Petrology Introduction to magma ang igneous roacks

8/12/2019 Petrology Introduction to magma ang igneous roacks

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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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Source: Partial Melting of ultramafic mantle at

Divergent Zones and Hot Spots


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Source: Partial Melting of mantle, ocean crust and continent at

Subduction Zones


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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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Porphyritic

Phenocrysts

Groundmass


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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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Documents

Petrology Introduction to magma ang igneous roacks