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

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.

LIMITS OF METAMORPHISMbatas-batas peristiwa metamorfosa

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.

High Strain Rocks

PERISTIWA YANG BERLANGSUNG :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 + O2PROSES PEMBENTUKAN MINERAL.1. DALAM KEADAAN PADAT.DALAM SISTIM TERTUTUP.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 SiO21. CaMg(CO3)2 + SiO2 + H2O Mg2 Si4 O10 (OH)2 + 3 CaCO3 +3CO2 dolomit kuarsa talk kalsit 2. 5CaMg(CO3)2 + 8SiO2 + H2O Ca2Mg5 (Si4 O11)(OH)2 + 3 CaCO3 +7CO2 dolomit kuarsa remolit 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

TEKSTUR BATUAN METAMORF P E N A M A A N T E K S T U R

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

KESERAGAMAN UKURAN KRISTAL: ISOGRANULAR, ANEQUIGRANULAR .. PORPHYROBLAST.

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

B. TANPA FOLIASI :CATACLASTIC TEXTURE.PROTOCLASTIC TEXTURE. T E K S T U R U M U M

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

DASAR KLASIFIKASI

ANALISA MIKROSKOP DIPERLUKAN BILA AKAN DILAKUKAN PEMBAGIAN LEBIH LANJUT DENGAN DASAR MINERAL DAN FASIES METAMORF.

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 TEKSTUR DAN MINERAL YANG MUDAH DIKENALI SECARA MEGASKOPIK.

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 laminationsShale: 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.

PHYLLITE is between slate and schist in the spectrum of metamorphic rocks. Phyllite generally is in the pelitic seriesrocks that are derived from clay sedimentsbut 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.

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

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).

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 METAMORPHISMRegional Metamorphism sensu latometamorphism that affects a large body of rock, and thus covers a great lateral extentThree principal typesOrogenic metamorphismBurial metamorphismOcean-floor metamorphism.OROGENIC METAMORPHISM Type of metamorphism associated with convergent plate marginsDynamo-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 erosionMetamorphism often continues after major deformation ceasesMetamorphic pattern is simpler than the structural onePattern 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 patternAssociated with continental collisionBatholiths are usually present in the highest grade areas If plentiful and closely spaced, may be called regional contact metamorphism

Regional Metamorphism

Contact MetamorphismThe size and shape of an aureole is controlled byThe 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 commonPolymetamorphic rocks are common, usually representing an orogenic event followed by a contac zone, e.g. spotted phyllite or slateOverprint may be due to: PyrometamorphismVery high temperatures at very low pressures, generated by a volcanic or subvolcanic bodyAlso developed in xenolithsNot very common and wont be looked at further in this course.

Regional MetamorphismBURIAL METAMORPHISM : Low grade metamorphism in sedimentary basins due to burial.Example: Southland Syncline in New ZealandA thick pile (> 10 km) of Mesozoic volcaniclastics had accumulatedMild deformation and no igneous intrusions discoveredFine-grained, high-temperature phases, glassy ash: very susceptible to metamorphic alterationMetamorphic effects attributed to increased pressure and temperature due to burialRange 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 METAMORPHISMAffects the oceanic crust at ocean ridge spreading centresWide range of temperatures at relatively low pressure, beginning in the diagenesis field and increasing to lower greenschist faciesMetamorphic rocks exhibit considerable metasomatic alteration, notably loss of Ca and Si and gain of Mg and NaThese changes can be correlated with exchange between basalt and hot seawaterWeve seen this already when we looked at the Cyprus thin-sections!.May be considered another example of hydrothermal metamorphismHighly altered chlorite-quartz rocks- distinctive high-Mg, low-Ca composition

.

DASAR KOMPOSISI BATUAN ASAL.

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

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

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 ZONESZONASI 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

Zone of digested clastic micaNow termed chlorite zone - characterized by first appearance of chlorite. 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

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:

prehnitepumpellyite 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

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.

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 :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.

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

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/UBAHANMetamorphic 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.

Zeolite Facies Zeolites are groups of white to colourless hydrous alumina silicates, analogous in composition to feldspars. Laumontite, heulandite and analcine are common, the assemblage Quartz + Laumontite + Chlorite is diagnostic.Prehnite - Pumpellyite Prehnite +/- Pumpellyite + Quartz is typical. Prehnite - Ca2Al2Si3O10(OH)2 Pumpellyite - Ca2MgAl2(SiO4)(Si2O7)(OH)2H2O Glaucophane - Lawsonite Schist or BlueschistHigh P Low T Glaucophane (Na2MgAl2Si8O22(OH)2) (alkali-rich amphibole) + Lawsonite .(CaAl2Si2O7(OH)2H2O) arecharacteristic also Jadiete (NaAlSi2O6) + Qtz + Aragonite Greenschist Albite + Epidote + Actinolite + Chlorite + Calcite in mafic rocks pyrophyllite in pelitic rocks Amphibolite Hornblende + Plagioclase (An > 20) Kyanite (Al2SiO5) in pelites Granulitelower crustal lithology cpx + opx + plag + Fe - Mg garnet Eclogite lower crust or upper mantle lithology Feldspar-free assemblages, with jadiete-rich cpx + pyrope (Mg-rich garnet)

Perkiraan berkisar antara geotermal samudra dan geotermal benua; sampai dengan kedalaman 100 km; menggunakan limit atas dan bawah, berdasarkan pengukuran heat flows dekat permukaan. (Schlater, et al; 1980). Rekristalisasi menghasilkan perubahan ukuran butir; rasio volume butir besar terhadap butir kecil, menunjukan nilai stabilitas rendah.

PROSES METAMORFOSA DIBEDAKAN MENJADI:Regional MetamorphismOrogenic MetamorphismBurial MetamorphismOcean Floor MetamorphismContact MetamorphismPyrometamorphismHydrothermal MetamorphismFault Zone Metamorphism .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.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.

Especially for fine-grained and unstable materials in a static environment (shear stresses often reduce grain size)(a) = the incipient stages of subduction

(b) orogenic welt created by compression, crustal thickening, thrust stacking of oceanic slices, and addition of magmatic material from belowUnderthrusting in the forearc migrates trenchward, adding successive slabs to the base of the outer welt (tectonic underplating)Heat added by rising plutons, magmatically underplated magma, and induced mantle convection

Temperature increases both downward and toward the axial portion of the welt where plutons concentrated

A term coined by Coombs (1961) for low-grade metamorphism that occurs in sedimentary basins due to burial by successive layersCoombs worked in the Southland Syncline in New Zealand, where a thick pile (> 10 km) of Mesozoic volcaniclastics had accumulatedVariety of metamorphic minerals in ocean-floor rocks, representing a wide range of temperatures at relatively low pressureAlteration concentrated along vein systems, presumably associated with hydrothermal activity (note black smokers)Seawater penetrates down ubiquitous fracture systems, where it becomes heated, and leaches metals and silica from the hot basalts

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