Continued intro & classification

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52

Basalt

454137

45

Picro-basalt1

3

5

7

9

11

(Foid)itePhono-tephrite

13Tephri-phonolite

Trachy-andesite

Phonolite

Trachyte

Basaltic trachy- andesite

Trachydacite

Trachy-basalt

BasalticAndesite

Andesite

Dacite

Rhyolite

TephriteBasanite

63ULTRABASIC BASIC INTERMEDIATE ACIDIC

wt% SiO2

Wt.% Na

2O+K

2O

Updates

•Lab starts this week•Monday 9.30-12.20 lab, •Wednesday 2.30-5.30 lab

Today’s topics:1a. Heat, pressure and the geotherm1b. Geotherm and melting1c. Different ways to melt2. Classification of igneous rocks

The Pressure Gradient

• P increases = gh• Nearly linear through mantle

– ~ 30 MPa/km 1 GPa at base of ave

crust• Core: incr. more rapidly

since alloy more dense

1010 2020 303000

10001000

20002000

30003000

40004000

50005000

60006000D

epth

(km

)D

epth

(km

)

Pressure (GPa)Pressure (GPa)4040

Mantle

Core

Figure 1-8. Pressure variation with depth. From Dziewonski and Anderson (1981). Phys. Earth Planet. Int., 25, 297-356. © Elsevier Science.

Heat

Heat Sources Heat Sources in the Earthin the Earth

The Geothermal GradientCrust

Mantle

OuterCore

Temperature(K)

0 5 10

1000

2000

3000

4000

5000

6000

Dep

th (k

m) S waves

P waves

InnerCore

Lithosphere

Astheno-sphere

Solid

Liquid

Meso-sphere

S waves

Rocks at different depth: change in P & T: Phase

changeT T

P P

Atoms have a “choice” as to how they want to arrange

themselves in a phase

Plate Tectonic - Igneous Genesis

? ???

600 km

400

200 kmContinental CrustOceanic CrustLithospheric MantleSub-lithospheric Mantle

Source of Melts

15 3 46 7 2

Geotherm and solidus: how to melt

Processes That Form Magma

Processes that form magma and rock

Environments of Magma Formation

Environments of Magma Formation

Environments of Magma Formation

Environments of Magma Formation

Environments of Magma Formation

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)

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

YZIncr %X

Incr %Y

Incr %Z

30 20 10

10

2030

10

20

30%Z

20

10

30%X

A%Y

%Z

Classification of Igneous Rocks

Figure 2-1b. Method #2 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.

Y

X

Z

70

67

A

100

0

%X

Classification of Igneous RocksFigure 2-2. A classification of the phaneritic igneous rocks. b. Gabbroic rocks. c. Ultramafic rocks. After IUGS.

Plagioclase

OlivinePyroxene

Gabbro

Troctolite

Olivine gabbro

Plagioclase-bearing ultramafic rocks

90

(b)

Anorthosite

OlivineOlivine

ClinopyroxeneClinopyroxeneOrthopyroxeneOrthopyroxene

LherzoliteLherzoliteHa

rzbu

rgite

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)itePhono-tephrite

13Tephri-phonolite

Trachy-andesite

Phonolite

Trachyte

Basaltic trachy- andesite

Trachydacite

Trachy-basalt

BasalticAndesite

Andesite

Dacite

Rhyolite

TephriteBasanite

63ULTRABASIC BASIC INTERMEDIATE ACIDIC

wt% SiO2

Wt.% Na

2O+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

Tuff Lapilli-stone

(b)

30 30

7070PyroclasticBreccia or

Agglomerate

Lapilli (2-64 mm)