volcanism plutonism

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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