M E T A M O R F O S A ……. adalah sebuah proses. asal kata : META .......UBAH. dan MORF ......... BENTUK PROSES METAMORFOSA ADALAH PROSES P E R U B A H A N B E N T U K.

T &

P

T&P

T&

P

T &

P

BATUAN M E T A M O R F

MIGMATITES: metamorphic or igneous rocks?

PROSES METAMORFOSA BERLANGSUNG DALAM KEADAAN PADAT PERUBAHAN SISTIM KRISTAL (KARENA ITU DISEBUT

SEBAGAI PROSES REKRISTALISASI ) DAN DIDALAM PROSES TERSEBUT TIDAK TERJADI PENAMBAHAN MAUPUN

PENGURANGAN UNSUR , PERISTIWA INI DISEBUT JUGA PROSES ISOKIMIA.

REKRISTALISASI

ISOKIMIA

METAMORFOSA

PRESSURE also increases with depth.Pressure on rocks (comes from all directions) causes the spaces between minerals to close.Result is a more compact rock with greater density.

When temperature and pressure both increase, this causes rock to flow rather than fracture.Mineral grains tend to flatten rather than elongate.

AGEN METAMORFOSAAGEN METAMORFOSA.. T dan PT dan Pdarimana T dan P datang atau berasal ?darimana T dan P datang atau berasal ?

HEAT comes primarily from two sources: Magma.

Magma “bakes” any rocks that come in contact with it. Changes in temperature with increased depth. The change in temperature in the upper crust is 20oC to 30oC per kilometer.

At 8 kilometer, clay minerals are exposed to 150oC – 200oC which makes the minerals unstable.

LIMITS OF METAMORPHISMbatas-batas peristiwa metamorfosaCORREN (1950) menyatakaan bahwa, semua perubahan yang terjadi

(apakah itu proses pembentukan batuan sedimen ataupun proses metamorfosa), tidak ada perubahan yang bersifat mendadak; yang ada adalah suatu sekuen menerus. Proses DIAGENESA yang berlangsung pada pembentukan batuan sedimen akan berhenti bila semua rongga (antar kepingan) yang saling berhubungan sudah tertutup oleh proses kimiawi ataupun fisika, bila perubahan berkelanjutan maka akan diteruskan dengan proses metamorfosa atau pada zona ini proses metamorfosa dimulai.

Ada mineral yang dapat ditemui baik pada batuan sedimen maupun pada batuan metamorf, seperti mineral feldspar, klorit, kuarsa; tetapi ada juga mineral yang tidak stabil pada proses diagenesa, sehingga hanya dapat ditemui pada batuan metamorf saja. Glaucophane, epidote, lauminite, paragonite, lawsonite, pyrophylite,

TEMPERATUR : MERUPAKAN FAKTOR UTAMA DALAM PROSES METAMORFOSA.

• Peningkatan temperatur membuka

penghalang (kinetic barrier)

rekristalisasi; ...... dan butiran kecil melebur kedalam butiran lebih

besar.• Mendorong reaksi

yang memakan mineral tidak stabil

dan menghasilkan mineral baru yang lebih stabil

• Batas terendah, – batas pada proses diagenesa. Batas ini tidak pasti, metmorfosa berlangsung pada sekitar 100-150o C.

• Batas temperatur tinggi – diatas kisaran pelelehan dari solid ke likuid.

TEKANAN : T/P TINGGI DIDAERAH AKTIP PLUTONIK ATAU “DAERAH RIFTING”, T/P RENDAH DI DAERAH SUBDUKSI.

Lithostatic pressure is uniform stress (hydrostatic)Deviatoric stress = unequal pressure in different directionsDeviatoric stress can be resolved into three mutually

perpendicular stress (s) components:

s1 is the maximum principal stress s2 is an intermediate principal stress s3 is the minimum principal stress

In hydrostatic situations all three are equal.

• Stress is an applied force acting on a rock (over a particular cross-sectional area).

• Strain is the response of the rock to an applied stress (= yielding or deformation)

• Deviatoric stress affects the textures and structures, but not the equilibrium mineral assemblage.

Strain energy may overcome kinetic barriers to reactions.

• Deviatoric stresses come in three principal types: Tension, Compression, Shear.

Deviatoric stresses come in three principal types: Tension, Compression, Shear.Tension: 3 is negative, and the resulting strain is extension, orpulling apart original shape

strain ellipsoid

Compression: 1 is dominant, folding or

more homogenous flattening

Shear motion occurs along planes at an angle to 1

• Foliation is a common result, which allows us to estimate the orientation of 1.

1 > 2 = 3 foliation and no lineation 1 = 2 > 3 lineation and no foliation 1 > 2 > 3 both foliation and lineation

High Strain Rocks

PERISTIWA YANG BERLANGSUNG :1.SOLID – SOLI REACTION POLIMORF (kyanite, sillimatnite, andalusite).2. DEHIDRATION Al2 Si4 O10 (OH)2 Al2 Si O5 + 3 SiO2 + H2O.3. DECARBINATION CaCO3 + SiO2 CaSiO3 + CO2 .4. OXIDATION AND – REDUCTION 6 Fe2O3 4 Fe3O4 + O2

PROSES PEMBENTUKAN MINERAL.1. DALAM KEADAAN PADAT.2.DALAM SISTIM TERTUTUP.3.TIDAK ADA PENAMBAHAN ATAUPUN PENGURANGAN UNSUR DALAM SISTIM TERSEBUT; YANG TERJADI HANYALAH PERTUKARAN UNSUR ANTAR MINERAL YANG BERSENTUHAN.

DALAM BATUGAMPING HADIR DOLOMIT CaMg(CO3)2 DAN KUARSA SiO2

1. 2CaMg(CO3)2 + 4SiO2 + H2O ↔ Mg2 Si4 O10 (OH)2 + 2CaCO3 +4CO2 dolomit kuarsa talk kalsit

2. 5CaMg(CO3)2 + 8SiO2 + H2O ↔ Ca2Mg5 (Si4 O11)(OH)2 + 3 CaCO3 +7CO2 dolomit kuarsa tremolit kalsit

3. Ca2Mg5 (Si4 O11)(OH)2 + 3 CaCO3+2SiO2 ↔ 5CaMg(SiO3)2 +3CO2 H2O tremolit diopsid 4. Ca2Mg5 (Si4 O11)(OH)2 + 11CaMg(SiO3)2 ↔ Mg2(SiO4) + 13 CaCO3 +9CO2 +H2O tremolit dolomit fosterite 5. Kuarsa + kalsit ↔ wollastonit

CONTOH PROSES PERUBAHAN MINERAL LAMA KE MINERAL BARU:

TEKSTUR BATUAN METAMORF

P E N A M A A N T E K S T U R

TEKSTUR YANG TERBENTUK PADA PROSES METAMORFOSA HASIL PROSES REKRISTALISASI

PADA SAAT METAMORFOSA …… DI BERI AKHIRAN

“- BLAST” ATAU “ – BLASTIC” .

“- BLAST” atau “ – BLASTIC” .

TEKSTUR YANG TERSISA DARI BATUAN ASAL YANG MASIH

NAMPAK ADA PADA BATUAN METAMORF, SEBAGAI PALIMSEST

ATAU “RELICT TEXTURE” , …….. DIBERI AWALAN “BLASTO” .

“BLASTO”

1. KESEMPURNAAN BENTUK KRISTAL ATAU KRISTALOBASTIK (individual): IDIOBLASTIC BENTUK KRISTAL SEMPURNA. XENOBLASTIC BENTUK KRISTAL TIDAK SEMPURNA.

2. KESERAGAMAN UKURAN KRISTAL: ISOGRANULAR, ANEQUIGRANULAR ……….. PORPHYROBLAST.

2. HUBUNGAN ANTAR BUTIR ……………. Fabric. A. TANPA ORIENTASI. B. MENGIKUTI BENTUK MINERAL. C. CAMPURAN ANTARA A DAN B. D. LAIN LAIN.…… LENIATION, FOLIATED DAN NON FOLIATED.

T E K S T U R D A S A R bentuk , ukuran, dan pengaturan butir

HETEROGONAL

A. T A N P A O R I E N T A S I

PORPHYROBLASTIC

B. TERGANTUNG DARI BENTUK MINERAL

HUBUNGAN ANTAR BUTIR

ISOGRANULAR

POLYGONAL MOZAIC

LEPIDOBLASTIC NEMATOBLASTIC

GRANO- LEPIDOBLASTI GRANO- NEMATOBLASTIC GRANO PORPHYROBLASTIC

SHAFE ROSETE NODULAR

CAMPURAN A DAN B

C. LAIN LAIN.

AUGEN VESICULAR CORONATIC

B. TANPA FOLIASI :1.CATACLASTIC TEXTURE.

2.PROTOCLASTIC TEXTURE.

T E K S T U R U M U M A. FOLIATED ROCKS :1. PROTOMYLONITIC

2. AUGEN MYLONITIC.

3. ULTRAMYLON ITIC.

4. BLASTOMYLONITIC

FOLIATION: AND PLANAR FABRIC ELEMENT.LINEATION: ANY LINEAR FABRIC ELEMENTS.

they have no genetic connotations some high-strain rocks may be foliated, but they are treated separately

CLEAVAGE.• Traditionally: the property of a rock to split along a regular set of sub-parallel, closely-

spaced planes. • A more general concept adopted by some geologists is to consider cleavage to be any type of foliation in which the aligned platy phyllosilicates are too fine grained to see individually

with the unaided eye.

SCHISTOSITY

SLATE

PHYLLITE

FOLIATION

LINEATION

a. susunan butir elongated.b.susunan prismatic grain.c.susunan platy grains.d.susunan s-surface.e.susunan perpotongan bidang

M I N E R A L P A R A G E N E S A

dan

F A S I E S M E T A M O R F I K

KUMPULAN MINERAL DALAM BATUAN METAMORF , YAITU (a1,a2,a3,....an) DISEBUT SEBAGAI M I N E R A L P A R A G E N E S A. adalah sekumpulan mineral pembentuk batuan metamorfosa yang terbentuk pada kondisi (T & P) metamorfosa tertentu.

M I N E R A L P A R A G E N E S A.

X1 a1, a2, a3

T1,P1

Y2 a10,a11, a12

X2a4, a5, a6

Y1a7, a8, a9

T2,P2T1,P1

T2,P2 A1m1m2 m3

A2m4m5m6

BATUAN ASAL

BATUAN METAMORF

BATUAN METAMORF

F A S I E S M E T A M O R F O S AMETAMORPHIC FACIES DESIGNATED A GROUP OF ROCKS CHARACTERIZED BY A DEFINITE SET OF MINERALS UNDER PARTUCALLY METAMORPHIC CONDITION.

Every metamorphic facies has some index minerals by which it can be recognized. That does not mean these minerals will necessarily be visible with the naked eye, or even exist in the rock; when the rock did not have the right chemical composition they will not grow.

Very typical index minerals are the polymorphs of aluminosilicate (Al2SiO5, all are nesosilicates). Andalusite is stable at low pressure, kyanite is stable at high pressure but relatively low temperature and sillimanite is stable at high temperature.

FASIES METAMORFOSA, ESKOLA, 1939

ADA 8 (DELAPAN) FASIES METAMORFOSA

A. EMPAT FASIES UTAMA : I. TERDIRI DARI : 1. GREENSCHIST FACIES. Greenschist 2. EPIDOTE – AMPHIBOLITE FACIES. BARROVIAN ZONE ( progresive changes) 3. AMPHIBOLITE FACIES. Amphibolite II. 4. GRANULITE FACIES. FASIES TEMPERATUR TINGGI,

PROGRESIVE CHANGES MIYASHIRO). Granulite

B. FACIES METAMORPHIC ESKOLA, (1939). III. GLAUCOPHANE SCHIST FACIES/BLEUSCHIST FACIES. Glaucophane - Lawsonite Schist or Blueschist

MENANDAI P TINGGI

IV. ECLOGITE FACIES. Eclogite

C. V. PYROXENE – HORNFELS FACIES. FACIES PADA CONTAC METASOMATISM ( P RENDAH). VI. SANIDINITE FACIES.

D. VII. PREHNITE – POKPELLYETE FACIES. Prehnite - Pumpellyite FASIES DALAM “BURIAL METORPHISM”. VIII. ZEOLITE FACIES. Zeolite Facies

The assemblages listed above are mainly for mafic (Metabasite) lithologies. Boundaries between individual facies are not sharp, marked by reactions which occur over a P-T range depending on composition.

4. Greenschist 1.Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks 2.pyrophyllite in pelitic rocks

5. Amphibolite 1.Hornblende + Plagioclase (An > 20) 2.Kyanite (Al2SiO5) in pelites

6. Granulite1.lower crustal lithology 2.cpx + opx + plag + Fe - Mg garnet

7. Eclogite 1.lower crust or upper mantle lithology. 2.Feldspar-free assemblages, with jadiete-rich cpx + pyrope (Mg-rich garnet).

1. Zeolite Facies 1. Zeolites are groups of white to colourless hydrous alumina silicates, analogous in composition to feldspars. 2.Laumontite, heulandite and analcine are common, the assemblage Quartz + Laumontite + Chlorite is diagnostic. 3. Jadiete (NaAlSi2O6) + Qtz + Aragonite

2. Prehnite - Pumpellyite 1.Prehnite +/- Pumpellyite + Quartz is typical. 2.Prehnite - Ca2Al2Si3O10(OH)2 Pumpellyite - Ca2MgAl2(SiO4)(Si2O7)(OH)2H2O

3. Glaucophane - Lawsonite Schist or Blueschist1.High P Low T 2.Glaucophane (Na2MgAl2Si8O22(OH)2) (alkali-rich amphibole) + Lawsonite (CaAl2Si2O7(OH)2H2O) are characteristic also

Mineralogical characteristics of the metamorphic facies

D A S A R K L A S I F I K A S I :1. DASAR TEKSTUR. 2. BERDASARKAN KEJADIAN DAN TEMPAT KEJADIAN.3. DASAR TEMPERATUR DAN TEKANAN.4. DASAR KOMPOSISI BATUAN ASAL.

1 .REGIONAL ATAU OROGENIC METAMORPHIC ROCKS.2. OCEAN FLOOR METAMORPHIC ROCKS.3. CONTACT METAMORPHIC ROCKS.4. CATACLASTIC METAMORPHIC ROKS

1. LOW GRADE METAMORPHIC ROCKS.2. MEDIUM GARDE METAMORPHIC ROKS.3. HIGH GRADE METMORPHC ROCKS.

1. BERASAL DARI PELITIC (ALLUMINOUS ) SEDIMENT :CLAY, SAHLES, MUDSTONE).

2. BERASAL DARI QUARTZO-FELDSPATHOID ROCKS (BATUAN BEKU ASAM).

3. BERASAL DARI CALCAREOUS SEDIMENT, LIMESTONE ,DOLOMITE..

4. BERASAL DARI BATUAN BEKU BASA ATAU SEMIBASIC ROCKS (TERMASUK TUFF) DENGAN IMPURITIES Ca, Al, Mg, Fe DALAM JUMLAH YANG BERARTI.

5. BATUAN MAGNESIAN DAI BATUAN SERPENTINE DAN SEDIMENT CHLORITIC ATAU BATUAN LAINNYA YANG KAYA DENGAN Fe DAN Mg.

- DASAR TEKSTUR DAN MINERAL YANG MUDAH DIKENALI SECARA MEGAS KOPIK.- ANALISA MIKROSKOP DIPERLUKAN BILA AKAN DILAKUKAN PEMBAGIAN LEBIH LANJUT DENGAN DASAR MINERAL DAN FASIES METAMORF.URE- MINERALOGICAL DAN TEXTURE CHARACKTERISTIC YANG - DIPAKAI SEBAGAI DASAR KLASIFIKASI DIPILIH SEDEMIKIAN RUPA SEHINGGA PENGGOLONGAN DILAKUKAN ATAS BATUAN INDUK YANG SAMA DAN MENGALAMI KONDISI METAMORFOSA YANG SAMA PULA.

DASAR KLASIFIKASI

- ANALISA MIKROSKOP DIPERLUKAN BILA AKAN DILAKUKAN PEMBAGIAN LEBIH LANJUT.

- MINERALOGI DAN KARAKTERISTIK YANG DIPAKAI SEBAGAI DASAR KLASIFIKASI, DIPILIH SEDEMIKIAN RUPA SEHINGGA PENGGOLONGAN DILAKUKAN ATAS BATUAN INDUK YANG SAMA DAN MENGALAMI KONDISI METAMORFOSA YANG SAMA PULA.

DASAR TEKSTUR DAN MINERAL YANG MUDAH DIKENALI SECARA MEGASKOPIK.

A. FOLIATED ROCKS

B. TANPA FOLIASI

Classification of Major Metamorphic Rockstexture and mineral composition

Shale is a fine-grained sedimentary rock that forms from the compaction of silt and clay-size mineral particles that we commonly call "mud". This composition places shale in a category of sedimentary rocks known as "mudstones". Shale is distinguished from other mudstones because it is fissile and laminated. "Laminated" means that the rock is made up of many thin layers. "Fissile" means that the rock readily splits into thin pieces along the laminations.

SHALE is a fine-grained sedimentary rock that forms from the compaction of silt and clay-size mineral particles that we commonly call "mud". This composition places shale in a category of sedimentary rocks known as "mudstones". Shale is distinguished from other mudstones because it is fissile and laminated. "Laminated" means that the rock is made up of many thin layers. "Fissile" means that the rock readily splits into thin pieces along the laminations

Shale: Shale breaks into thin pieces with sharp edges. It occurs in a wide range of colors that include: red, brown, green, gray, and black. It is the most common sedimentary rock and is found in sedimentary basins worldwide.

Shales have fissility that is caused by the preferred orientation of clay minerals with their {001} planes orientated parallel to bedding.   Metamorphic petrologists and structural geologists refer to the original bedding surface as S0.

 

the maximum principle stress is oriented at an angle to the original bedding planes so that the slatey cleavage develops at an angle to the original bedding. The foliation or surface produced by this deformation is referred to S1.

SLATE  Slates form at low metamorphic grade by the growth of fine grained chlorite and clay minerals. The preferred orientation of these sheet silicates causes the rock to easily break planes parallel to the sheet silicates, causing a slatey cleavage.

SLATY TEXTURE - this texture is caused by the parallel orientation of microscopic grains. the name for the rock with t his texture is slate , and the rock is characterized by a tendency to separate along parallel planes. this feature is a property known as slaty cleavage

PHYLLITE is between slate and schist in the spectrum of metamorphic rocks. Phyllite generally is in the pelitic series—rocks that are derived from clay sediments—but sometimes other rock types can take on the characteristics of phyllite too.

PHYLLITE is a textural rock type, not a compositional one. The sheen of phyllite is from microscopic grains of mica, graphite, chlorite and similar minerals that form under moderate pressure.

SCHIST - The size of the mineral grains tends to enlarge with increasing grade of metamorphism.  Eventually the rock develops a near planar foliation caused by the preferred orientation of sheet silicates (mainly biotite and muscovite).  Quartz and feldspar grains, however show no preferred orientation.  The irregular planar foliation at this stage is called schistosity

SCHISTOSE TEXTURE this is a foliated texture resulting from the suhparallel to parallel orientation of platy minerals such as chlorite or micas. other common minerals present are quartz and amphiholes.

These dark colored minerals tend to become segregated into distinct bands through the rock (this process is called metamorphic differentiation), giving the rock a gneissic banding.  Because the dark colored minerals tend to form elongated crystals,  rather than sheet- like crystals, they still have a preferred orientation with their long directions perpendicular to the maximum differential stress.

GNEISS  As metamorphic grade increases, the sheet silicates become unstable and dark colored minerals like hornblende and pyroxene start to grow.

GNEISSIC TEXTURE this is a coarsely foliated texture in which the minerals have been segregated into discontinuous hands, each of which is dominated by one or two minerals. these bands range in thickness from 1 mm to several centimeters.

 

GRANULITE - At the highest grades of metamorphism most of the hydrous minerals and sheet silicates become unstable and thus there are few minerals present that would show a preferred orientation.  The resulting rock will have a granulitic texture that is similar to a phaneritic texture in igneous rocks.

In general, the grain size of metamorphic rocks tends to increase with increasing grade of metamorphism, as seen in the progression form fine grained shales to coarser (but still fine) grained slates, to coarser grained schists and gneisses.

HORNFELS : NON SCHISTOSE ROCKS yang dibentuk oleh suatu mozaik butiran equidimensional tanpa orientasi tertentu (granoblastic atau hornfels texture), (porhyroblast dapat dibungkus oleh matrix granoblastic).

HORNFELS

QUARTZITE

KLASIFIKASI BERDASARKAN

“KEJADIAN”

DAN

“TEMPAT KEJADIAN”.

I. BERDASARKAN KEJADIAN DAN TEMPAT KEJADIAN. 1. Regional Metamorphism. .•Tipe ini berkaitan dengan peristiwa orogenesa, temperatur dan tekanan memegang peran yang penting, baik karena kompresi maupun pembebanan.•Batuan metamorf regional tedapat pada daerah yang sangat luas , 10 – 100 km lebar dan 100 – 1000 km panjang. 2. Contact Metamorphism.• Rekritalisasi, pembentukan himpunan mineral2 metamorfik, di daerah kontak sekitar badan intrusi.•Biasa terjadi pada Tekanan yang konstan dan metamorfosa terjadi karena peningkatan Temperatur, karena adanya penghantaran panas keluar badan intrusi. 3. Pyro Metamorphism.•Rekristalisasi pada temperatur tinggi terhadap sebuah “xenolith” dalam volkanisma atau intrusi.•Pelelehan xenolith. 4. Cataclastic Metamorphism.

Crushing or grinding of rocks sebagai hasil gerak sesar.

REGIONAL METAMORPHISM

• Regional Metamorphism sensu lato– metamorphism that affects a large body of rock, and thus covers a great lateral extent

• Three principal types– Orogenic metamorphism– Burial metamorphism– Ocean-floor metamorphism.

OROGENIC METAMORPHISM Type of metamorphism associated with convergent plate margins

Dynamo-thermal, involving one or more episodes of orogeny with combined elevated geothermal gradients and deformation (deviatoric stress). Foliated rocks are a characteristic product. Uplift and erosion

Metamorphism often continues after major deformation ceasesMetamorphic pattern is simpler than the structural one

Pattern of increasing metamorphic grade from both directions toward the core areaMost orogenic belts have several episodes of deformation and metamorphism, creating a more complex polymetamorphic pattern

Associated with continental collisionBatholiths are usually present in the highest grade areas If plentiful and closely spaced, may be called regional contact metamorphism

Regional Metamor

phism

Contact Metamorphism• The size and shape of an aureole is controlled by

– The nature of the pluton.– The nature of the country rocks.– Most easily recognized where a pluton is introduced into shallow rocks in

a static environment.– The rocks near the pluton are often high-grade rocks with an isotropic

fabric: hornfelses (orgranofelses) in which relict textures and structures are common

Polymetamorphic rocks are common, usually representing an orogenic event followed by a contac zone, e.g. spotted phyllite or slate

Overprint may be due to: Pyrometamorphism

• Very high temperatures at very low pressures, generated by a volcanic or subvolcanic body

• Also developed in xenoliths• Not very common and won’t be looked at further in this course.

Regional MetamorphismBURIAL METAMORPHISM : Low grade metamorphism in sedimentary basins due to burial.

• Example: Southland Syncline in New Zealand

– A thick pile (> 10 km) of Mesozoic volcaniclastics had accumulated

– Mild deformation and no igneous intrusions discovered

– Fine-grained, high-temperature phases, glassy ash: very susceptible to metamorphic alteration

– Metamorphic effects attributed to increased pressure and temperature due to burial

– Range from diagenesis to the formation of zeolites, prehnite, pumpellyite, laumontite, etc.• Bengal Fan represents a sedimentary pile > 22 km - Extrapolating implies 250-300oC at the base (P ~ 0.6 GPa). - Well into the metamorphic range, and the weight of the overlying sediments is sufficient to impart a foliation at depth

- Passive margins often become active - Areas of burial metamorphism may thus become areas of orogenic metamorphism. - Occurs in areas that have not experienced significant deformation or orogeny - Restricted to large, relatively undisturbed sedimentary piles away from active plate margins.

Regional MetamorphismOCEAN-FLOOR METAMORPHISM

• Affects the oceanic crust at ocean ridge spreading centres

– Wide range of temperatures at relatively low pressure, beginning in the diagenesis field and increasing to lower greenschist facies

– Metamorphic rocks exhibit considerable metasomatic alteration, notably loss of Ca and Si and gain of Mg and Na

– These changes can be correlated with exchange between basalt and hot seawater

– We’ve seen this already when we looked at the Cyprus thin-sections!.

• May be considered another example of hydrothermal metamorphism• Highly altered chlorite-quartz rocks- distinctive high-Mg, low-Ca

composition

.

DASAR TEMPERATUR DAN TEKANAN.DERAJAT METAMORFOSA1. LOW GRADE METAMORPHIC ROCKS.2. MEDIUM GARDE METAMORPHIC ROKS.3. HIGH GRADE METMORPHC ROCKS.

DASAR KOMPOSISI BATUAN ASAL.

1. BERASAL DARI PELITIC (ALLUMINOUS ) SEDIMENT :CLAY, SAHLES, MUDSTONE).

2. BERASAL DARI QUARTZO-FELDSPATHOID ROCKS (BATUAN BEKU ASAM).

3. BERASAL DARI CALCAREOUS SEDIMENT, LIMESTONE ,DOLOMITE.

4. BERASAL DARI BATUAN BEKU BASA ATAU SEMIBASIC ROCKS (TERMASUK

TUFF) DENGAN IMPURITIES Ca, Al, Mg, Fe DALAM JUMLAH YANG BERARTI.

5. BATUAN MAGNESIAN DAI BATUAN SERPENTINE DAN SEDIMENT CHLORITIC ATAU BATUAN LAINNYA YANG KAYA DENGAN Fe DAN Mg.

BARROW'S ZONES

ZONASI M E T A M O R F O S A

George Barrow mapped a widespread series of zones of progressive metamorphism. Barrow recognized the existence of unmetamorphosed shaley (pelitic) sediments which subsequently underwent metamorphism.

Each zone recognized is based on the first appearance of a group of distinctive index minerals as the highest metamorphic grade, along the thermal axis. Any mineral within the zone may be the index mineral.

Each zone recognized is based on the first appearance of a group of distinctive index minerals as the highest metamorphic grade, along the thermal axis, was approached.

Index mineral is one which is characteristic of that zone - any mineral within the zone may be the index mineral.

BARROW'S ZONES

In the Barrovian sequence (described by George Barrow in zones of progressive metamorphism in Scotland), metamorphic grades are also classified by mineral assemblage based on the appearance of key minerals in rocks of pelitic (shaly, aluminous) origin:Low grade ------------------- Intermediate --------------------- High grade

Greenschist ------------- Amphibolite ----------------------- GranuliteSlate --- Phyllite ---- Schist --------- Gneiss -----------------------Migmatite(partial melting) >>>meltChlorite zone Biotite zone Garnet zone Staurolite zone Kyanite zone Sillimanite zone

T dan P naik

•Zone of digested clastic mica1.Now termed chlorite zone - characterized by first appearance of chlorite. 2.The characteristic assemblage - quartz-chlorite-muscovite-albite.

•Biotite Zone Marked by the first appearance of red-brown biotite produced from reaction between muscovite and chlorite. •Garnet ZoneThe characteristic assemblage recognized by Barrow is quartz-muscovite-biotite-almandine (Fe,Mg)3Al2Si3O12-albite or oligoclase. •Staurolite ZoneThe assemblage is quartz-muscovite-biotite-almandine-staurolite-(oligoclase) •Kyanite ZoneAssemblage is quartz-biotite-muscovite-oligoclase-almandine-kyanite •Sillimanite Zonequartz-biotite-muscovite-oligoclase-almandine-sillimanite

PAIRED METAMORPHIC

Figure) Myoshira was actually mapping the location of ancient subduction zones. High P low T belt marked the trench where plates were colliding, hence high pressure. Low temperature due to the cooling effect of seawater. Landward the rising plutons from the zone of partial melting caused the local high temperatures at relatively shallow depth. Oceanward facies is the blueschist and landward a combination amphibolite and granulite.

Akiho Miyashiro in 1961, recognized that many metamorphic belts of different ages around the world exhibited one or other of the following sequences of metamorphic grade in going from low to high grade:

prehnite–pumpellyite → blueschist → greenschist or amphibolite greenschist → amphibolite → granulite

Miyashiro used the term facies series for these characteristic associations of facies and pointed out that they distinguished contrasting baric (pressure-) types of metamorphism; in the first instance high pressures were attained at relatively low temperatures, indicative of a low heat-flow setting, whereas in the second instance temperatures rose rapidly at shallow levels, indicating high heat flow. The classical metamorphic zones known from the work of George Barrow are representative of an intermediate pressure association corresponding approximately to a normal crustal thermal gradient.

Miyashiro also believed that belts of contrasting facies series and of the same age commonly occurred together. He called this association paired metamorphic belts. With the advent of plate-tectonic theory, Miyashiro was quick to recognize the tectonic significance of the different facies series. The low heat flow associated with high-pressure metamorphism and the development of blueschists is indicative of a subduction zone setting; the elevated heat flow and associated magmatism associated with low-pressure metamorphism is usually indicative of the roots of a volcanic arc.

Paired Metamorphic Belts of Japan.Fig. 16-15 suggests that the 600oC isotherm, for example, could be as deep

as 100 km in the trench-subduction zone area, and as shallow as 20 km beneath the volcanic arc

Paired Metamorphic Belts of Japan.The Sanbagawa and Ryoke

metamorphic belts of Japan.

The NW belt (“inner” belt, inward, or away from the trench) is The NW belt (“inner” belt, inward, or away from the trench) is the the RyokeRyoke (or (or AbukumaAbukuma) ) BeltBelt..

Low P/TLow P/T Buchan-type of regional orogenic Buchan-type of regional orogenic metamorphismmetamorphism..

Dominant meta-pelitic sediments, and isograds up to Dominant meta-pelitic sediments, and isograds up to the sillimanite zone have been mappedthe sillimanite zone have been mapped..

A A high-temperature-low-pressurehigh-temperature-low-pressure belt, and granitic belt, and granitic plutons are commonplutons are common..

• Outer belt, called the Outer belt, called the Sanbagawa BeltSanbagawa Belt

• It is of a It is of a high-pressure-low-temperaturehigh-pressure-low-temperature nature nature Only reaches the garnet zone in the pelitic rocksOnly reaches the garnet zone in the pelitic rocks BasicBasic rocks are more common than in the Ryoke rocks are more common than in the Ryoke

belt, however, and in these belt, however, and in these glaucophaneglaucophane is developed is developed (giving way to hornblende at higher grades) (giving way to hornblende at higher grades)

Rocks are commonly called Rocks are commonly called blueschistsblueschists

• Two belts are in contact along their whole length across a major fault zone (the Median Line)

• Ryoke-Abukuma lithologies are similar to seds derived from a relatively mature volcanic arc

• Sanbagawa lithologies more akin to the oceanward accretionary wedge where distal arc-derived sediments and volcanics mix with oceanic crust and marine sediment

selanjutnya kembangkan dengan membaca dan lapangan.

selesai ???......... konsep dasar......!!!!!.

TEKSTUR UTAMA BATUAN METAMORF. (BEN HARTE)

1.GRANULAR IGNEOUS TEXTURE (EQUANT ATAU TABULAR).

2.FRAMED PORPHYROBLASTIC.

3.PORPHYROBLASTIC MOSAIC.

4.GRANOBLASTIC MOSAIC.

5. DAN 6. SECONDARY ANNEALING TEXTURE.

7. MESOCOPIC TEXTURAL CONTRAST OF A MYLONITE.

Foliation is defined as a pervasive planar structure that results from the nearly parallel alignment of sheet silicate minerals and/or compositional and mineralogical layering in the rock. Most foliation is caused by the preferred orientation of phylosilicates, like clay minerals, micas, and chlorite.  Preferred orientation develops as a result of non-hydrostatic or differential stress acting on the rock (also called deviatoric stress).  We here review the differences between hydrostatic and differential stress.

T E K S T U R

Thus, if a differential stress is acting on the rock, the direction along which the maximum principal stress acts is called s1, the minimum principal stress is called s3, and the intermediate principal stress direction is called s2.   Note that extensional stress would act along the direction of minimum principal stress. 

SCHISTOSE TEXTURE THIS IS A FOLIATED TEXTURE RESULTING FROM THE SUHPARALLEL TO PARALLEL ORIENTATION OF PLATY MINERALS SUCH AS CHLORITE OR MICAS. OTHER COMMON MINERALS PRESENT ARE QUARTZ AND AMPHIHOLES. A SCHISTOSE TEXTURE LIES BETWEEN THE PARALLEL PLATY APPEARANCE OF PHYLLITE AND THE DISTINCT BANDING OF GNEISSIC TEXTURE. THE AVERAGE GRAIN SIZE OF THE MINERALS IS GENERALLY SMALLER THAN IN A GNEISS. A ROCK WITH SCHISTOSE TEXTURE IS CALLED A SCHIST

PHYLLITIC TEXTURE - THIS TEXTURE IS FORMED BY THE PARALLEL ARRANGEMENT OF PLATY MINERALS, USUALLY MICAS, THAT ARE BARELY MACROSCOPIC (VISIBLE TO THE NAKED EYE). THE PARALLELISM IS OFTEN SILKY, OR CRENULATED. THE PREDOMINANCE OF MICACEOUS MINERALS IMPARTS A SHEEN TO THE HAND SPECIMENS. A ROCK WITH A PHYLLITIC TEXTURE IS CALLED A PHYLLITE.

TANPA FOLIASI :1.CATACLASTIC TEXTURE. 2. PROTOCLASTIC TEXTURE.

gneissic texture this is a coarsely foliated texture in which the minerals have been segregated into discontinuous hands, each of which is dominated by one or two minerals. these bands range in thickness from 1 mm to several centimeters. the individual mineral grains are macroscopic and impart a striped appearance to a hand specimen. light-colored bands commonly contain quartz and feldspar. and the dark hands are commonly composed of hornblende and hiotite. accessory minerals are common and are useful in applying specific names to these rocks. a rockwith a gneissic texture is called a gneiss.

HORNFELSHORNFELS

HORNFELS : NON SCHISTOSE ROCKS YANG DIBENTUK OLEH SUATU MOZAIK BUTIRAN EQUIDIMENSIONAL TANPA ORIENTASI TERTENTU (GRANOBLASTIC ATAU HORNFELS TEXTURE), (PORHYROBLAST DAPAT DIBUNGKUS OLEH MATRIX GRANOBLASTIC).

QUARTZITE

Types of MetamorphismGeologists suggest that metamorphism can occur by way of the following three processes.Thermal metamorphism involves the heating and structural and chemical alteration of rocks through processes associated with plate tectonics. This type of metamorphism has two sub-categories: Regional metamorphism is the large scale heating and modification of existing rock through the creation of plutons at tectonic zones of subduction. It involves large areas and large volumes of rock.Contact metamorphism is the small scale heating and alteration of rock by way of a localized igneous intrusion (for example, volcanic dykes or sills). Dynamic metamorphism causes only the structural alteration of rock through pressure. The minerals in the altered rocks do not change chemically. The extreme pressures associated with mountain building can cause this type of metamorphism.Metasomatic metamorphism involves the chemical replacement of elements in rock minerals when gases and liquids permeate into bedrock.

Figure 1-9. Estimated ranges of oceanic and continental steady-state geotherms to a depth of 100 km using upper and lower limits based on heat flows measured near the surface. After Sclater et al. (1980), Earth. Rev. Geophys. Space Sci., 18, 269-311.

BATUAN METAMORF/UBAHAN

Metamorphic rock, ........ adalah batuan hasil ubahan dari batuan yang sudah ada. “Protolith”, oleh sebuah proses yang disebut sebagai proses metamorfosa, yang berarti “berubah dalam bentuk”.“Protolith” adalah objek dari panas dan tekanan (T > 150 - 200 °C dan tekanan 1500), dapat berupa batuan sedimen, batuan beku ataupun batuan metamorf .Batuan metamorf menyusun sebagain besar dari kerakbumi dan dikalsifikasikan berdasarkan tekstur, kimia ataupun himpunan mineral pembentuknya. Batuan ini secara sederhananya terbentuk karena berada dikedalaman yang besar dipengaruhi oleh temperatur dan tekanan yang dibentuk beban diatasnya.Dapat terjadi karena tektonik seperti “continental collosion” yang menimbulkan tekanan horisontal, gesekan dan distortion. Juga dapat terbentuk karena pemanasan dari intrusi magma yang panas.

BATUAN METAMORF ATAU BATUAN UBAHAN ADALAH BATUAN HASIL PERUBAHAN DARI, BATUAN BEKU, BATUAN SEDIMEN, ATUAPUN BATUAN METAMORF LAIN, YG SUDAH ADA SEBELUMNYA. BATUAN INI DIBENTUK KARENA ADANYA PENGARUH PANAS, DAN TEKANAN YANG TINGGI, ATAUPUN CAMPURAN KEDUANYA.

• The IUGS-SCMR has proposed the following definition of metamorphism:

Metamorphism is a subsolidus process leading to changes in mineralogy and/or texture (for example grain size) and often in chemical composition in a rock. These changes are due to physical and/or chemical conditions that differ from those normally occurring at the surface of planets and in zones of cementation and diagenesis below this surface. They may coexist with partial melting.”

Metmorfosa adalah sebuah proses “subsolidus” yang mengarah ke perubahan dalam mineralogi dan/atau tekstur juga, seringkali dalam komposisi kimia dalam sebuah sebuah batuan.Perubahan ini dikarenakan kondisi fisik dan/atau kimia yang berbeda dengan yang umum yang terjadi dipermukaan planet dan dalam zona sementasi dan diagenesa dibawah permukaan, Mereka mungkin bekerja sama (koeksis) dengan “pertial melting”.

•Zeolite Facies 1.Zeolites are groups of white to colourless hydrous alumina silicates, analogous in composition to feldspars. 2.Laumontite, heulandite and analcine are common, the assemblage Quartz + Laumontite + Chlorite is diagnostic.

•Prehnite - Pumpellyite 1.Prehnite +/- Pumpellyite + Quartz is typical. 2.Prehnite - Ca2Al2Si3O10(OH)2 Pumpellyite - Ca2MgAl2(SiO4)(Si2O7)(OH)2H2O

•Glaucophane - Lawsonite Schist or Blueschist1.High P Low T 2.Glaucophane (Na2MgAl2Si8O22(OH)2) (alkali-rich amphibole) + Lawsonite .3.(CaAl2Si2O7(OH)2H2O) arecharacteristicalso 4.Jadiete (NaAlSi2O6) + Qtz + Aragonite

•Greenschist 1.Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks 2.pyrophyllite in pelitic rocks

•Amphibolite 1.Hornblende + Plagioclase (An > 20) 2.Kyanite (Al2SiO5) in pelites

•Granulite1.lower crustal lithology 2.cpx + opx + plag + Fe - Mg garnet

•Eclogite 1.lower crust or upper mantle lithology 2.Feldspar-free assemblages, with jadiete-rich cpx + pyrope (Mg-rich garnet)

Perkiraan berkisar antara geotermal samudra dan geotermal Perkiraan berkisar antara geotermal samudra dan geotermal benua; sampai dengan kedalaman 100 km; menggunakan limit benua; sampai dengan kedalaman 100 km; menggunakan limit atas dan bawah, berdasarkan pengukuran “heat flows” dekat atas dan bawah, berdasarkan pengukuran “heat flows” dekat permukaan. (Schlater, et al; 1980). permukaan. (Schlater, et al; 1980).

Rekristalisasi menghasilkan perubahan ukuran butir; rasio volume butir Rekristalisasi menghasilkan perubahan ukuran butir; rasio volume butir besar besar

terhadap butir kecil, menunjukan nilai stabilitas rendah.terhadap butir kecil, menunjukan nilai stabilitas rendah.

PROSES METAMORFOSA DIBEDAKAN MENJADI:o Regional Metamorphism

• Orogenic Metamorphism• Burial Metamorphism• Ocean Floor Metamorphism

o Contact Metamorphism• Pyrometamorphism

o Hydrothermal Metamorphismo Fault Zone Metamorphism .o Impact or Shock Metamorphism

M E T A M O R F O S A …….proses. asal kata : META .......UBAH. dan MORF ......... BENTUK P E R U B A H A N B E N T U K.

T &

P

T &P

T &

P

T &

P

Batuan metamorf menyusun sebagain besar dari kerakbumi dan diklasifikasikan berdasarkan tekstur, kimia ataupun himpunan mineral pembentuknya.

Dapat terjadi karena tektonik seperti “continental collosion” yang menimbulkan tekanan horisontal, gesekan dan distortion. Juga dapat terbentuk karena pemanasan dari intrusi magma yang panas.