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
Ocean Trench
Mid-oceanic Ridge
Rift Valley
Abyssal Plain
Major Relief Features of the Earth
Major Relief Features of the Earth
Cross-section 3
Cross-section 2
A
Cross-section 1
B
Cross-section 1
Cross-section 1
A
Oceanic
trench
Continental
volcanic arc
Destructive
plate boundary
MOR
Constructive
plate boundary
B
Cross-section 2
Cross-section 2
Island arc
volcano
Oceanic
trench
Destructive
plate boundary
Cross-section 3
Cross-section 3
Mountain belt
(non-volcanic)
Destructive
plate boundary
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
Plate Tectonic Theory
Constructive plate
margins
Destructive plate
margins
Conservative plate
margins
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
Destructive
Plate Margin
Shallow focus
earthquakes 0 – 70km
Benioff Zone
Inclined zone where
earthquakes occur
Intermediate focus
earthquakes 70 – 300km
Deep focus earthquakes 300 – 700km
Constructive
Plate Margin
Shallow focus
earthquakes 0 – 70km
Constructive Plate Margins
•Low angled (< 10°)
•Non-explosive (effusive)
Basaltic, shield volcano
Mid-Oceanic
ridge
Rift valley
Transform
fault
Tectonic tremor (transform fault) 2
Tectonic tremor (normal faults)
Strong, solid, brittle layer
Weak, mobile, semi-molten
layer (<1% molten)
3
1 Volcanic tremor (rising magma)
Evidence for Plate Tectonics
Mid-Atlantic
Ridge
Constructive Plate Margins
Acidic magma - Rhyolitic
Intermediate
magma
- Andesitic
Basic magma
- Basaltic
Peridotite
(Ultra-basic)
Basalt
Dolerite
Gabbro
Peridotite
Partial melting
Basaltic
Constructive Plate Margins
Destructive Plate Margins
Subduction of
denser
oceanic crust
Oceanic
Trench
Volcanic
Island Arc
Benioff Zone
Shallow focus
earthquakes
Partial
melting of
basaltic
oceanic crust
Mt Pinatubo, Philippines
Deep focus
earthquakes
Andesitic, cone-shaped volcano, explosive
Destructive Plate Margins
Conservative Plate Margins
San Andreas Fault
6 cm/year
2 cm/year
Hot Spots – oceanic lithosphere
Hot Spots – continental lithosphere
Plate Tectonic Theory
1. Evidence for Earth’s internal heat energy:
• volcanoes
3. How is heat transferred from Earth
interior?:
• hot springs
• conduction
• deep mines
• convection
2. Causes for Earth’s internal heat energy:
• radioactive decay in the mantle & crust
• iron crystallisation in core
• residual heat from Earth formation
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 semimobile 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
Continental Volcano
Constructive Plate Margin
MOR
Oceanic Trench
Oceanic Crust
Continental Crust
Andesitic Magma
Lithosphere
Lithosphere
Asthenosphere
Asthenosphere
Basaltic Magma
Decompression
Melting
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)
Palaeomagnetism
• Earth’s magnetic field
• Liquid basalt
• Iron minerals in basalt e.g. magnetite
• Basalt cools below Curie point (< 570° C for magnetite)
• Rotate & align with magnetic field
• Remain in this position after magma cools –
remnant magnetism
• Apparent polar wandering curves
• Magnetic inclination gives latitude of
erupted basalt
• Magnetic reversals
• New magnetite minerals magma
iron aligns in different direction
• Magnetic anomalies at
constructive plate margins
Evidence for Plate Tectonics
Magnetic Anomalies at MOR
Magnetic Anomalies at MOR
60km
Calculate the rate the oceanic crust is moving away
from the MOR. Your answer should be in mm/year.
Earth’s Magnetic Field
Earth’s magnetic field
Orientation of magnetic iron
minerals in lavas formed at
different latitudes
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