acara 2 petrologi 2012
TRANSCRIPT
Introduction to Petrography
Week #2Assistants : Feisal Dirgantara
… what we’ve learned from last week
How to learn petrology
•Outcrop
•Hand sample
•Thin section
•Chemistry
•Experimental Studies
Importance of petrography
• Petrogenesa
• Mineral composition and abundance
• What have altered after lithification
• Environmental of Deposition
• Type of deposition
• Post lithification structure, e.g stylolite, bioturbation, karstification
Light as wave-particle duality• Light as wave• Radiated energy which vibrates
at certain angle to the direction of motion
• Important characteristics :
• Amplitude
• Frequency
• Wave length
C = f.λ
• Light as particle
– When a photon is created, the light particle comes in and hits the electron so that it moves to the next energy cloud
– Due to instability of energy, the electron will bounce back to originial energy state and emits photon away
Oxygen (8O)
:: Light as wave-approach is the basis for petrography analysis
Snell’s Law
Θ2 : θ1 = C2 : C1 = λ2 : λ1
C = f.λ
θ1
θ2
air
Qz
Light’s polarization
• Normally, a light vibrates in circular polarization.
• A polarizer will adjust light wave to move in a specific polarization without changing its characteristic (wavelength, amplitude, speed, frequency).
Petrography microscope
Glossary in petrography• anisotropic mineral: A mineral with more than one principal
refractive index.
• birefringence: The mathematical difference between the largest and smallest refractive index for an anisotropic mineral.
• biaxial mineral: A mineral with three principal refractive indices and two optic axes. Its indicatrix is a triaxial ellipsoid.
• dispersion: Change of any optical property with wavelength.
• indicatrix: The three-dimensional surface describing the variation in refractive index with relationship to vibration direction of incident light.
• optical orientation: The relationship between a mineral's crystallographic axes and optical indicatrix.
• pleochroism: The property of exhibiting different colors as a function of the vibration direction.
• uniaxial mineral: A mineral with two principal refractive indices and one optic axis. Its indicatrix is a prolate or oblate ellipsoid.
• optical class: One of five possible classes (different indicatrices) to which a mineral can belong: isotropic, uniaxial +/-, or biaxial +/-.
• isotropic mineral: A mineral with the same refractive index regardless of vibration direction. Its indicatrix is a sphere.
Igneous Petrography
Week #2Assistants : Sony Adam, Ragil Yuni
1) Light passes through the lower polarizer
west (left)
east (right)
Plane polarized light“PPL”
Unpolarized light
Only the component of light vibrating in E-W direction can pass through lower polarizer – light intensity
decreases
PPL
XPL
west (left)
east (right)XPL
(crossed nicols or crossed polars)
south (front)
north (back)
Black!“extinct”
2) Insert the upper polarizer
Now what happens?What reaches your eye?
Why would anyone design a microscope that prevents light from reaching your eye?
3) Now insert a thin section of a rock
west (left)
east (right)
Light vibrating E-W
Light vibrating in many planes and
with many wavelengths
Unpolarized light
Light and colors reach eye!
XPL
PhotomicrographConclusion has to be that minerals somehow reorient the planes in
which light is vibrating; some light passes through the upper polarizer
PPL XPL
What are you looking for inPPL XPL• Color• Cleavage• Habit
• Grain boundaries• Twinning• Birefringence
Color• Color is observed only in PPL• Not an inherent property - changes with light type/intensity• Results from selective absorption of certain l of light
plag
hbl
-Plagioclase is colorless-Hornblende is olive greens
Cleavage• No cleavages: quartz, olivine• 1 good cleavage: micas• 2 good cleavages: pyroxenes, amphiboles
Cleavage
2 cleavages intersectingat ~90° pyroxene
60°
120°
2 cleavages intersectingat 60°/120°: amphibole
prismatic
anhedral/irregular
elongate
fibrous
tabular
euhedral
Habits
prismatic
anhedral/irregular
elongate
fibrous
tabular
euhedral
Habits
Birefringence, XPL Color Spectrum
Twinning
• Not only in hand samples
• Under the microscope • Parts will be extinct
while the other will show a true XPL color
• Very common in Plagioclase Feldspar
Degree of Crystallization
Holokristalin
Holocrystalline - composed wholly of crystalsHypocrystalline - contains both glass and crystalsHolohayline - consists entirely of glass
Granular TexturePanidiomorphic-granular (automorphic-granular) - the chief minerals are euhedral
Hypidiomorphic-granular (hypautomorphic-granular or granitic) - some constituents are euhedral, some subhedra, and the rest anhedral
Allotriomorphic-granular (xenomorphic-granular or aplitic or sugary or saccaharoidal ) – almost all of the constituents are anhedral
Porfiro-aphanitic Phaneritic
Quartz
Plagioclase & K-Feldspar
Biotite
Muscovite
Hornblende
Pyroxene (CPX & OPX)
Olivine
MineralPPL XPL
Warna Belahan Habit Twinning Birefringence
QZ Colorless -AnhedraIrregular
-1st
Abu - Putih
PLAG Colorless - Tabular Ya 1st
KSPARColorless
Abu- Tabular Ya 1st - Abu
BIOCoklatHijau
1 Tabular -Up to 2nd
Red
MUS Colorless 1 Tabular -Up to 2nd
Red
HRBHijauCoklat
2 (60°)Any
Anhedra-
Up to mid2nd
OPX Colorless 2 (90°)Any
Anhedra-
Up to 1st
Yellow
CPX Colorless 2 (90°)Any
Anhedra-
Up to high2nd
OLV Colorless - Tabular -Up to high
3rd
G Colorless - Anhedra - Black
OPQ Black - Anhedra - Black
Komposisi Mineral:• 60% Olivin. PPL: Tidak berwarna, Belahan poor, Habit: euhedral. XPL: No Twinning, Interferensi orde 2 sampai 3.
25% Plagioklas menjadi massa dasar.
15% Mineral Opaque. PPL: Warna hitam, habit: subhedral. XPL: Tak tembus/Orde 1, hadir setempat-setempat dalam sayatan
Tekstur:• Teksturnya adalah holokristalin, karena sebagian besar kristal• Komponen kristalnya porfiritik pada massa dasar yang afanitik• Fenokrisnya olivin yang euhedra sampai subhedra, dan beberapa plagioklas yang anhedra• Tekstur granularitasnya panidiomorfik granular.
Sedimentary Petrography
Week #2Assistants : Paula Ascariyani E Agung Dwi A.
Siliciclastics
Petrografi Batuan Sedimen
Jenis dari Batuan sedimen, berdasarkan mekanisme sedimentasinya
•Dentrital
•Nondentrital / Authigenic
Komposisi batuan sedimen, dilihat dari batuan induknya• Menunjukkan bagian besar yang sama dari
sedimen dentrital.
• Karena Diagenesis , maka batuan memiliki bentuk yang benar2 berbeda dari batuan induknya.
• Terlihat komposisi batuan berupa mineral yang stabil seperti Quartz, Mica, dan Feldspar.
Akibat Transportasi dan Deposisi
• perubahan fisik dari batuan, perubahan dari bentuk, ukuran, dan derajat kebolaan. Karena proses sortasi dan abrasi.
• perubahan fisik dari batuan, perubahan dari bentuk, ukuran, dan derajat kebolaan. Karena proses sortasi dan abrasi.
Akibat Transportasi dan Deposisi
• Partikel ukuran paling besar dan densitas besar, akan terdeposisi pertama kali.
• Perubahan secara fisik ini akan terlihat dan mencirikan tekstur dari batuan sedimen.
UKURAN BUTIR
UKURAN BUTIRUkuran butir akan menunjukkan energi pengendapan
Ukuran kecil = energi kecilUkuran besar = energi besar
–Ketika aliran sedikit memelan, hanya kan mengendapkan partikel yg terbesar dan mengendapkan sedimen dengan sortasi yang baik.
–Ketika aliran semakin pelan, akan mengendapkan partikel sedimen dg ukuran yg bervariasi (semua ukuran, diatas kompetensi yg baru), dan akan mengendapkan sedimen dg sortasi buruk.
SORTASI DAN BENTUK BUTIR
• 1. SORTASI
• 2. BENTUK BUTIR
HUBUNGAN ANTAR BUTIR
Line of Traverse(using microscope)
Cement
Matrix(clays, etc.)
Tangential Contact
Sutured Contact
Long Contact
Concavo-ConvexContact
HUBUNGAN ANTAR BUTIR
(modified from Blatt, 1982)
HUBUNGAN ANTAR BUTIR
TIPE POROSITAS
TIPE POROSITAS
KOMPOSISI
KLASIFIKASI
After Pettijohn et al. (1987)
KOMPONEN SILISIKLASTIK
1. PASIR SILISIKLASTIK
• Kuarsa, Feldspar, dll
2. MUD
• Mineral Lempung
CONTOH SAYATAN
Feldspar Plagioklas
K-Fldspar
Karbonat
FELDSPATHIC ARENITE
HANDSPECIMEN FELDSPATHIC ARENITE
CONTOH SAYATAN
QUARTZ ARENITE
Long contact
Sutured contact
Point contact
Convex -concav
HANDSPECIMEN QUARTZ ARENITE
LITHIC ARENITE
Lithic
Semen
Carbonates
Definisi
• Syarat Kondisi : (dominan dari proses biogenik) -> air laut• Hangat -> 19o - 25o C (zona photic dan iklim
tropis)
• Tenang arusnya
• Suplai sedimen darat minimum
Komponen Utama Batuan Karbonat
KLASIFIKASI
Folk Klasifikasi
Dunham Klasifikasi
Embry Klovan Klasifikasi
KEY : TEKSTUR PENGENDAPAN (ALLO ATAU AUTO)
Packestone
Grainstone
Floatstone
Rudstone
Matriks Supp
Grain Supp
Porositas
• Porositas intergranular, yaitu ruang pori yang terbentuk antar butiran partikel atau fragmen material klastik akibat batuan yang memiliki kemas lepas (looses packing), terkompaksi atau tersementasi.
• Porositas intragranular atau interkristalin, terbentuk akibat adanya shrinking (lenyapnya butiran akibat reaksi kimia) atau kontraksi butiran.
• Porositas rekahan, diakibatkan oleh adanya proses mekanik atau proses kimiawi secara parsial terhadap batuan yang masiv pada awalnya, seperti batu gamping. Porositas jenis ini merupakan porositas sekunder.
• Porositas vugular, adalah porositas yang dibentuk oleh organisme dan bersamaan dengan terjadinya proses/ reaksi kimia pada tahapan selanjutnya. Porositas ini merupakan jenis porositas primer dan sekunder.
Metamorphic Petrography
Week #2Assistants : Yuni Indrawati Fitrul Islam
• Klasifikasi batuan metamorf
• Tipe Metamorfisme :
Primary rocktype
Fineless than 1.0
mm
Medium1.0-5.0 mm
CoarseGreater than 5.0 mm
Diagnostic Minerals
PELITES Shales, mudstones and clays rich rocks. Aluminous.
Slate or phyllite Schist Gneiss, Migmatite
Quartz, White mica, biotite, chlorite, garnet, staurolite, andalusite/kyanite/sillimanite, cordierite, corundum, chloritoid.
PSAMMITES Sandstones, greywackes. quartz-feldspar rich minor mafics.
Quartzite Quartzite QuartziteQuartz, alkali feldspar, white mica, biotite, rare amphibole, chlorite.
CALCAREOUS Pure limestone's and dolomites. Ca, Si and Mg.
Marble Marble Marble Calcite, minor quartz and micas.
CALC-SILICATES Shaly and quartz rich dolomites and limestones. Marls. Ca and Si.
Calc-slate Calc-schist Calc-gneissCalcite, quartz, epidote, Ca-plagioclase, Grossular garnet, Diopside, Tremolite, Talc, Sphene, Forsterite, Actinolite.
QUARTZO-FELDSPATHIC Granitic and rhyolitic rocks. Quartz, feldspar, amphiboles and mica.
Halle-flintaAcid or granitic gneiss
Acid or granitic gneissQuartz, White mica, Biotite, Plagioclase, Alkali feldspar, Sphene.
MAFIC Gabbros and basaltic rocks Fe and Mg rich.
Greenstone Greenschist
AmphiboliteBasic, Hornblende or pyroxene gneiss
Epidote, Sphene, Calcite, Chlorite, Amphibole, Pyroxene, Plagioclase, Garnet, Serpentine, Talc.
ULTRAMAFIC peridotites, dunites pyroxenites, lacking feldspar. Very rich in Fe and Mg.
Serpentinite Talc-schist Soapstone
Ultrabasic gneissSerpentine, Talc, Phlogopite, Forsterite, Anthophyllite, Brucite, Enstatite, Magnesite-dolomite, Cordierite.
A. Granoblastik, B. Granoblastik (butir tak teratur), C. Schistose dengan porfiroblast, D. Schistose dengan granoblastik lentikuler, E. Filitik, F. Gneissose, G. Milonitik, H. filonitik, I. Granoblastik dalam milonit.
Bentuk Kristal Keterangan
(Euhedral) Staurolit, silimanit, kianit, rutil, klorit, ilmenit, turmalin, pirit, lawsonit, andalusit, garnet, sfen, epidot, zoisit, magnetit, spinel, ankerit, idokras
(Subhedral) Mika & klorit (memipih), amfibol & piroksen (prismatik), wolastonit, dolomit & apatit
(Anhedral) Kuarsa, felsfar, kalsit, aragonit, olivin, kordierit, scapolit, humites
Sketsa bentuk butir (kristal/mineral) a. euhedral, b. subhedral, c. anhedral
Tabel determinasi batuan metamorf
GARNET-AMPHIBOLITE
Bertekstur heteroblastik
terdiri dari mineral hornblende, garnet, mineral opak
terlihat struktur masif yang dominan oleh mineral garnet dan hornblenda
• Hornblende• 30 %
• Ukuran 0,2 – 1 mm
• Mineral nematoblastik
• Membentuk sekistose
• Berbentuk prismatik subhedral-anhedral
• Garnet• 45%• Ukuran 0,6 – 1,5• Phorphyroblastic• Membentuk sekistose• Berbentuk anhedral