Transcript IGNEOUS ROCK - CoconinoHighSchool

IGNEOUS ROCK
Felsic rich
igneous lunar
rock collected
from the lunar
highlands of
the moon by
Apollo 16
astronauts.
Rock Classification
ROCKS
IGNEOUS
-most abundant
-primary rocks
-source is magma
or lava
SEDIMENTARY
-thin veener in Oceanic
and Continental
Crusts
-secondary rocks
METAMORPHIC
-proportion is similar to
that of Igneous
rocks
-change of forms of Ig.
And Sed. Due to
Temperature,
Pressure and
Chemical Fluids
Rock
Cycle
Origin: Igneous Rock
“Fire-formed rocks“ Crystallize from
molten material:
IGNEOUS ROCKS: The rocks formed through
volcanic action OR
The rocks which are derived from a molten mass
“magma or lava”
Magma – molten rock below the Earth's surface
Lava – molten rock that erupts onto the Earth's
surface through a volcano or crack (fissure)
Origin: Igneous Rock
VOLCANO: A gap in the Earth’s Crust where molten rocks
and other material escape onto the Earth’s surface
SOURCE OF IGNEOUS ROCKS:
Magma:
Molten mass comprising most abundant elements
in earth – Si, Al, Fe, Ca, Mg, K, H & O. Where
the SiO2 is most abundant amongst all.
Temperature of Magma- 10400 to 12000 C
Formation of Magma
How are rocks melted?
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1. Heating
2. Depressurization
3. Increase water content
4. Increased silica content
Where do rocks melt?
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Subduction zones
(Felsic and Intermediate)
Mantle Plumes (“Hot Spots”)
not only at
Divergent
Boundaries
Mafic
Hot and
High Pressure
Hot and
Low Pressure
Cooling Rates of Magma
Cooling rates influence the texture if the
igneous rock:
Quick cooling = fine grains
Slow cooling = coarse grains
Magma
Different magmas have different
viscosities. Viscosity is the property of
a substance to internally resist flow.
Example: Pine Sap or Molasses (High
Viscosity) vs. Water (Low Viscosity)
The HIGHER the viscosity, the more
resistance to flow!!
Igneous rocks are classified on
their texture and their composition.
Igneous textures:
Glassy
Aphanitic
Phaneritic
Porphyritic
Vesicular
Pyroclastic
Igneous rocks are classified on
their texture and their composition.
Igneous textures:
Glassy instantaneous
cooling
Obsidian =
volcanic glass
Igneous rocks are classified on
their texture and their composition.
Aphanitic - fine
grain size
(< 1 mm); result of
quick cooling
Basalt
Rhyolite
Andesite
Igneous rocks are classified on
their texture and their composition.
Phaneritic coarse grain size;
visible grains
(1-10 mm); result
of slow cooling
Granite
Diorite
Gabbro
Igneous rocks are classified on
their texture and their composition.
PorphyriticMixture of grain
sizes caused by
mixed cooling
history; slow
cooling first,
followed by a period
of somewhat faster
cooling.
Igneous rocks are classified on
their texture and their composition.
Vesicular contains tiny holes
called vesicles
which formed due
to gas bubbles in
the lava or magma.
Very porous. May
resemble a sponge.
Commonly low
density; may float
on water.
Igneous rocks are classified on
their texture and their composition.
Pyroclastic or
Fragmental pieces of rock and
ash come out of a
volcano and get
welded together by
heat.
Tuff - made of volcanic ash
Volcanic breccia - contains fragments of finegrained igneous rocks that are larger than ash.
BROAD CLASSIFICATION OF IGNEOUS ROCKS
Intermediate rocks
(Hypabyssal rocks)
Volcanic rocks
(Extrusive rocks)
-Lava or Magma
flows
-Pyroclastic flows
Plutonic rocks
(Intrusive rocks)
-dykes, sills,
batholiths,
laccoliths etc.
Igneous Rocks Are Subdivided Into Two Classes
•Volcanic (Extrusive)
Volcanic igneous rocks form at the earth's
surface as lava cools.
•Plutonic (Intrusive)
Plutonic igneous rocks form deep
underground where magma cools slowly.
Mineral Percentage
Igneous Rock Classification
Intrusive
(Plutonic)
Extrusive
(Volcanic)
Continental Crust
Oceanic
Crust
Mantle
Intrusive Igneous Rock
E.g., Felsic -Granite (Phaneritic):
Quartz
Biotite
Na Plagioclase
Crystallized (Solidified)
Felsic Magma
Poor in: Fe, Mg, Ca, (<20%)
Rich in: Silica (>70%)
Extrusive vs.
Intrusive
(Mafic Rocks)
Mafic Magmas
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Hot (>1000oC)
Non-Viscous (runny, flows
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“Dry” (no H2O or C02)
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easily)
Mafic Rocks
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Usually Extrusive, Fine-grained,
Mafic (Basalt) rock forms oceanic
crust, Shield Volcanoes and Basalt
Floods
If Intrusive, course-grained mafic rocks
are formed Gabbro.
If intrusive, Dikes and Sills more
common
Igneous Rock Classification
Intermediate
Mafic
Granite
Rhyolite
Diorite
Andesite
Gabbro
Basalt
Extrusive
Intrusive
Felsic
(Porphyritic)
Bowen’s Reaction Series
Minerals form as molten rock crystallizes. A generalized
order of crystallization of minerals is shown in the
Bowen's Reaction Series. As the magma cools, first
olivine, then pyroxene, then amphobole, etc. will be
crystallized (assuming the proper elements are
available).
Bowen's Reaction Series has two branches.
They are:
1.Discontinuous reaction series, from
olivine to biotite,.
2.Continuous reaction series, from Ca
plagioclase to Na plagioclase.
Felsic
Intermid
Mafic
KINDS OF IGNEOUS ROCK
Bowen’s Reaction Series
The discontinuous reaction series involves the darkcolored ferromagnesian minerals:
1.olivine
2.pyroxene
3.amphibole
4.biotite.
The continuous reaction series involves the plagioclase
feldspars. Plagioclase feldspars are an example of a "solid
solution series", exhibiting gradations in chemical and
physical properties. Chemically, this series consists of two
"end members":
1. Na plagioclase (NaAlSi3O8), the sodium "end
member", and
2. Ca plagioclase (CaAlSi2O8), the calcium "end
member".
BOWEN'S REACTION SERIES
Shows a generalized crystallization order of
minerals as a magma cools.
GENERALITIES down the reaction series
(from top to bottom):
Easier to melt minerals
The more complex the silicate mineral
Higher the viscosity of the magma
More resistant the mineral is to chemical
weathering
Lower the rock's final density
FLUIDITY OF MAGMA
Fluidity or Viscosity of magma depends on content (%)
of Silica
Silica Rich (felsic)
-known as Acidic magma
-More viscous, so do not
spreads and piles up at one
place (trap gas easily)
Silica poor (mafic)
-Known as Basic magma
-Less viscous, moves
faster and occupies
larger area (release gas
easily)
However, the viscosity of magma is considerably influenced by
temperature too. When temperature is less- magma is more viscous
(thicker) and when temperature is high - less viscous (thinner).
Volcanic Eruption of Magma
When magmas reach the surface of the
Earth they erupt from a vent. They may
erupt explosively or non-explosively.
Non-explosive eruptions are favored by low
gas content and low viscosity magmas
(basaltic to andesitic magmas).
Usually begin with fire fountains due to
release of dissolved gases
Produce lava flows on surface
Produce Pillow lavas if erupted beneath
water
Eruption of Magma
Explosive eruptions are favored by high gas content and high
viscosity (andesitic to rhyolitic magmas).
Expansion of gas bubbles is resisted by high viscosity of magma
- results in building of pressure
High pressure in gas bubbles causes the bubbles to burst when
reaching the low pressure at the Earth's surface.
Bursting of bubbles fragments the magma into pyroclasts and
tephra (ash).
Cloud of gas and tephra rises above volcano to produce an
eruption column that can rise up to 45 km into the
atmosphere.
Eruption of Magma
Tephra that falls from the eruption column produces a
tephra fall deposit.
Eruption of Magma
If eruption column
collapses a pyroclastic
flow may occur, wherein
gas and tephra rush down
the flanks of the volcano
at high speed. This is the
most dangerous type of
volcanic eruption. The
deposits that are produced
are called ignimbrites.
Eruption of
Magma
Lateral blasts and
debris avalanches
occur when gas is
released suddenly
by a large
landslide or debris
avalanche taking
out part of the
volcano
Plutons
Plutons = Igneous rocks cooled at
depth.
Name comes from Greek god of the
underworld - Pluto.
Pluton features
Dikes are small
(<20 m wide)
shallow intrusions
that show a
discordant
relationship to the
rocks in which they
intrude.
Discordant means that they cut across preexisting structures. They may
occur as isolated bodies or may occur as swarms of dikes emanating
from a large intrusive body at depth.
Pluton features
Sills are also small
(<50 m thick)
shallow intrusions
that show a
concordant
relationship with
the rocks that they
intrude. Sills
usually are fed by
dikes, but these
may not be
exposed in the
field.
Pluton features
Laccoliths are
somewhat large
intrusions that
result in uplift and
folding of the
preexisting rocks
above the
intrusion. They are
also concordant
types of intrusions.
Pluton features
Batholiths are very
large intrusive bodies,
usually so large that
there bottoms are rarely
exposed. Sometimes
they are composed of
several smaller
intrusions.
Stocks are smaller bodies that are likely fed from deeper level
batholiths. Stocks may have been feeders for volcanic eruptions, but
because large amounts of erosion are required to expose a stock or
batholith, the associated volcanic rocks are rarely exposed.
Methods of Igneous Intrusion
Methods of intrusion
Melting - crystallization
Stoping - xenoliths
Injection
Igneous Intrusion