lecture 4b igneous rocks i - west virginia...

Lecture 4b

Igneous Rocks I

Objectives• Discover Nature of

Minerals that Crystallize from Magma to Make Igneous Rocks.

• Learn About Processes that Create the Great Variety of Igneous Rocks.

Objectives (continued)

• See How Minerals and Process Lead to IgneousRock Classification

• Introduce Volcanoes

RockRock•• SOLID COHESIVE SOLID COHESIVE

AGGREGATE OF AGGREGATE OF GRAINS OF ONE GRAINS OF ONE

OR MORE OR MORE MINERALS.MINERALS.

Igneous Rock

=Rock Congealed from Magma Magma = Molten Rock Lava = Magma at the Surface

Rock Cycle

Geothermal Gradient

16.5oC/km 48oF/mi

Geothermal Gradient

• How Far Down To Melt Quartz (570oC)? 570oC/16.5oC/km = 34 km (~20 mi)

Geothermal Gradient

• How Far Down To Melt Olivine (1500oC)? 1500oC/16.5oC/km = 90 km (~55 mi)

Geothermal Gradient

• 30-90 km Depth = Hot Enough To Melt Rocks

• Magma Chambers

What's in a Magma Chamber?

• Most Are Similar. • Magma Rich in Fe, Mg, Ca,

(SiO4)-4 = Mafic• Little Na, K• Aqueous Solutions of S,

Gasses ( CO2, SO2, etc. )

Most Igneous Rocks Have Compositions Very Different

from Magma Chambers• How Does the Earth Create

a Wide Variety of IgneousRock from Similar BoringMagma Chambers?

• How Would You Try To Answer the Question?

Time Out for

Discussion

N.L. Bowen

• Worked in Experimental Petrology on Early 1900s

Norman Bowen and Fiancee, Mary Lamont, ~1911

http://geoclio.st.usm.edu/bowen3.jpg

“Bomb” Xlization Studies

• High “Temp.” Ovens • Up to 1500oC (< 2700oF)• "Reaction" Series of

Silicate Minerals

Bowen’s Reaction Series

• Unless Isolated From Magma, First Xls Reactwith Magma to Form New Xls of New Minerals.

Bowen’s Reaction Series

See Figure 3.20 on p. 73 in 11th edition of Plummer et al.

Hi

Lo

Tem

p.

Bowen’s Reaction Series• If First Xls are in Equilibrium

with Magma,• then Igneous Rocks have

same Chemistry & Mineralogy as BoringMagma Chambers

• No Help to Answering Question!

So, How Do We Get Variety?

• Nature Must Isolate the First-Formed Xls from the Magma

• How? Several Ways

How Does Nature Isolate Xls?

• Zoned Xls–Ca-100 Plagioclase to –Na-100 Plagioclase

Zoned Xl of “Plag”• Magma Composition =

Plagioclase Feldspar with Equal % of Sodium & Calcium(Na50-Ca50)

Zoned Xl of “Plag”

• Ca100 Plagioclase Forms First

Ca100

Magma is Depleted in Ca++

Ions as Xl Grows


• Ca75Na25 Plagioclase Forms

Ca100

Ca75Na25

Magma is More Depleted in Ca++ Ions & Relatively Enriched in Na+ Ionsas Xl Grows


• Ca30Na70 Plagioclase Forms

Magma is EvenMore Depleted in Ca++ Ions & Relatively Enriched in Na+ Ionsas Xl Grows

Ca100

Ca75Na25

Ca30Na70


• Na100 Plagioclase Forms Last

Magma has LostAll Ca++ Ions, So Only Na+ Ions AreAvailable for Xl Growth

Ca100Ca100

Ca75Na25

Ca30Na70

Na100


• Gravity Settling–Olivine settling

out of “lighter”mafic magma

Olivine image from www.webmineral.com


• Filter Pressing • Like Squeezing Water

(Magma) from a Sponge (Xls)

Fractionation = Fractional Xlization

High FeMagma

Fe RichXls

ReducedFe Magma

Mafic UltramaficFelsic

Fractional Xlization

ReducedFe Magma

Mafic UltramaficFelsic

Low FeMagma

High FeXls

Fe RichXls

Fractional XlizationMafic UltramaficFelsic

Low FeMagma

Low FeMagmaReduced

Fe Xls

Low FeXls

High FeXls Fe Rich

Xls

Igneous Rock Classification Mineral Composition

(Magma History)

Text

ure

(Coo

ling

His

tory

)

MAFIC FELSICINTERMEDIATE

Most Important Igneous Rocks

Mineral Composition

Text

ure

Felsic Mafic Ultra-Mafic

Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice

rhyoliteporphyry

andesiteporphyry

basaltporphyry

basalt

granite

andesiteporphyry

obsidian

Igneous Rock Classification

Mineral Composition(Magma History)

Text

ure

(Coo

ling

His

tory

)

See Figure 3.20 on p. 73 in 11th edition of Plummer et al.



Text

ure

(Coo

ling

His

tory

)



Text

ure

(Coo

ling

His

tory

)

Igneous Rock Composition, 11th ed. Plummer, p. 62, Fig 3.6



Text

ure

(Coo

ling

His

tory

)

Texture & Cooling History

• Very Rapid Cooling: No Xls = Glass or “Solid Bubbles”

•Rapid Cooling: Fine Xls•Slow Cooling: Coarse Xls - Can

Be Seen at Arm’s Length• Two-Stage Cooling (Slow, then

Rapid): Mix of Fine & Coarse Xls

Texture Terms• No Xls: Glassy or Cellular• Fine Grained Xls: Aphanitic• Coarse Grained Xls: Phaneritic• Mix of Coarse Xls (Phenocrysts)

& Fine Xls: Porphyritic

Texture & Environment

• Glassy or Cellular - Surface of Lava Flow

• Fine Grained Xls: Aphanitic -Shallow Depth

• Coarse Grained Xls: Phaneritic -Deep Beneath Surface

Texture & Environment - #2

Porphyritic Texture:• First, Magma Cooled Slowly at

Great Depth• Later, Magma Cooled Rapidly near

the Surface


Text

ure


Text

ure


Inter-mediate

Cellular,GlassyAphanitic

Phaneritic

Porphyry


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotiteperidotite

Peridotite

• Olivine-Rich Ultramafic Rock• Peridot = Gem Quality Olivine


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

basalt

gabbro

basalt

gabbro


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

basalt

gabbro

basalt

Gabbro


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

rhyolite

granite


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granitegranite

Granite is Used for TombstonesGranite is Used for Tombstones

U.S. GrantU.S. Grant R.I.P.R.I.P.

B. 1822B. 1822 D. 1885D. 1885


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

andesite

diorite


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

andesite

diorite


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice scoriapumiceobsidian


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice scoriapumiceobsidian


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice

rhyoliteporphyry

andesiteporphyry

basaltporphyry

rhyoliteporphyry

andesiteporphyry

basaltporphyry

obsidian


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice

rhyoliteporphyry

andesiteporphyry

basaltporphyry

rhyoliteporphyry

andesiteporphyry


Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice

rhyoliteporphyry

andesiteporphyry

basaltporphyry

Most Important Igneous Rocks

Mineral Composition

Text

ure


Inter-mediate

Cellular,GlassyFine

Coarse

Mix

rare

rare

rare

peridotite

basalt

gabbro

rhyolite

granite

andesite

diorite

scoriapumice

rhyoliteporphyry

andesiteporphyry

basaltporphyry

basalt

granite

andesiteporphyry

obsidian

Volcanoes:• Composition of Magma:

Important To Nature of Volcanic Eruptions and Resulting Landforms.

3 Eruption Types:

• Gaseous: Few Landforms

3 Eruption Types:

• Gaseous: Few Landforms• Explosive: Viscous Magma -

Rhyolitic or Andesite -Pyroclastics

Explosive Eruption: Mt. St.

Helens Pyroclastics

1980

3 Eruption Types:

• Gaseous: Few Landforms• Explosive: Viscous Magma -• Effusive: Fluid Magma -Basaltic - Lava

Fluid BasalticLava FlowMauna Loa, March 1983

Nyriagongo Volcano, Dem. Rep. of Congo

Vent Eruptions =True Volcanoes

USGS Map

//vulcan.wr.usgs.gov/Volcanoes/Africa/Maps/map_drcongo_volcanoes.htmlOther Map: Global Volcanism Program Volcanic Activity Reports

www.volcano.si.edu/gvp/volcano/region02/africa_c/nyamura/var.htm#2603

Map of eruption sites and lava flows at Nyiragongo and Nyamuragira's 1977 Murara vent. The location of the stippled flow on Nyiragongo was provided by M. Krafft. Courtesy of Y. Pottier.

Source of Next Images:

Nyriagongo Volcano

Goma

Nyiragongo

Volcano

Y. Pottier

Sources of Next 3 Images:http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyiragongo2.html

Mudende area with the Adventist University of Central Africa campus.

http://volcano.und.nodak.edu/vwdocs/volc_images/africa/nyiragongo.html

Lava Lake, Nyriagongo Volcano, 1994

Photo by J. Lockwood, USGS

Refugees near Nyriagongo Volcano, 1994

Photo by J. Lockwood, USGS

Source of Next 3 Images:

/www.cnn.com/2002/WORLD/africa/01/20/congo.eruption/index.html

Nyriagongo Volcano, Jan 2002

Nyriagongo Lava Flow into Lake Kiwa

Jan 2002

2 Types of Eruption Apertures:

•Fissures•Vents

Basaltic Fissure Eruption, Hawaii 1983

Popocatepetl, Mexico: 1994

Start Working on Test Questions are available on my web site

http://www.geo.wvu.edu/~kite/teaching.htm

Next Time: Bring “Magma Chamber”(Lava Lamp)

lecture 4b igneous rocks i - west virginia...

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