Garnet zone
Staurolite zone
Sillimanite zone
Lowgrade
Mediumgrade
High grade
IsogradsIsograds can becan beused to plot theused to plot thelevel or degree of level or degree of metamorphism.metamorphism.
● mineral isograds (zones of change)● index minerals reflect pressure and temperature conditions (or define metamorphic zones), ● groups of 2 to 3 index minerals form an isograd
55. Regional . Regional metamorphism and metamorphism and metamorphic grademetamorphic grade
Pres
sure
(Pr
essu
re (k
iloba
rski
loba
rs))
Temperature (Temperature (°°C)C)
Dep
th (k
m)
Dep
th (k
m)
LowGrade
IntermediateGrade
HighGrade
Slate
Phyllite
Schist
Blueschist GneissMigmatite
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Degree of metamorphismDiagenesisGreenschists
Low IntermediateAmphibolites Granulites
High
Chlorite
White mica (mainly muscovite)
Biotite
Garnet
Staurolite
Sillimanite
Kyanite
Albite (sodium plagioclase)
With increasing metamorphicWith increasing metamorphicgrade, mineral compositiongrade, mineral compositionchanges.changes.
Mineral suites defineMineral suites definemetamorphic metamorphic faciesfacies..
Pre
ssu
re (
kil
ob
ars)
Temperature (°C)
Dep
th (
km
)
20
15
10
5
0
0 200 400 600 800 100040
35
30
25
20
15
10
5
0HornfelsHornfels
EclogiteEclogite
Green
schist
Green
schist
Am
ph
ibo
liteA
mp
hib
olite
Gran
ulite
Gran
ulite
13.5
Metamorphic Metamorphic faciesfacies correspondcorrespondto particular combinations ofto particular combinations ofpressure and temperature...pressure and temperature...
… and can be used … and can be used to indicate specific to indicate specific tectonic environments.tectonic environments.
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5. Regional metamorphism 5. Regional metamorphism and metamorphic gradeand metamorphic grade
Low P,Low T
High P,High THigh P,High T
Tectonic transport moves Tectonic transport moves rocks through different rocks through different pressurepressure--temperature temperature zones, …zones, …
…and then transports them…and then transports themback to the shallow crust or back to the shallow crust or the surface.the surface.
●● metamorphism occurs in or nearmetamorphism occurs in or near●● plate interiorsplate interiors●● divergent plate marginsdivergent plate margins●● convergent plate marginsconvergent plate margins●● transform plate transform plate marginsmargins
6. Plate tectonics and metamorphism6. Plate tectonics and metamorphism
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During metamorphism,During metamorphism,a garnet crystal grows,a garnet crystal grows,and its composition and its composition changes.changes.
thin section of garnet gneissthin section of garnet gneiss growth zone in garnetgrowth zone in garnet
Composition of crystalComposition of crystalcan be plotted on thecan be plotted on thePP--T path as it grows.T path as it grows.
66. Plate tectonics and metamorphism. Plate tectonics and metamorphismmetamorphic pressure and temperature pathsmetamorphic pressure and temperature paths
Pres
sure
(kilo
bars
)Pr
essu
re (k
iloba
rs)
Temperature (Temperature (°°C)C)
Dep
th (k
m)
Dep
th (k
m)
LowGrade
IntermediateGrade
HighGrade
The garnet crystal initially grows in a schist The garnet crystal initially grows in a schist but ends up growing in a gneiss.but ends up growing in a gneiss.
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Temperature (°C)
Depth
(km
)
LowGrade
HighGrade
Peak metamorphism
Subduction mélange, low temperature–high pressure metamorphism
Continentalcrust Shelf
sedimentShelfsediment
Deep-oceansedimentDeep-oceansediment
OceaniccrustOceaniccrust
Trench
MélangeophiolitesMélangeophiolites
Progradepath
Peakmetamorphism Retrograde
path
ContinentalcrustContinentalcrust
High temperature–high pressure metamorphism within mountain belts
Deformed andmetamorphosedshallow- and deep-ocean sediments
Deformed andmetamorphosedshallow- and deep-ocean sediments
Continentalcrust
ContinentalcrustContinentalcrust
MultiplethrustsMultiplethrusts
Progradepath
Peakmetamorphism Retrograde
path
Suture
Pre
ssu
re (
kil
ob
ars
)
AmphiboliteAmphiboliteBlueschistBlueschistContact Contact metamorphismmetamorphismEclogiteEclogiteFoliated Foliated rockrockFoliationFoliationGneissGneissGranoblasticGranoblastic rockrockGranuliteGranuliteHighHigh--pressure pressure metamorphismmetamorphismHornfelsHornfelsLowLow--grade metamorphismgrade metamorphismMarbleMarbleMetamorphic Metamorphic faciesfaciesMetamorphic rockMetamorphic rockMetasomatismMetasomatismMigmatiteMigmatite
Key terms and conceptsKey terms and conceptsPhyllitePhyllitePorphyroblastPorphyroblastQuartziteQuartziteRegional Regional metamorphismmetamorphismSchistSchistSeafloor Seafloor metamorphismmetamorphismShock metamorphismShock metamorphismSlateSlateStressStressUltraUltra--high pressure metamorphismhigh pressure metamorphismZeoliteZeolite
