l5 batuan metamorfik
TRANSCRIPT
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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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NEXT LECTURE
MASA GEOLOGI