Magma, Rocks Classification & Textures
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Transcript of Magma, Rocks Classification & Textures
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Magma, Rocks Classification & Textures
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MAGMA
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MAGMA
• Larutan silikat yang sangat panas• Mengandung oksida, sulfida serta
volatiles (CO2, sulfur, chlorine, fluorin, boron dll)
• Temperatur antara 600°C (magma asam) sampai 1250°C (magma basa)
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JENIS KONVERGEN
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Plate Tectonic - Igneous Genesis
? ???
600 km
400
200 km
Continental Crust
Oceanic Crust
Lithospheric Mantle
Sub-lithospheric Mantle
Source of Melts
15 3 46 7 2
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Environments of Magma Formation
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Environments of Magma Formation
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Stages in ascent
• EruptionEruption
• (Fragmentation)(Fragmentation)
• VesiculationVesiculation
• Renewed ascent Renewed ascent
• StorageStorage
– mixingmixing
– assimilationassimilation
– crystallizationcrystallization
• Buoyant ascentBuoyant ascent
• Partial meltingPartial melting
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The Earth’s InteriorThe Earth’s Interior
Crust:Crust:Granite/Andesite (felsic)Granite/Andesite (felsic)
Mantle:Mantle:Peridotite (ultramafic)Peridotite (ultramafic)
Core:Core:Metal alloy/liquidMetal alloy/liquid
6370
5145
2898
660
410
60220
Crust
MantleMantle
CoreCore
Upper Mantle
Transition Zone
Inner Core
Depth (km)
LowerMantle
(solid)
OuterCore
(liquid)
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Figure 1-5. Relative atomic abundances of the seven most common elements that comprise 97% of the Earth's mass. An Introduction to Igneous and Metamorphic Petrology, by John Winter , Prentice Hall.
O50.7%
Mg15.3%
Fe15.2%
Si14.4%
S3.0%
Al1.4%
Ca1.0%
Most important elementsMost important elements
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Partial Melting: The Origin of Basalt and Granite
Asthenosphere40% Silica
Melting
Basaltic magma = 50% silica (1100o C)
Forms the rock basalt
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Partial Melting: The Origin of Basalt and Granite
Continental Crust(Mainly low melting point minerals such as quartz, feldspar, mica)
Melting
Granitic magma ~ 70% silica (700-900o C)
Forms granite (a mixture of quartz and feldspar)
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Urutan pembekuan magma
• Pada pembekuan magma, pada awalnya mineral yang terbentuk adalah yang anhydrous (tidak mengandung air) tidak mengandung gugus OH, disebut mineral pyrogenetik.
• Cairan selanjutnya akan lebih banyak mengandung komponen gas dan terbentuk mineral-mineral yang mengandung gugusan hydroksil (OH), disebut mineral hydratogenetik.
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Diferensiasi Magma
• Proses diferensiasi meliputi semua kegiatan yang mengakibatkan suatu jenis magma induk yang semula relatif homogen terpecah-pecah menjadi beberapa bagian atau fraksi dengan komposisi yang berbeda-beda. Hal ini disebabkan karena migrasi ion atau molekul dalam larutan magma karena adanya perubahan temperatur dan tekanan. Yang pada akhirnya akan membentuk berbagai jenis batuan beku dengan komposisi yang berbeda-beda pula.
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Bowen reaction series
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DIAGRAM FASE
• Fase : padat, cair, gas
• Diagram fase : menggambarkan kondisi magma pada kondisi P & T tertentu
• Parameter penting dalam sistem magma : fase, komponen, variabel intensif
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DIAGRAM fASE
• fase : padat, cair• komponen : komponen terkecil yang
diperlukan utk pembentukan fase-fase
• dalam sistem (OH, H2O, MgO, NaAlSi3O8, dll)
•
• variabel intensif : temperatur dan tekanan, jumlah komponen
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DIAGRAM FASE
• Rumus fase : F = C – P + 2
• F : degree of freedom : jumlah kondisi minimum
• C : jumlah komponen;
• P : jumlah fase
• contoh utk air – es ------ C = 1 (H2O) ; P = 2 (es dan air)
• F = C – P + 2 ---- F = 1 – 2 + 2 = 1 (unary system)
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SISTEM 1 KOMPONEN
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SISTEM 2 KOMPONEN (BINER) DGN TITIK EUTEKTIK
h : titik eutektik; titik terendah fase cair ; kondisi terbentuknya 2 komponen
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SISTEM 2 KOMPONEN SOLID - SOLUTION
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SISTEM 2 KOMPONEN INCONGRUENT MELTING
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Why storage?
denser
stronger
crus
tcr
ust
Why do some magmas stall and pond in chambers during Why do some magmas stall and pond in chambers during ascent?ascent?
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Fractional Crystallization
http://www.geolsoc.org.uk/webdav/site/GSL/shared/images/geoscientist/Geoscientist%2019.2/7%20Volcano%20and%20magma%20chamber%20James%20Island2resized.jpg
Processes during storage in magma chambers
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http://www.geolsoc.org.uk/webdav/site/GSL/shared/images/geoscientist/Geoscientist%2019.2/7%20Volcano%20and%20magma%20chamber%20James%20Island2resized.jpg
Gravity settling
Processes during storage in magma chambers
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Gravity settling and cumulates
http://www.geol.lsu.edu/henry/Geology3041/lectures/12LayeredMafic/Fig12-15.jpg
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Buoyancy, sinking: Stoke’s Buoyancy, sinking: Stoke’s LawLaw
VV = the settling velocity (cm/sec)= the settling velocity (cm/sec)
gg = the acceleration due to gravity (980 cm/sec= the acceleration due to gravity (980 cm/sec22) )
r r = the = the radiusradius of a spherical particle (cm) of a spherical particle (cm)
ss = the density of the solid spherical particle = the density of the solid spherical particle
(g/cm(g/cm33))
ll = the density of the liquid (g/cm= the density of the liquid (g/cm33))
= the viscosity of the liquid (1 c/cm sec = 1 = the viscosity of the liquid (1 c/cm sec = 1 poise)poise)
V2gr ( )
9
2
s l
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Olivine in basaltOlivine in basalt
Olivine (Olivine (ss = 3.3 g/cm = 3.3 g/cm33, r = 0.1 cm) , r = 0.1 cm)
Basaltic liquid (Basaltic liquid (ll = 2.65 g/cm = 2.65 g/cm33, , = 1000 poise) = 1000 poise)
V = 2·980·0.1V = 2·980·0.12 2 (3.3-2.65)/9·1000 = 0.0013 cm/sec(3.3-2.65)/9·1000 = 0.0013 cm/sec
that’s ~1m per daythat’s ~1m per day
Sinking olivine in basaltSinking olivine in basalt
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Rhyolitic meltRhyolitic melt = 10= 1077 poise and poise and ll = 2.3 g/cm = 2.3 g/cm33
hornblende crystal (hornblende crystal (ss = 3.2 g/cm = 3.2 g/cm33, r = 0.1 cm) , r = 0.1 cm) V = 2 x 10V = 2 x 10-7-7 cm/sec, or 6 cm/year cm/sec, or 6 cm/year
feldspars (feldspars (ll = 2.7 g/cm = 2.7 g/cm33) ) V = 2 cm/yearV = 2 cm/year = 200 m in the 10= 200 m in the 1044 years that a stock might cool years that a stock might cool If 0.5 cm in radius (1 cm diameter) settle at 0.65 If 0.5 cm in radius (1 cm diameter) settle at 0.65
meters/year, or 6.5 km in 10meters/year, or 6.5 km in 1044 year cooling of stock year cooling of stock
Sinking x’tal in rhyoliteSinking x’tal in rhyolite
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IGNEOUS ROCKS CLASSIFICATION
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Ternary diagramsTernary diagrams
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Classification of Igneous Rocks
Figure 2-1a. Method #1 for plotting a point with the components: 70% X, 20% Y, and 10% Z on triangular diagrams. An Introduction to Igneous and Metamorphic Petrology, John Winter, Prentice Hall.
X
YZ
Incr
%X
Incr %Y Incr %Z
30 20 10
10
20
30
10
20
30%Z
20
10
30%X
A%Y
%Z
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Know how to classify a rockKnow how to classify a rock
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Volcanic rocks: aphanitic
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Ultra-mafic rocks & felsic vs. mafic
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Classification of Igneous Rocks
Figure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.
Plagioclase
OlivinePyroxene
Olivine gabbro
Plagioclase-bearing ultramafic rocks
90
(b)
Anorthosite
OlivineOlivine
ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene
LherzoliteLherzoliteH
arzb
urgi
te
Wehrlite
Websterite
OrthopyroxeniteOrthopyroxenite
ClinopyroxeniteClinopyroxenite
Olivine Websterite
PeridotitesPeridotites
PyroxenitesPyroxenites
90
40
10
10
DuniteDunite
(c)
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Classification of Igneous Rocks
Figure 2-4. A chemical classification of volcanics based on total alkalis vs. silica. After Le Bas et al. (1986) J. Petrol., 27, 745-750. Oxford University Press.
7773696561575349
52
Basalt
454137
45
Picro-basalt1
3
5
7
9
11
(Foid)ite
Phono-tephrite
13
Tephri-phonolite
Trachy-andesite
Phonolite
Trachyte
Basaltic trachy- andesite
Trachydacite
Trachy-basalt
BasalticAndesite
Andesite
Dacite
Rhyolite
TephriteBasanite
63ULTRABASIC BASIC INTERMEDIATE ACIDIC
wt% SiO2
Wt.
% N
a2O
+K
2O
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Classification of Igneous Rocks
Figure 2-5. Classification of the pyroclastic rocks. a. Based on type of material. After Pettijohn (1975) Sedimentary Rocks, Harper & Row, and Schmid (1981) Geology, 9, 40-43. b. Based on the size of the material. After Fisher (1966) Earth Sci. Rev., 1, 287-298.
Glass
Rock Fragments Crystals
VitricTuff
LithicTuff
CrystalTuff
(a)
Ash (< 2 mm)
Blocks and Bombs(> 64 mm)
LapilliTuff
Lapilli -TuffBreccia
TuffLapilli-stone
(b)
30 30
7070PyroclasticBreccia or
Agglomerate
Lapilli (2-64 mm)
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TEXTURES IN IGNEOUS ROCKS
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Textures: result of nucleation+growth
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Grain size
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Fast growth
a
Ocean Drilling ProgramOcean Drilling Program
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Crystal zoning
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Crystal shape
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Growth order
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Quartz - feldspar intergrowth
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Remelting
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Matrix texture
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Twinning
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Replacements
North CarolinaNorth CarolinaState UniversityState University Smith CollegeSmith College