Plate Tectonics

Learning Outcomes:

By the end of the lesson you should be able to...

1.Name and label the major relief features of the Earth on a world map and cross-sections through the Earth’s surface

2.Name the different types of plate boundary that exist on a map of the major relief features of the Earth and indicate the direction of plate movement.

Major Relief Features of the Earth

Ocean Basins•Mid-oceanic ridges•Ocean trenches•Rift valleys•Volcanic island chains•Mountain belts (volcanic island arcs)

Continents•Mountain belts (non-volcanic)•Mountain belts (continental volcanic arcs)

Plate Boundaries•Constructive

•Destructive

•Conservative

Mid-oceanic Ridge

Rift Valley

Ocean Trench

Abyssal Plain

Major Relief Features of the Earth

Major Relief Features of the Earth

Cross-section 1

Cross-section 3

Cross-section 2

A B A

A

B

B

MOROceanic trench

Continental volcanic

arc

Constructive plate boundary

Destructive plate boundary

Cross-section 1Cross-section 1

A B

Oceanic trench

Island arc volcano

Destructive plate boundary

Cross-section 2

Cross-section 2

A

B

Cross-section 3

Cross-section 3

A

B

Destructive plate boundary

Mountain belt (non-volcanic)

Learning Outcomes:

By the end of the lesson you should be able to...

1.Define the characteristics of the upper layers of Earth involved in plate tectonics.

2.Explain the importance of the asthenosphere in plate tectonic theory.

3.Outline the theory of plate tectonics.

Plate Tectonic Theory

Constructive plate margins

Destructive plate margins

Conservative plate margins

Plate Tectonic Theory

Learning Outcomes:

By the end of the lesson you should be able to...

1.Describe the relationship between seismicity, volcanicity and plate boundaries.

2.Explain the distribution of earthquakes and volcanoes.

Plate Tectonic Theory

Shallow focus earthquakes 0 – 70km

Intermediate focus earthquakes 70 – 300km

Deep focus earthquakes 300 – 700km

Benioff ZoneInclined zone where earthquakes occur

Constructive Plate Margin

Destructive Plate Margin

Shallow focus earthquakes 0 – 70km

Constructive Plate Margins

Transform fault

Mid-Oceanic ridge

Rift valleyBasaltic, shield volcano

Strong, solid, brittle layer

Weak, mobile, semi-molten layer (<1% molten)

•Low angled (< 10°)

•Non-explosive (effusive)

Volcanic tremor (rising magma)

1

2

3

Tectonic tremor (transform fault)Tectonic tremor (normal faults)

Evidence for Plate Tectonics

Mid-Atlantic Ridge

Constructive Plate Margins

Peridotite BasalticPartial melting

Peridotite (Ultra-basic)

Basic magma

Intermediate magma

Acidic magma

- Basaltic

- Andesitic

- Rhyolitic

Basalt

DoleriteGabbro

Constructive Plate Margins

Destructive Plate Margins

Mt Pinatubo, Philippines Andesitic, cone-shaped volcano, explosive

Benioff Zone

Oceanic Trench

Partial melting of basaltic oceanic crust

Volcanic Island ArcSubduction

of denser oceanic crust

Deep focus earthquakes

Shallow focus earthquakes

Destructive Plate Margins

Conservative Plate Margins

6 cm/year 2 cm/year

San Andreas Fault

Hot Spots – oceanic lithosphere

Hot Spots – continental lithosphere

Plate Tectonic Theory1. Evidence for Earth’s internal heat energy:

• volcanoes

• hot springs

• deep mines

2. Causes for Earth’s internal heat energy:

• radioactive decay in the mantle & crust

• iron crystallisation in core

• residual heat from Earth formation

3. How is heat transferred from Earth interior?:

• conduction

• convection

4. What is the theory of plate tectonics?:

• The upper part of the mantle and overlying crust form the rigid lithosphere.• The lithosphere is split up into 7 large and many smaller sections known as lithospheric plates.

• These plates are underlain by a semi-mobile zone in the upper mantle known as the asthenosphere.

• Convection currents in the mantle cause the plates to move over the asthenosphere, either moving apart, together or against each other.

Earth’s Major Features and Plate Tectonics

Destructive Plate Margin

Constructive Plate Margin

MOR

Basaltic Magma

Decompression Melting

Oceanic Crust

Lithosphere

Asthenosphere

Subd

ucting

Sla

b

Hyd

ration

Mel

ting

Asthenosphere

Lithosphere

Andesitic Magma

Continental Crust

Continental Volcano Oceanic Trench

Ben

ioff Z

one

Learning Outcomes:

By the end of the lesson you should be able to...

1.Outline how palaeomagnetism can be used to plot plate movements over time.2.Plan a response to an exam essay question.

Learning Outcomes:

By the end of the lesson you should be able to...

1.Outline how palaeomagnetism can be used to plot plate movements over time.2.Plan a response to an exam essay question.

Outline how palaeomagnetism can be used to plot plate movements over time. (25 marks)

• Iron minerals in basalt e.g. magnetite

• Rotate & align with magnetic field

• Remain in this position after magma cools – remnant magnetism

• Magnetic reversals

• New magnetite minerals magma iron aligns in different direction

Palaeomagnetism

• Liquid basalt

• Basalt cools below Curie point (< 570° C for magnetite)

• Earth’s magnetic field

• Magnetic anomalies at constructive plate margins

• Apparent polar wandering curves• Magnetic inclination gives latitude of erupted basalt

Evidence for Plate Tectonics

Magnetic Anomalies at MOR

Magnetic Anomalies at MOR

Calculate the rate the oceanic crust is moving away from the MOR. Your answer should be in mm/year.

60km

Earth’s magnetic field

Orientation of magnetic iron minerals in lavas formed at different latitudes

Earth’s Magnetic Field

Latitude Magnetic Angle

0° 0°

30° 50°

60° 70°

90° 90°

Magnetic Anomalies

Sediment

Basaltic pillow lavas & dolerite dykes

Gabbro

MOR very high heat

flow

Volcanic arc high heat flow Ocean trench

very low heat flow