Magma, Rocks Classification & Textures

MAGMA

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)

JENIS KONVERGEN

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

Environments of Magma Formation

Environments of Magma Formation

Stages in ascent

• EruptionEruption

• (Fragmentation)(Fragmentation)

• VesiculationVesiculation

• Renewed ascent Renewed ascent

• StorageStorage

– mixingmixing

– assimilationassimilation

– crystallizationcrystallization

• Buoyant ascentBuoyant ascent

• Partial meltingPartial melting

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)

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

Partial Melting: The Origin of Basalt and Granite

Asthenosphere40% Silica

Melting

Basaltic magma = 50% silica (1100o C)

Forms the rock basalt

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)

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.

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.

Bowen reaction series

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

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

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)

SISTEM 1 KOMPONEN

SISTEM 2 KOMPONEN (BINER) DGN TITIK EUTEKTIK

h : titik eutektik; titik terendah fase cair ; kondisi terbentuknya 2 komponen

SISTEM 2 KOMPONEN SOLID - SOLUTION

SISTEM 2 KOMPONEN INCONGRUENT MELTING

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?

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

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

Gravity settling and cumulates

http://www.geol.lsu.edu/henry/Geology3041/lectures/12LayeredMafic/Fig12-15.jpg

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

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

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

IGNEOUS ROCKS CLASSIFICATION

Ternary diagramsTernary diagrams

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

Know how to classify a rockKnow how to classify a rock

Volcanic rocks: aphanitic

Ultra-mafic rocks & felsic vs. mafic

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)

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

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)

TEXTURES IN IGNEOUS ROCKS

Textures: result of nucleation+growth

Grain size

Fast growth

a

Ocean Drilling ProgramOcean Drilling Program

Crystal zoning

Crystal shape

Growth order

Quartz - feldspar intergrowth

Remelting

Matrix texture

Twinning

Replacements

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