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

Cross-section 1 Cross-section 3 Cross-section 2 AB A A B B

MOR Oceanic trench Continental volcanic arc Constructive plate boundary Destructive plate boundary Cross-section 1 AB

Oceanic trench Island arc volcano Destructive plate boundary Cross-section 2 A B

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 Zone Inclined zone where earthquakes occur Constructive Plate Margin Destructive Plate Margin Shallow focus earthquakes 0 – 70km

Constructive Plate Margins Transform fault Mid-Oceanic ridge Rift valley Basaltic, shield volcano Strong, solid, brittle layer Weak, mobile, semi-molten layer (<1% molten) Low angled (< 10°) Non-explosive (effusive) Volcanic tremor (rising magma) Tectonic tremor (transform fault) Tectonic tremor (normal faults)

Evidence for Plate Tectonics Mid-Atlantic Ridge

Constructive Plate Margins Peridotite Basaltic Partial melting Peridotite (Ultra-basic) Basic magma Intermediate magma Acidic magma - Basaltic - Andesitic - Rhyolitic Basalt Dolerite Gabbro

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 Arc Subduction 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 Theory 1. 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 MarginConstructive Plate Margin MOR Basaltic Magma Decompression Melting Oceanic Crust Lithosphere Asthenosphere Subducting Slab Hydration Melting Asthenosphere Lithosphere Andesitic Magma Continental Crust Continental Volcano Oceanic Trench Benioff Zone

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

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 LatitudeMagnetic Angle 0°0°0°0° 30°50° 60°70° 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