Chapter 4:
Igneous Rocks
 Add section detail briefings
Classification of Igneous Rocks
Pyroclasts
Extrusive rocks
Porphyry
Intrusive rocks
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Porphyry
Intrusive rocks
Bomb
Pumice
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Porphyry
Intrusive rocks
Bomb
Pumice
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Porphyry
Intrusive rocks
Bomb
Mafic
Basalt
Pumice
Felsic
Rhyolite
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Porphyry
Intrusive rocks
Bomb
Mafic
Basalt
Pumice
Felsic
Rhyolite
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Extrusive igneous
rocks cool rapidly
and are finegrained.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Bomb
Pumice
Mafic
Basalt
Felsic
Rhyolite
Gabbro
Granite
Porphyry
Intrusive rocks
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Extrusive igneous
rocks cool rapidly
and are finegrained.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Bomb
Pumice
Mafic
Basalt
Felsic
Rhyolite
Gabbro
Granite
Porphyry
Intrusive rocks
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Extrusive igneous
rocks cool rapidly
and are finegrained.
Intrusive igneous
rocks cool slowly,
allowing large,
coarse crystals to
form.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Bomb
Pumice
Mafic
Basalt
Felsic
Rhyolite
Gabbro
Granite
Porphyry
Intrusive rocks
Phenocrysts
Porphyry
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Extrusive igneous
rocks cool rapidly
and are finegrained.
Intrusive igneous
rocks cool slowly,
allowing large,
coarse crystals to
form.
Intrusive (plutonic)—Extrusive (volcanic)
Pyroclasts
Volcanic ash
Extrusive rocks
Bomb
Pumice
Mafic
Basalt
Felsic
Rhyolite
Gabbro
Granite
Porphyry
Intrusive rocks
Phenocrysts
Porphyry
Extrusive pyroclasts
form in violent
eruptions from lava
in the air.
Extrusive igneous
rocks cool rapidly
and are finegrained.
Intrusive igneous
rocks cool slowly,
allowing large,
coarse crystals to
form.
Some intrusive
porphyritic crystals
grow large, but the
remaining melt
cools faster,
forming smaller
crystals.
The common rock forming minerals in the
earth’s crust are made from just 8 elements.
NORMAN L. BOWEN (1887-1956)
Queen’s, MIT and Geophysical Laboratory at the Carnegie Institute of Washington
•
•
Pioneering work at the interface between geology with physical chemistry
Studied the formation of igneous rocks in the laboratory
April 29, 1948
Dear Professor Gilluly:
Having had occasion some years ago to learn the art of lipreading I noticed
yesterday when I was giving may paper that at the end of each of my sentences
you said, "Horse shit". Evidently you had made special note of the word
"equilibria" in the title of my paper and were from time to time reminding yourself
and your neighbors of the gist of the discussion. You are, however, under a
misapprehension as to the derivation of the word "equilibria". It does not come
from equus = a horse and libria = things liberated or discharged, but is from
quite different roots. If you will consult a chemist you will be able to learn the real
significance of the word and I may add that I feel that one so highly placed in
geological circles as you should make it a point to acquire some familiarity with
the exact significance of common terms used in collateral sciences.
Trusting that you will not resent my correction and suggestions, I am
Yours sincerely,
Norman L. B
BOWEN’S REACTION SERIES
Magma
composition
Temperature
~600°C
Orthoclase feldspar
Felsic,
Rhyolitic
(high silica)
Muscovite mica
Quartz
Biotite
mica
Sodiumrich
Intermediate,
andesitic
Amphibole
Pyroxene
~1200°C
Olivine
Simultaneous
crystallization
Calciumrich
Mafic,
basaltic
Ultramafic
(low silica)
BOWEN’S REACTION SERIES
As magma temperature
decreases…
…materials
crystallize
in an
Temperature
ordered
~600°C
series…
…while plagioclase feldspar
crystallizes, from calciumMagma
rich sodium-rich form…
composition
Orthoclase feldspar
Felsic,
Rhyolitic
(high silica)
Muscovite mica
Quartz
Biotite
mica
Sodiumrich
Intermediate,
andesitic
Amphibole
Pyroxene
~1200°C
Olivine
Simultaneous
crystallization
Calciumrich
…and the composition
of magma changes from
ultramafic to andesitic.
Mafic,
basaltic
Ultramafic
(low silica)
The composition of tin-lead solder is adjusted to the ‘eutectic’
in order to achieve melting at the lowest temperature
An important tin/lead solder is 63/37, called “eutectic,” meaning
it goes directly from solid to liquid without a partially molten
stage. This alloy melts at 361°F (183°C), the lowest melting
point of any tin-lead alloy. Other eutectic solders include
62.5% tin, 36.1% lead
and 1.4% silver (354°F,
179°C)
96% tin and 4% silver
(430°F, 221°C);
97.5% lead and 2.5%
silver (581°F, 305°C)
0.75% tin, 97.5 % lead
and 1.75% silver
(590°F, 310°C).
(590°F, 31
Physical properties of melting and crystallization Binary eutectic
Fractional crystallization:
Basaltic intrusion
245–275 m (800–900 ft)
Sandstone
Basalt
Mostly sodium-rich
plagioclase feldspar;
no olivine
Calcium-rich
plagioclase feldspar
and pyroxene;
no olivine
Olivine
Basalt
Sandstone
Basalt cooled quickly at
the edges of the intrusion.
Fractional crystallization:
Olivine
crystallizes
first
Pyroxene and
plagioclase
feldspar
crystallize
A gradient of
pyroxene and
feldspar is
established.
Plagioclase
feldspar
continues to
crystallize.
Complex petrogenetic histories begin with Partial Melting:
Partial melting creates
a magma of a particular
composition.
Crystallizing
minerals
Blobs of melt
(solidified)
in a rock
(migmatite)
Magma
chamber A
Magma
chamber B
Partial melting
of country rock
Basaltic
magma
…more fractional crystallization
Partial melting creates
a magma of a particular
composition.
Cooling causes minerals
to crystallize and settle.
Crystallizing
minerals
Magma
chamber A
Magma
chamber A
Magma
chamber B
Partial melting
of country rock
A basaltic magma
chamber breaks
through. Mixing results
Basaltic
magma
Magma mixing
in andesitic
magma.
Magma
chamber B
Crystals may
accumulate on
the sides and
roof of the
chamber due
to turbulence.
Lava flow
Country
rock
Ash falls and pyroclasts
Volcano
Volcanic neck with
radiating dikes
Stock
Sill
Sill
Sill
Dikes cut
across layers
of country
rock…
…but sills run
parallel to them.
Batholiths are the largest
forms of plutons, covering
at least 100 km2.
Assimilation of country rock
Rising magma
wedges open
overlying country
rock.
The magma melts
the surrounding
rock...
…which changes
the magma’s
composition.
Country
rock
The magma also
breaks off xenoliths
that sink into the
magma.
A sill runs parallel to country rock layers
Sill
A dike cuts across layers
Dike
Island arc volcanoes,
Java, Indonesia
Intermediate
ISLAND ARC
PLATE SUBDUCTION
Island arc
volcano
Mafic to intermediate
intrusives (plutonism)
Mafic to intermediate
extrusives (volcanism)
Subduction zone
Oceanic
lithosphere
Plate divergence boundary,
Mid-Atlantic Ridge, Iceland
Mafic
PLATE
DIVERGENCE
Mid-ocean ridge
Basatic extrusives
Basaltic intrusives
Partial melting
Of upper mantle
Rising magma
Hot-spot volcano,
Volcanoes National Park, Hawaii
Mafic
HOT-SPOT
VOLCANISM
Hot-spot volcano
Basatic extrusives
Basaltic intrusives
Mantle plume
(hot spot)
Mantle
Continental margin volcano,
Mt. Rainier, Washington
HOT-SPOT
VOLCANISM
Mafic to felsic intrusives
Mafic to felsic extrusives
Subduction
zone
Intermediate
to
Felsic
Continental
margin volcano
Mafic
Sediment layers
OPHIOLITE
SUITE
Deep-sea
sediments
Pillow basalts
Pillow basalt
Sheeted dike
complex
Dikes
Thin section of gabbro
Gabbro
Peridotites and
other ultramafic
rocks
Thin section of peridotite
Hot mantle rises,
decompresses,
and melts.
Dikes
A thin dike erupts,
spilling lava in
“pillows.”
Pillow lava
Newer, thinner
sediments
Older, thicker
sediments
Sheeted dikes
in basalt
Oceanic
crust
Gabbro
Moho
Peridotite layer
Mantle
Cold
seawater
Sheeted
dikes
Seawater filters
through the
basalt layer,
where it is heated.
Spreading
center
Heated
seawater
carrying
dissolved
minerals
Mantle
The heated seawater
then rises. Dissolved
minerals precipitate in
the ocean.
Dikes intruding dikes
Dikes intrude
dikes to form
sheeted dikes.
Sediments are
deposited on
the spreading
seafloor.
The gabbro layer
metamorphoses
by contact with
the magma.
Magma chamber
Peridotite layer
Crystals settle out
of the magma,
forming the
peridotite layer.
Intermediate
Magma of intermediate
composition is erupted
to form arc volcanoes.
Molten sediments
combine with
lithospheric magma.
Trench
Oceanic sediments
Oceanic crust basalt
Oceanic mantle
lithosphere
Magma chamber
The water
and molten
sediments melt
parts of the
overlying plate.
Asthenosphere
Subducting oceanic crust
carries sediments with it.
H2O
H2O
H2O
Water remains trapped
as the pressure and
temperature increase.
Sediment
grains
Water
The trapped water is
released as the
temperature increases,…
…causing the
sedimentary
rocks to melt
at lower
temperatures.