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A. Endogenous ProcessesEndogenous Processes are large-scale landform
building and transforming processes
– they create relief.
1. Igneous Processes
a. Volcanism: Volcanic eruptions Volcanoes
b. Plutonism: Igneous intrusions
2. Tectonic Processes (Also called Diastrophism)
a. Folding: anticlines, synclines, mountains
b. Faulting: rift valleys, graben, escarpments
c. Lateral Faulting: strike-slip faults
Earthquakes evidence of present-day tectonic activity
Granite quarry
What important
natural resources are
found in igneous
rock?
Steven Earle
Stawamus Chief, Squamish BC
Massive granite
Mafic dyke (~5 m across)
Igneous Rock Igneous rock is formed when molten, or partially molten, rock
solidifies.
Igneous Rocks (two types) Extrusive
Lava and Pyroclastic Debris
Extruded at surface or at very
shallow levels and cooled quickly
Intrusive
Magma crystallized slowly within the crust.
No exposure to the cool atmosphere.
Plutonic – intrusive igneous rock cooled slowly at great depth within crust or mantle.
Basalt is Extrusive
Granite is Intrusive
What is the key textural difference between these two rocks?
Why Study Igneous Rocks?
All rocks on Earth have evolved from the first igneous rocks through Igneous Evolution
Provide information about the composition of the mantle
Absolute age can be obtained through Radiometric Dating
Features are characteristic of a specific tectonic environment
Host important mineral deposits (metal ores)
Numerous other critical economic uses
Millions of people are endangered by volcanoes
Decompression melting
Convection brings hot rock to shallower depths
Rifting lowers pressure
Lower pressure causes a lower melting point
Igneous rock is formed through a process ofcrystallization and magma differentiation
Why does a lower pressure lower the melting point?
Partial Melting Partial Melting
Silica-rich compounds melt before other compounds.
Magma Differentiation
Four types:
Magma mixing
Crystal settling
Wall-rock assimilation
Magma migration
Bowen’s Reaction Series• Describes the order and process of magma crystallization
Bowen’s Reaction Series Animation
How Are Igneous Rocks Named? Texture Texture depends on crystal sizeA. Phaneritic:
Slow cooling (or in the presence of water), larger crystals, Coarse texture, Intrusive or Plutonic
B. Aphanitic:
Rapid cooling , smaller crystals, Finer texture, Extrusive or Volcanic
C. Other textures are Glassy, Pyroclastic, Vesicular, and Porphyritic
Composition Minerals at the TOP of Bowen’s
Dark in color Mafic to Ultramafic
Iron and Magnesium are dark.
How Are Igneous Rocks Named?
CompositionMinerals at the TOP of Bowen’s Dark in color Mafic to Ultramafic Iron and Magnesium are dark.
Minerals at the BOTTOM of Bowen’s Light in color Felsic Sodium plagioclase, potassium plagioclase,
and quartz are light Intermediate composition between these
How is Texture Estimated?
• Texture is estimated using visual grain size• (depends on
crystallization history)
What has to happen for a porphyritic texture to form in an igneous rock?
How is Composition Estimated? Composition is estimated using visual color
Can be misleading
Classification System for Igneous
Rocks
The classification system for igneous rocks is based on the following:
Intrusive and extrusive igneous rocks with the same chemical composition contain the same minerals
Silica content decreases as iron and magnesium content increases
Potassium and sodium content decreases as silica content decreases
Seven Common Types of Igneous
Rock
1) Graniteintrusive
2) Rhyoliteextrusive
Felsic Composition
Seven Common Types of Igneous
Rock
3) Dioriteintrusive
4) Andesiteextrusive
Intermediate Composition
Seven Common Types of Igneous
Rock
Mafic Composition
5) Gabbrointrusive
6) Basaltextrusive
Seven Common Types of Igneous
RockUltramafic Composition
7) Peridotiteintrusive
Igneous Evolution All rocks on Earth have evolved from the first igneous rocks
All Igneous Rocks Result from Magma Differentiation
Tectonic
Processes
Tectonic Processes Igneous rock evolves as a product of tectonic processes and is a
major component of Earth’s crust
What is the mechanism that leads to partial melting above a subductionzone?
Identify the magma source for each type of volcano. How is the magma source responsible for the rock composition?
Basalt Formation (Spreading
Centers) High heat flow creates Hydrothermal (hot water) Vents
(black smokers)
Oceanic crust consists of layers of igneous rock
Gabbro crystallizes at the base
Sheeted dikes of basalt extend above the gabbro
Pillow basalt, glassy fragments and metallic sulfide deposits (at black smokers) form at the sea floor
Basalt Formation (Hot Spots) Intraplate sites of active Plutonism
and Volcanism
Large Igneous Provinces of Flood Basalts form above mantle hot spots
Plumes of anomalously hot mantle rock underly active hot spots. Mantle plumes, which are solid rock, not magma, rise slowly through the mantle (but faster than the rate of mantle convection) due to their positive buoyancy with respect to the surrounding rock.
Basalt is also present at many subduction-related volcanoes, but typically only in minor amounts.
Modern sea-floor pillow basalt
pillow basalt on Vancouver Island
Steven Earle
Igneous Intrusions• Igneous intrusions occur in a variety of sizes and shapes.
Subduction Zones and Spreading
Centre Subduction zones and spreading centers are areas in which
magma is formed as a result of partial melting, plutonism, and volcanism.
What igneous environment is not represented in this image?
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