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GEOLOGICAL ENGINEERING MASTER PROGRAM
GADJAH MADA UNIVERSITY
PETROLOGI TERAPAN
(TKG 712, 2 SKS)Semester I Th. 2013/2014
Team Teaching:
Dr. Lucas Donny Setijadji
Dr. I Wayan Warmada
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References:
1. Winter, J.D. (2001) An Introduction
to Igneous and Metamorphic
Petrology, Prentice Hall, 697 p.
2. Wilson, M. (1989) Igneous
Petrogenesis: A Global Tectonic
Approach, Springer, 466 p.
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GEOLOGICAL ENGINEERING MASTER PROGRAM
GADJAH MADA UNIVERSITY
Chapter 2
Magma and Igneous Rocks
Dr. Lucas Donny SetijadjiDr. I Wayan Warmada
September 2013
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Internal structures of Earth:
- Lithosphere
- Asthenosphere- Mesosphere
- Core
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Interior of the Earth
EarthEarthss
InteriorInterior
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Formation of Igneous Rocks
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Scheme of
magmatism
and volcanism
(Schmincke,2004)
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Magma
MagmaA silicate molten rock inside the earth, formed bypartialmeltingof itsparental rocks inside the earths mantle or,in lesser amount in the lower crust. Magma has a mobile
nature, and it can contain restite of parental rocks(xenolith), or surviving crystals (xenocryst) and crystalsformed by solidifying magma
Lava
Magma that reaches the earth surface
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Locations of Magma Formation
(Schmincke, 2004)
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3 model offormation ofbasalticmagmas frompartial meltingof peridotite(Schmincke,2004)
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Magmatism is driven by addition of water
released by subducted slab
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Magmatism is driven by pressure drop
(decompression melting) at mid oceanic ridge (MOR)
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Magma Source: Partial Melting
Mineral
Hypothetical Solid Rock:
Intermediate Composition
A (Mafic)
B (Int)
C (Felsic)
Melting
Temp
1200C
1000C
800C
Temperature = 500C
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Magma Source : Partial Melting
Mineral
A (Mafic)
B (Int)
C (Felsic)
Melting
Temp
1200C
1000C
800C
Temperature = 900C Magma
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Mineral
A (Mafic)
B (Int)
C (Felsic)
Melting
Temp
1200C
1000C
800C
Temperature = 900C
Magma
Magma Separates Felsic
Remaining Rock: More Mafic
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Bottom Line on Partial Melting
Partial Meltingproduces a magmathat ismore felsicthan the parent rock
RockUltramafic
Mafic
Intermediate
Felsic
Magma from Partial MeltingMafic
Intermediate
Felsic
(more) Felsic
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Composition: Magma Source
Mafic Intermediate Felsic
Source: Partial Melting of ultramafic mantle at
Divergent Zones and
Ultramafic mantle
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Composition: Magma Source
Mafic Intermediate Felsic
Source: Partial Melting of ultramafic mantle at
Divergent Zones and Hot Spots
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Composition: Magma Source
Mafic Intermediate Felsic
Source: Partial Melting of mantle, ocean crust and continent at
Subduction Zones
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Composition: Magma Source
Mafic Intermediate Felsic
Source: Partial melting felsic continent above
Hot Spots & Subduction Zones
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Magma
Rises
and Cools
Magma
Chamber
Surface
Intrusive
(Plutonic)
Extrusive
(Volcanic)
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Bowens reaction series
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Palisades Intrusion
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Assimilation and magma mixing
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Igneous Environments
Extrusive Igneous Rock. Produced when lava erupts onto the surface.
The lava freezes on exposure to air or water.
Crystal grains lack time for growth and are mostly
invisible. Intrusive Igneous Rock.
Produced by the crystallization of magma while still
underground.
The magma freezes because of the gradual loss ofheat to the country rock.
Crystal grains have time to grow and are mostly
visible.
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Intrusive and Extrusive
Fine
Grained
Coarse
Grained
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Igneous Rocks
Intrusive Batholith Stock
Lopolith
Laccolith
Volcanic
neck Sill
Dike
Extrusive Lava flow or
plateau
Volcano(many types)
Crater
Caldera
Fissure
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Schematic block diagram of some intrusive bodies
T f I C t t ith S di
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Types of Igneous Contacts with Surrounding
Rocks
Contacts (boundary
between two rock bodies)
can be:
Concordant
Does not cross cut country
rock (surrounding rock)
structure, bedding, or
metamorphic fabric
Ex: laccolith, sill
Discordant Cross cuts country rock
structure
Ex: dike, batholith, stock
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Extrusive Igneous Structures
Volcano:
Anywhere material reaches earths surface
E t i I St t
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Extrusive Igneous Structures:
Scale
Large scale structures Lava plateau (LIP; flood basalt)
Ignimbrite (ash flow tuff;pyroclastic sheet)
Intermediate scale structures
Shield volcano Composite volcano
(stratovolcano)
Caldera, crater
Lava flow or dome
Small scale structures Tephra (pyroclastic material)
Lava flow features
Cinder cone
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Types of Igneous Rock
Geologists divide igneous rocks into two main
categories:
Volcanic(or extrusive) rocks cool from lava
eruptions and tend to have a f ine-grained texture.
Plutonic(or intrusive) rocks solidify undergroundand tend to have a coarse-grained texture.
Fine-grained Coarse-grained
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Igneous Composition
Mafic
Felsic
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Igneous
Rocks
Textures
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Textural classification ofigneous rocks
Phaneritic: crystals visible with naked eye
Plutonic orintrusive rocks
Aphanitic: crystal too small for naked eyeVolcanic orextrusive rocks
Porphyritic:two different, dominant grain sizes
Large xtals =phenocrysts; small xtals =groundmass
Fragmental: composed of disagregated igneous material
Pyroclastic rocks
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Porphyritic Size Distribution
Porphyritic -bimodal size distribution, withlarge grains surrounded by numerous smallgrains or glass
Phenocrysts -Large crystals formed byrelatively slow cooling below the earthssurface
Groundmass - Small crystals or glass, formedby more rapid cooling
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Textural classification ofigneous rocks
Pegmatitic: very large xtals (cm to 10s of cm); i.e.,slowlycooled
Forms veins or layers within plutonic body
Glassy: non-crystalline; cools very fast (e.g., obsidian)
Volcanic rocks
Vesicular:vesicles (holes, pores, cavities) form as gases expand
Volcanic rocks
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Igneous Minerals
Mineral Properties
Olivine Green to yellow-green; vitreous; fractures;small, equidimensional grains
Plagioclase Usually w hite or gray;
2 cleavages at 90;
elongate grains; striations sometimes visible
Pyroxene Greenish black or brownish black;
rather dull luster;
blocky grains
Amphibole Black with shiny, splintery appearance;two cleavages at 60 and 120;
elongate grains
Biotite Shiny, black sheets;
one perfect cleavage
Orthoclase Usually white or pink;
2 cleavages at 90;equidimensional grains
Muscovite Shiny, silvery sheets;one perfect cleavage
Quartz Colorless to gray;
vitreous with c onchoidalfracture;
irregular grains in intrusive rocks;
equidimensional phenocrysts in extrusive rocks
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Compositional terms forigneous rocks
Felsic:feldspar +silica~55-70% silica, K-feldspar > 1/3 of feldspars present
light-colored silicate mineralsContinental crust
Intermediate: between felsic and mafic
~55-65% silica, plag > 2/3 of feldspars present
Na-rich plag predominates over Ca-rich plag
Mafic: magnesium +ferric iron
~45-50% silica; Ca-rich plag dominant feldspardark silicate mineralsOceanic crust
Ultramafic: >90% mafic minerals, silica < 45%, few or no feldspars
Mantle-derived
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Igneous Textures - Crystalline
Coarse Grained Fine Grained
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Igneous Textures - Crystalline
Porphyritic
Phenocrysts
Groundmass
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Igneous Textures - Crystalline
Glassy
Vesicular
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Igneous Textures - Pyroclastic/Fragmental
Made of rock fragments
rather than crystals
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Igneous
Rocks
Classification
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Has the rock pyroclastic features?
[NO]YES=>
Use pyroclastic rock
classification
Carbonates > 50 %?
[NO]YES=> Use carbonatite classification
see classification for melilitic, kalsilitic,
leucitic rocks and kimberlites, lamproites and
lamprophyres
[NO]
=> =>Flow chart for melilitic, kalsilitic,
leucitic rocks... and lamprophyres
Is it charnockitic?
[NO]YES=> Use charnockite classification
Is it plutonic? YES=>
[NO]
M < 90 %? YES=>
[NO] =>
Use plutonic QAPF
Use ultramafic classification
Is it volcanic? YES=>Mode possible? YES=>
[NO]
Usevolcanic QAPF
Is it high-Mg? YES=>
[NO]Use high-Mg classification
If you get to this point, either the rock is not
igneous or you have made a serious mistake.
_____=>____
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IUGS Classification for Mafic and Ultramafic Igneous Rocks
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A classification of the phaneritic igneous rocks.
b.Gabbroic rocks. c.Ultramafic rocks. After
IUGS.
Plagioclase
OlivinePyroxene
Gabbro
Tro
ctoliteOlivine
gabbro
Plagioclase-bearing ultramafic rocks
90
(b)
Anorthosite
Olivine
ClinopyroxeneOrthopyroxene
Lherzolite
Websterite
Orthopyroxenite
Clinopyroxenite
Olivine Websterite
Peridotites
Pyroxenites
90
40
10
10
Dunite
(c)
Batuan Mafik
(Gabbroit)
Batuan Ultramafik
IUGS Classification for Mafic and Ultramafic Igneous Rocks
Q
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A classification and nomenclature of volcanic
rocks. After IUGS.
(foid)-bearing Trachyte
(foid)-bearing Latite
(foid)-bearingAndesite/Basalt
(Foid)ites
10
60 60
35 65
10
20 20
60 60
F
A P
Rhyolite Dacite
Trachyte Latite Andesite/Basalt
Phonolite Tephrite
3.A. Classification for VolcanicRocks based on minerals byIUGS (Streckeisen, 1976)
3.B. TAS (Total Alkali Silica) classification based on chemical
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composition for Volcanic Rocks
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.
Igneous Rocks Classification
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Igneous Rocks Classification
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Igneous Rocks
GraniteDioriteGabbro
RhyoliteAndesiteBasalt Dacite
GranodioriteMafic Intermediate Felsic
Fine
Co
arse
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Examples of Igneous Rocks
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Intrusive Rocks (Plutonic)
Dioriteis a coarse-grained, intrusive igneous rock thatcontains a mixture of feldspar, pyroxene, hornblendeand sometimes quartz. The specimen shown above isabout two inches (five centimeters) across.
Graniteis a coarse-grained, light colored, intrusive igneous rockthat contains mainly quartz and feldspar minerals. Thespecimen above is about two inches (five centimeters) across.
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Gabbro : is a coarse-grained, dark colored, intrusiveigneous rock that contains feldspar, augite and sometimesolivine. The specimen shown above is about two inches(five centimeters) across.
Peridotite : is a coarse-grained intrusive igneous rock that iscomposed almost entirely of olivine. It may contain small amountsof amphibole, feldspar, quartz or pyroxene. The specimen shownabove is about two inches (five centimeters) across.
Intrusive Rocks (Plutonic)
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Acid, late phase intrusive rocks
Pegmatite : is a light-colored, extremely coarse-grained intrusiveigneous rock. It forms near the margins of a magma chamber duringthe final phases of magma chamber crystallization. It often containsrare minerals that are not found in other parts of the magmachamber. The specimen shown above is about two inches (fivecentimeters) across.
Aplite:very fine-grained, white, grey or pinkish intrusive rockdominated by quartz and feldspar. Dykes of aplite are
commonly observed traversing granitic bodies.
Granite
Aplite
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Intrusive Rock
Syenite:coarse-grained intrusive igneous rock of the
same general composition as granite but lack in quartz.Feldspar is dominated by orthoclase
Monzonite:intrusive rock with approximately
equal amounts of plagioclase and alkali feldspar,with less than 5% quartz by weight.
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Granodiorite
Granodiorite: intrusive igneous rock similar to granite,but containing more plagioclase than orthoclase-typefeldspar. It usually contains abundant biotite mica andhornblende, giving it a darker appearance than truegranite.
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TonaliteTonalite:intrusive rock of felsic composition, phaneritic
texture, contains plagioclase (typically oligoclase or andesine)with 10% or less alkali feldspar. Quartz is present as more
than 20% of the rock. Amphiboles and pyroxenes are common
accessory minerals.
In older references tonalite is sometimes used as a synonym
for quartz diorite. However the current IUGS classificationdefines tonalite as having greater than 20% quartz and quartz
diorite with from 5 to 20% quartz.
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Ultramafic Intrusive Rocks
Dunite : ultramafic plutonic rock, phaneritic texture, withcomposition is > 90% olivine, with minor amounts ofother minerals such as pyroxene.
Peridotite : coarse-grained ultramafic igneousrock, consisting mostly of olivine and pyroxene.
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Ultramafic Intrusive Rocks
Pyroxenite : ultramafic igneous rock consisting essentially ofminerals of the pyroxene group, such as augite and diopside,
hypersthene, bronzite or enstatite.
Hornblendite: rare ultramafic plutonic rock consisting
mainly of the amphibole hornblende.
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Anorthosite:phaneritic, intrusive ultramafic igneous rock
characterized by a predominance of calcium-rich plagioclasefeldspar (90100%), and a minimal mafic component (010%) suchas pyroxene, ilmenite, magnetite, and olivine.
Carbonatites: intrusive or extrusive igneousrocks defined by mineralogic composition of >
50 % carbonate minerals.
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Volcanic Rocks
Diabase / dolerite: a mafic, holocrystalline, subvolcanic
rock equivalent to volcanic basalt or plutonic gabbro;dominated by plagioclase and pyroxene.
Andesite: is a fine-grained, extrusive igneous rock composed
mainly of plagioclase with other minerals such as hornblende,
pyroxene and biotite. The specimen shown is about two inches
(five centimeters) across.
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Volcanic Rocks
Rhyolite: light-colored, fine-grained, felsicextrusive igneous rock that typically containsquartz and feldspar minerals.
Obsidian: extrusive igneous rock of intermediate-acid
composition, forms when magma cools so rapidly that atoms
are unable to arrange themselves into a crystalline structure.The result is a volcanic glass with a smooth uniform texture that
breaks with a conchoidal fracture.
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Volcanic Rocks
Pumice: light-colored vesicular igneous rock, forms
through very rapid solidification of acid-intermediate
magma. The vesicular texture is a result of gas
trapped in the melt at the time of solidification.
Scoria : dark-colored igneous rock with abundant
round cavities known as vesicles. It ranges in color
from black or dark gray to deep reddish brown.Scoria usually has a composition basalt, but can also
andesite.
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Volcanic Rocks
Basalt: dark-colored, fine-grained, mafic igneous rock
composed mainly of plagioclase and pyroxene minerals.It most commonly forms as an extrusive rock, such as alava flow, but can also form in small intrusive bodies,such as an igneous dike or a thin sill.
Komatiite: ultramafic volcanic rock with low
silicon, potassium and aluminium, and high to
extremely high magnesium content.
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Feldspatoid Igneous Rocks
Nepheline-bearing rock Leucite-bearing rock
Feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a
different structure and much lower silica content. They occur in rare and unusual types of
igneous rocks, both intrusive and vulcanic.
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