modul 8 - metamorphic rocks

7/28/2019 Modul 8 - Metamorphic Rocks

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Metamorphic RocksMetamorphic Rocks


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METAMORPHIC ROCKSMETAMORPHIC ROCKS

Metamorphic rocks areMetamorphic rocks are changed rockschanged rocks TheThe protolithprotolith (the(the parent rockparent rock ) is the) is the

preexisting rock from which thepreexisting rock from which themetamorphic rock was formedmetamorphic rock was formed

They areThey are formed in the solid stateformed in the solid state inin

response to the followingresponse to the following principalprincipalagents of metamorphismagents of metamorphism ::

Change inChange in pressurepressure Change inChange in temperaturetemperature

Change inChange in pressurepressure andand temperaturetemperature


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Formation of Metamorphic RocksFormation of Metamorphic Rocks

Metamorphisme


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METAMORPHIC ROCKSMETAMORPHIC ROCKS

Metamorphism may cause a change in a rockMetamorphism may cause a change in a rock s:s:

Structure/TextureStructure/Texture

Mineral assemblageMineral assemblage Composition (slightly)Composition (slightly)

All of the aboveAll of the above


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Factors That Control the Characteristics ofFactors That Control the Characteristics ofMetamorphic RocksMetamorphic Rocks

1.1. ProtolithProtolith CompositionComposition

2.2. PressurePressure

3.3. TemperatureTemperature

4.4. TimeTime

C C f


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1.1. ProtolithProtolith CompositionComposition

MaficMafic protolithsprotoliths (basalt,(basalt, diabasediabase, and, and gabbrogabbro))

yield a dark charcoal grayyield a dark charcoal gray maficmafic metamorphicmetamorphic

rock calledrock called amphiboliteamphibolite

FelsicFelsic protolithsprotoliths (granite,(granite, rhyoliterhyolite, mudstone,, mudstone,

sandstone, conglomerate,sandstone, conglomerate, brecciabreccia) yield light) yield light

colored tan, silver, light to medium gray, etc.colored tan, silver, light to medium gray, etc.

felsicfelsic metamorphic rocksmetamorphic rocks

F Th C l h Ch i i fF t Th t C t l th Ch t i ti f


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2. Pressure (stress)

Increasing pressure flattens grains, crushesgrains (reduces size), causes shearing

Confining pressure, associated with depth ofburial, is equal in all directions

Differential pressure is not equal in all

directions Produces foliation (parallel alignment of

grains)

Pure shear = compression, flattens grains Simple shear = skewing, stretches grains,

produces lineation, aligns elongate grains

in direction of transport

F t Th t C t l th Ch t i ti fF t Th t C t l th Ch t i ti f


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Confining PressureConfining Pressure

Pressure is equal inPressure is equal in

all directionsall directions

F t Th t C t l th Ch t i ti fF t Th t C t l th Ch t i ti f


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Differential PressureDifferential Pressure Differential pressureDifferential pressure

IsIs notnot equal in all directionsequal in all directions

Leads toLeads to formation of foliationformation of foliation by eitherby either

Pure shear (flattening)Pure shear (flattening)

Simple shear (skewing)Simple shear (skewing)

Pure shear (flattening)Pure shear (flattening) Simple shear (skewing)Simple shear (skewing)

F t Th t C t l th Ch t i ti fFactors That Control the Characteristics of


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Type of foliationType of foliation

Slaty Cleavage Alignment of small micaflakes

Schistosity Alignment of large mica

flakes

Gneissic Banding segregation of felsic

and mafic minerals into alternating lightand dark bands

Factors That Control the Characteristics ofFactors That Control the Characteristics of


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Bedding is perpendicular to cleavage

at the top and bottom of the fold

Foliation: Development of Slaty CleavageFoliation: Development of Slaty Cleavage




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Foliation: Development of SchistosityFoliation: Development of Schistosity

http://www.tulane.edu/~sanelson/geol212/contactmeta.htm



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Foliation: Formation of Gneissic BandingFoliation: Formation of Gneissic Banding



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3.3. TemperatureTemperature

Increasing temperatureIncreasing temperature causes increasedcauses increased

movement of ions which in turn causesmovement of ions which in turn causes Mineral grains to grow largerMineral grains to grow larger

New minerals to form moving up BowensNew minerals to form moving up Bowens

Reaction SeriesReaction Series Minerals toMinerals to recrystallizerecrystallize

Decreasing temperatureDecreasing temperature causes new mineralscauses new minerals

to form moving down Bowens Reaction seriesto form moving down Bowens Reaction series The upper limit on T for metamorphism isThe upper limit on T for metamorphism is

partial meltingpartial melting


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Tempe

rature&

pressuredecreases

Temperature&pressureincreases

Olivine

Pyroxene

Amphibole

Biotite

Ca-rich

Na-rich

Ca-Na-rich

Na-Ca-rich

Quartz

Musc

ovite

K-feldspar P

lagi

oc

lase

fe

lds

par

BOWENS REACTION SERIES

1200C

700C

High

Intermediate

Low

The Effect of Temperature Changes on Composition and MetamorphisThe Effect of Temperature Changes on Composition and Metamorphismm

MAFIC

INTM

FELSIC



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4. Time Metamorphic reactions and textural changes

require mill ions of years to occur


Index Minerals of Metamorphic RocksIndex Minerals of Metamorphic Rocks


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Index Minerals of Metamorphic RocksIndex Minerals of Metamorphic RocksIndex MineralsIndex Minerals

Chlorite Biotite Almandite (garnet) Staurolite

Andalusite Kyanite Sillimanite

Not specificNot specific Quartz Plagioclase

Orthoclase Biotite Muscovite Hornblende Calcite Dolomite

Sillim

anite

Biotite

Chlo

rite

And

alusite

Ky

anite

Alm

a

ndite

(Garn

et)

Staurolite

MetamorphicMetamorphic FaciesFacies


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MetamorphicMetamorphic FaciesFacies

o

Classification of Metamorphic RocksClassification of Metamorphic Rocks


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1. Regional metamorphic rocks

Form in response to increased temperatureand directed pressure along plate boundaries

Are foliated

Were sheared by pure shear or simple shear

2. Contact metamorphic rocks

Form in response to contact with magma athigh T and /or high confining P

Found adjacent to igneous intrusions

Are usually unfoliated

Where do the metamorphic rocks form?Where do the metamorphic rocks form?


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Where do the metamorphic rocks form?Where do the metamorphic rocks form?



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Formation ofFormation ofRegional MetamorphicRegional Metamorphic

RocksRocks


Formation ofFormation of

Contact MetamorphicContact Metamorphic

RocksRocks



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Contact metamorphic rocksRegional metamorphic rocks




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C ass ca o o e a o p c oc sC ass ca o o e a o p c oc sFormation of Contact Metamorphic RocksFormation of Contact Metamorphic Rocks

ProtolithProtolith and Metamorphic Rocksand Metamorphic Rocks


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pp


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Perubahan TexturFoliasiSlaty CleavageSekistositasCompositional Banding

FOLIASI


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FOLIASI

YATIDAK

UKURAN BUTIR

SangatHalus Halus Sedang Kasar

Sekis GenisKuarsit

Migmatik

Filit MilonitPilonit

Eklogit SlateAmfibolit GranulitHornfels Marmer

KasarSedang-halus

UKURAN BUTIR

Mineral Utama?Keras?

YA Amfibol Kalsit Kuarsa GarnetPiroksen

FeldsparPiroksen

Keras?

PucatKataklstik

Kehijauan

Schistosity GneissoreSlaty Cleavage

Types of Metamorphic RocksTypes of Metamorphic Rocks


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Are formed by differential pressure (pure shear, simple shear)

SlateDull, microscopic grains, strong slaty cleavage, anycolor, mudstone protolith

Phyllite

Shiny, strongly micaceous with microscopic grains,strong schistosity, cleavage, can be mafic or felsic, anyrock-type protolith

Schist

Shiny, strongly micaceous, fine to medium grained,strong schistosity, cleavage, any color, any rock-typeprotolith

Gneiss

Dull, weakly micaceous, fine to coarse grained, banded,

weak cleavage, any rock-type protolith, but most oftensheared coarse grained protolith such as granite,conglomerate, breccia

Migmatite

Dull, weakly micaceous, fine to coarse grained, foldedbanded texture, weak cleavage, almost melted, any rock-type protolith

A. Foliated Metamorphic RocksA. Foliated Metamorphic Rocks

yp pyp p



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Protolith:Protolith: Fine grained rock likeFine grained rock likeshale, mudstone, or siltstoneshale, mudstone, or siltstone

SlateSlate

Appearance:Appearance: Dull, microscopicDull, microscopicgrains, strong slaty cleavage,grains, strong slaty cleavage,

any colorany color

yp p


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Slate (Batusabak)



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PhyllitePhyllite

Appearance:Appearance: Shiny, stronglyShiny, stronglymicaceousmicaceous withwith microscopicmicroscopic

grainsgrains , has strong schistose, has strong schistose

cleavage, can be felsiccleavage, can be felsic

(muscovite(muscovite--rich, silvery) orrich, silvery) orMafic (Mafic (biotitebiotite--rich, shinyrich, shiny

medium to dark gray)medium to dark gray)

Protolith:Protolith: Can be any rockCan be any rock--typetype


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FILIT MIKA


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SEKIS KLORITOID



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SchistSchist

Appearance:Appearance: Shiny, stronglyShiny, stronglymicaceousmicaceous, fine to medium grained, fine to medium grained

has strong schistose cleavage,has strong schistose cleavage,

can be felsic (muscovitecan be felsic (muscovite--rich,rich,

silvery) or mafic (silvery) or mafic (biotitebiotite--rich,rich,shiny medium to dark gray)shiny medium to dark gray)



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SEKIS


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SEKIS


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SEKIS GARNET-MIKA


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MILONIT



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GneissGneiss

Protolith:Protolith: Can be any rockCan be any rock--type,type, but

most often formed from a sheared

coarse grained protolith such asgranite, conglomerate, breccia

Appearance:Appearance: Dull, weakly micaceous,

fine to coarse grained, banded, weak

cleavage


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GENIS-MIGMATIT


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GENES


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GENIS



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MigmatiteMigmatite


Appearance:Appearance: Dull, weakly micaceous,

fine to coarse grained, folded banded

texture, weak cleavage, almost melted,

a folded gneiss


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MIGMATIT

B Special Types of Metamorphic RocksB Special Types of Metamorphic Rocks



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B. Special Types of Metamorphic RocksB. Special Types of Metamorphic Rocks

May be foliated or unfoliated Quartzite

Metamorphosed sandstone

Harder than marble Will not fizz (release CO2) in the presence of acid
http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/photogallery/images/Quartzite%202_jpg.jpg


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METAPSAMIT(META BATUPASIR)

B. Special Types of Metamorphic RocksB. Special Types of Metamorphic Rocks



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B. Special Types of Metamorphic Rocksp yp p

Marble

Metamorphosed limestone

Contains calcium carbonate

Will f izz (release CO2) in the presence of acid

Softer than quartzite

May be foliated or unfoliated
http://www.pitt.edu/~cejones/GeoImages/6MetamorphicRocks/Marble/MarbleWhite.jpg


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MARMER


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MARMER

B. Special Types of Metamorphic RocksB. Special Types of Metamorphic RocksTypes of Metamorphic RocksTypes of Metamorphic Rocks


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p yp pp yp p

AmphiboliteMay be foliated or unfoliated

Dull black, fine to coarse grained, weak cleavage if

sheared (gneissic) Metamorphosed gabbro, basalt, or diorite

Dark rock composed mostly of amphibole and Ca-Na plagioclase, may be

either foliated or unfoliated, often with large (visible) elongated crystals ofamphibole
http://www.smccd.net/accounts/hand/geology101/metamorphic/images/amphibolite2.jpghttp://www.smccd.net/accounts/hand/geology101/metamorphic/images/amphibolite2.jpghttp://www.smccd.net/accounts/hand/geology101/metamorphic/images/amphibolite2.jpghttp://www.smccd.net/accounts/hand/geology101/metamorphic/images/amphibolite2.jpghttp://www.smccd.net/accounts/hand/geology101/metamorphic/images/amphibolite1.jpg


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SKARN


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EKLOGIT


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EKLOGIT

modul 8 - metamorphic rocks

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