l5 batuan metamorfik

8/11/2019 L5 Batuan metamorfik

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Metamorfisme dan

batuan metamorfik


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PREEXISTING

ROCKS

BATUAN

METAMORFIKT, P, CHEMICAL

FLUIDS

METAMORFISME

CONTACT

REGIONAL/

DYNAMIC

CHANGES

TEXTURE

MINERALOGY

LINEATION

FOLIATION

NONFOLIATED

HOW

WHERE

HOW

WHERE

JENIS BATUAN

& CIRI KEJU-

RUTERAAN

JENIS


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Metamorphism means

"changed form (berubahbentuk)


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Kitar batuan (Rock cycle)


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CYCLE


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Batuan Metamorfik terjadihasil drpd perubahan suhu,

tekanan dan bendalir kimia

Agents of Metamorphism

Changes occur because of:

Heat

Pressure

Chemical fluids


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Perubahan suhu:

Geothermal gradient

Temperature increases with depth ata rate of 20 - 30 degrees C per km inthe crust.

Ultimate source of the heat?Radioactive decay. Increase oftemperature and pressure with depthcausesRegional Metamorphism

Metamorfisme Rantau)Heat may come from large bodies ofmolten rock rising under a wide

geographic area.


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Metamorfisme sentuh

Intrusions of hot magma can

bakerocks as it intrudes them.

Lava flows can also bake rockson the ground surface. Lava or

magma in contact with other

rock causes ContactMetamorphism.

Hornfelsis a common contact

metamorphic rock.


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CONTACT


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Contact metamorphism


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Contact

metamorphismContact metamorphism

along a narrow (approx. 1

meter wide) diabase dike in

the Deep River Basin ofNorth Carolina. Diabase

weathers tan. Contact

metamorphic aureole rocks

(hornfels) are gray. Hostrocks are red siltstones


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REGIONAL


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Continental collision


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SUBDUCTION


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3 Chemical Fluids

In some metamorphic settings, newmaterials are introduced by the action ofhydrothermal solutions(hot water withdissolved ions). Many metallic ore depositsform in this way.

Hydrothermal solutions associated with

magma bodies Black smokers- Sea water percolates

through newly formed oceanic crust,dissolving out metallic sulfide minerals. Thehot sea water rises along fractures and

pours from vents in the seafloor as blackclouds of dark mineral-rich water. Sulfideminerals (such as pyrite, sphalerite, andgalena) and copper precipitate when the hotwater comes in contact with cold sea water


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HYDROTHERMAL


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How do rocks change?

Metamorphism causes changes in:

1 Texture (definition: shape, sizeand orientation of mineral

grains in the rocks)

2 Mineralogy (chemicalcomposition)


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STRESS


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FOLIATION


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FOLIATION


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STRESS

FOLIATED


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FOLIATED


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Foliasi


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Recrystallization

Growth of new crystals. No changesin overall chemistry. New crystalsgrow from the minerals alreadypresent. A preferred orientation of

minerals commonly develops underapplied pressure. Platy or sheet-likeminerals such as muscovite andbiotite become orientedperpendicular to the direction offorce. This preferred orientation iscalled foliation.


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Metamorphic

Textures

Foliation is a broad term referring to thealignment of sheet-like minerals. Types offoliation:

Schistosity- alignment of large mica flakes, as

in a mica schistderived from themetamorphism of shale.

Slaty cleavage- alignment of very fine-grainedmicas, as in a slatederived from themetamorphism of shale.

Phyllitic structure- alignment of fine-grainedmicas, as in aphyllite.

Gneissic banding- segregation of light and darkminerals into distinct layers in the rock, as in a

gneiss


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Lineation

refers to the alignment of

elongated, rod-like minerals

such as amphibole, pyroxene,tourmaline, kyanite, etc.

Lineation is a texture commonly

seen in the metamorphic rockamphibolitederived from the

metamorphism of basalt


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Non-foliatedor granular

metamorphic rocks

are those which are composedof equidimensional grains such

as quartz or calcite. There is nopreferred orientation. Thegrains form a mosaic.Examples: quartzitederived

from the metamorphism ofquartz sandstone, and marblederived from the metamorphismof limestone or dolostone.


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Note: Not all quartzites andmarbles are pure. Some containimpurities that were originallymudinterlayered with or mixed

with the original quartz sand orlime mud. These clay impuritiesmetamorphose to layers ofmicas or other minerals, which

may give marble (in particular) abanded, gneissic appearance, orwhich may give a slight foliationto some quartzites


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Foliated metamorphic

rocks

As shale is subjected to

increasing grade of

metamorphism (increasingtemperatures and pressures), it

undergoes successive changes

in texture associated with anincrease in the size of the mica

grains


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Slate

very fine grained rock.Resembles shale. Has slaty

cleavage which may be at an

angle to the original bedding.Relict bedding may be seen on

cleavage planes. Often dark gray

in color. "Rings" when you strike

it. (Unlike shale, which makes adull sound. Temperature about

200 degrees C; Depth of burial

about 10 km.


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slate


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phyllite


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Schist

metamorphic rock containing abundant

obvious micas, several millimeters

across. Several types of schist may be

recognized, based on minerals whichmay be present:

mica schist

garnet schist

chlorite schist

kyanite schist

talc schist


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schist


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Gneiss

(pronounced "nice") - a banded

or striped rock with alternating

layers of dark and lightminerals. The dark layers

commonly contain biotite, and

the light layers commonlycontain quartz and feldspar


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gneiss


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gneiss


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Migmatite

a very high grade metamorphic

rock that has been subjected to

such high temperatures that it has

partially melted. It is intermediate

between the metamorphic and the

igneous rocks. Look for swirled

banding. The light colored

minerals have undergone melting

and flow. The dark colored

minerals have been contorted by

flow. Example - the Lithonia

Gneiss in the area southeast of

Atlanta


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migmatite


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non-foliated and weakly foliated)

metamorphic rocks

Marble- fizzes in acid because

its dominant minerals is calcite

(or dolomite). The parent rockis limestone (or dolostone).

( )


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Marmar (Marble)


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Quartzite/kuarzit

interlocking grains of quartz.

Scratches glass. The rock

fractures through the grains(rather than between the grains

as it does in sandstone). The

parent rock is quartz sandstoneHardest rock known

UCS


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quartzite


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Others

Metagraywacke-

metamorphosed graywacke or"dirty sandstone".

Metaconglomerateand

stretched pebble

metaconglomerate- the parent

rock is conglomerate. The clasts

are fairly easily recognized. Maybe more difficult to recognize if

the clasts have been stretched


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Hornfels

A fine-grained, tough, dense,

hard, massive rock. Usually (but

not always) dark in color. Finergrained than basalt, which it

may superficially resemble. This

rock forms throughcontactmetamorphism. The parent rock

is commonly siltstone or basalt,

but may be other types of rock


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Serpentinite

A dark green, dense, tough,massive, hard rack. May contain

veins of asbestos. The parent

rock is peridotite, an ultramaficrock

ultramafic: lack/low amount of

SiO2, Fe, Mg (bandingkan dgnjadual pengelasan batuan

igneus)


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serpentine


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Soapstone

(sometimes called steatite) - a soft,easily carved rock with a slippery

feel because it contains talc and

chlorite. The parent rock isperidotite (ultramafic), probably

with more water associated with it

than in the formation ofserpentinite. Example - Soapstone

Ridge southeast of Atlanta


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Metabasalt

(sometimes called greenstoneif

massive and green, or

greenschistif foliated andgreen) - the green color comes

from chlorite (soft and bluish

green) and epidote (pea green).The parent rock is basalt. The

grade of metamorphism is LOW


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Amphibolite

Abundant amphibole is present;

may be lineated. Usually black.

The parent rock is basalt. Thegrade of metamorphism is

HIGH. Has been subjected to

higher temperatures andpressures than metabasalt,

greenstone, or greenschist.


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Mylonite

A dynamic metamorphic rock

which forms along fault zones

l it


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mylonite

Mylonite along the Linville Falls Fault, Linville Falls,

NC. Relatively undeformed conglomeratic quartzite

lies above the layered mylonite zone


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Mineral changes in

metamorphic rocks

Recrystallization- rearrangement ofcrystal structure of existing minerals.Commonly many small crystals mergeto form larger crystals, such as the

clay in shale becoming micas inslate, phyllite, and schist. Note thechemical compositions of clay andmuscovite.

Also, fine-grained calcite in limestonerecrystallizes to the coarse-grainedcalcite mosaic in marble


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Formation of new minerals

there are a number of

metamorphic minerals whichform during metamorphism andare found exclusively (or almost

exclusively) in metamorphicrocks:

Garnet - dark reddodecahedrons (12 sides)

Staurolite - brown lozenge-shaped minerals, commonlytwinned to form "fairy crosses".

State mineral of Georgia

garnet


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garnetKegunaan?


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Kyanite

sky blue bladed minerals with

differential hardness. Scratch

lengthwise with a knife or nail,but not sideways


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kyanite

Chlorite - dark bluish green, soft. Fe, Mg


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Chlorite dark bluish green, soft. Fe, Mg

Talc- white or pale green and soft.

Graphite- metamorphosed carbon

Tourmaline- commonly black. Formselongated crystals with a roundedtriangular cross-section. Can see atStone Mountain.

Asbestos- fibrous mineral. Commonlylight greenish. Occurs in veins (seemsto fill a crack) with the fibers orientedperpendicular to the edged of the vein.Associated with lung diseases.

Mesothelioma and asbestosis. Found inserpentinite. "Serpent rock" name dueto snake-like veins of asbestos.

Micas- muscovite (silvery), biotite(darkbrown), phlogopite(light brown)


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Batuan metamorfik boleh digunakansebagai tanda aras suhu dan tekanan

dalam bumi

In regional metamorphic terranes, the

temperature and pressure regime isindicated by the distribution ofmetamorphic minerals across a large area.Low metamorphic grade(low temperaturesand pressures) - about 200 degrees C

Slate and phyllite chlorite

muscovite

biotite

Metamorphic index minerals


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Intermediate metamorphic grade

Schist

garnet

staurolite

KOMPOSISI KIMIA?


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High metamorphic grade- 800

degrees C (verging on melting)Gneiss and migmatite

sillimanite

Know which minerals are themetamorphic index minerals.

Know which ones are

characteristic of low,intermediate, and high

metamorphic grades

FACIES GRADE


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FACIES GRADE

FACIES


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FACIES


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Mi l t d t d


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Mineral yg terdapat pada

zon metamorfik

REGIONAL


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foliation

Slate schist gneiss texture

Gran lar te t re as in


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Granular texture as in

quartzite

Rumus


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Changes that occur in the

transformation to becomemetamorphic rocks


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ENGINEERINGPROPERTIES

1. POROSITY

2. KEKUATAN EKAPAKSI (UCS)

3. PERMEABILITY4. ABRASIVENESS


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HOW


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PREEXISTING

ROCKS

BATUANMETAMORFIK

T, P, CHEMICAL

FLUIDS

METAMORFISME

CONTACT

REGIONAL/

DYNAMIC

CHANGES

TEXTURE

MINERALOGY

LINEATION

FOLIATION

NONFOLIATED

WHERE

HOW

WHERE

JENIS BATUAN& CIRI KEJU-

RUTERAAN

JENIS

PHASE DIAGRAM FOR WATER


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PHASE DIAGRAM FOR WATER


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l5 batuan metamorfik

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