Download - Tectonic plates 2
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The Structure of the Earth and Plate Tectonics
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Structure of the Earth
• The Earth is made up of 4 main layers:– Inner Core– Outer Core– Mantle– Crust
Inner core
Outer core
Mantle
Crust
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The Crust• This is where we live!
• The Earth’s crust is made of:
Continental Crust
- thick (10-70km)- buoyant (less dense than oceanic crust) - mostly old
Oceanic Crust
- thin (~7 km)- dense (sinks under continental crust)- young
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How do we know what the Earth is made of?
• Geophysical surveys: seismic, gravity, magnetics, electrical, geodesy– Acquisition: land, air, sea and satellite– Geological surveys: fieldwork, boreholes, mines
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What is Plate Tectonics?
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• If you look at a map of the world, you may notice that some of the continents could fit together like pieces of a puzzle.
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Alfred WegenerAlfred Wegener
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Alfred WegenerAlfred Wegener – proposed that in the distant past, the Earth’s continents were all joined as a single landmass.
-South America and Africa would fit remarkably well, shoreline to shoreline.
-If the Americas were moved next to Africa and Europe, there would be a match of ancient continental rocks and tectonic (fold and fault) structures.
-PangaeaPangaea – when Wegener placed all the continents together like a puzzle, it formed a large landmass which he called Pangaea.
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Pangaea Puzzle!
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Plate Tectonics
• The Earth’s crust is divided into 12 major plates which are moved in various directions.
• This plate motion causes them to collide, pull apart, or scrape against each other.
• Each type of interaction causes a characteristic set of Earth structures or “tectonic” features.
• The word, tectonic, refers to the deformation of the crust as a consequence of plate interaction.
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World Plates
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What are tectonic plates made of?
• Plates are made of rigid lithosphere.
The lithosphere is made up of the crust and the upper part of the mantle.
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What lies beneath the tectonic plates?
• Below the lithosphere (which makes up the tectonic plates) is the asthenosphere.
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Plate Movement
• “Plates” of lithosphere are moved around by the underlying hot mantle convection cells
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What happens at tectonic plate boundaries?
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• Divergent
• Convergent
• Transform
Three types of plate boundary
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• Spreading ridges– As plates move apart new material is erupted to fill
the gap
Divergent Boundaries
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Age of Oceanic Crust
Courtesy of www.ngdc.noaa.gov
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• Iceland has a divergent plate boundary running through its middle
Iceland: An example of continental rifting
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• There are three styles of convergent plate boundaries– Continent-continent collision– Continent-oceanic crust collision– Ocean-ocean collision
Convergent Boundaries
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• Forms mountains, e.g. European Alps, Himalayas
Continent-Continent Collision
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Himalayas
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• Called SUBDUCTION
Continent-Oceanic Crust Collision
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• Oceanic lithosphere subducts underneath the continental lithosphere
• Oceanic lithosphere heats and dehydrates as it subsides
• The melt rises forming volcanism
• E.g. The Andes
Subduction
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• When two oceanic plates collide, one runs over the other which causes it to sink into the mantle forming a subduction zone.
• The subducting plate is bent downward to form a very deep depression in the ocean floor called a trench.
• The worlds deepest parts of the ocean are found along trenches. – E.g. The Mariana Trench is 11 km deep!
Ocean-Ocean Plate Collision
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• Where plates slide past each other
Transform Boundaries
Above: View of the San Andreas transform fault
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Practical Exercise 2
Where will the UK be in:1,000 years?
1,000,000 years?
1,000,000,000 years?
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…what’s the connection?
Volcanoes and Plate Tectonics…
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Volcanism is mostly focused at plate margins
Pacific Ring of Fire
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- Subduction - Rifting - Hotspots
Volcanoes are formed by:
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Pacific Ring of Fire
Hotspot volcanoes
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• Hot mantle plumes breaching the surface in the middle of a tectonic plate
What are Hotspot Volcanoes?
Photo: Tom Pfeiffer / www.volcanodiscovery.com
The Hawaiian island chain are examples of hotspot volcanoes.
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The tectonic plate moves over a fixed hotspot forming a chain of volcanoes.
The volcanoes get younger from one end to the other.
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…what’s the connection?
Earthquakes and Plate Tectonics…
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• As with volcanoes, earthquakes are not randomly distributed over the globe
• At the boundaries between plates, friction causes them to stick together. When built up energy causes them to break, earthquakes occur.
Figure showing the distribution of earthquakes around the globe
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Where do earthquakes form?
Figure showing the tectonic setting of earthquakes
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Plate Tectonics Summary
• The Earth is made up of 3 main layers (core, mantle, crust)
• On the surface of the Earth are tectonic plates that slowly move around the globe
• Plates are made of crust and upper mantle (lithosphere)
• There are 2 types of plate• There are 3 types of plate boundaries• Volcanoes and Earthquakes are closely linked to
the margins of the tectonic plates