Plate Tectonics

• Plate Tectonics


  The theory that the Earth's crust is divided into several plates that glide over the mantle
• Seafloor Spreading


  The process where new oceanic crust is formed at mid-ocean ridges as tectonic plates move apart
• Continental Drift


  The theory that the continents have shifted position on the Earth's surface over geological time
• The Earth is a system that interacts with itself. Its subsystems also interact with each other in various ways.
• The lithosphere (or geosphere, depending on the source material) continually changes because of the pent-up stresses deep within it.
• When these stresses are released, the surface begins to shift ever so slightly—or catastrophically, in some cases.
• The Hadean Earth (i.e., the Earth during its primitive stage) was once an undifferentiated, homogeneous mass of solid rock around 4.5 billion years ago.
• Around 500 million years after its formation, the Earth began to sort out its materials based on density.
• Dense materials such as iron sank to the bottom, whereas light materials such as silicates rose above; this is even named the iron catastrophe.
• This event, caused by the planet's temperature exceeding iron's melting point, created distinct layering to Earth: crust, mantle, and core (both inner and outer).
• Types of Earth's crust

  • Continental
  • Oceanic
• Continental crust

  The crust that holds the continents, less dense than oceanic crust because it is made of older material comprising silica and aluminum-based granite
• Lithosphere

  The layer containing the brittle materials that make it rigid, composed of the crust and the upper mantle
• Asthenosphere

  The layer that contains all the liquid and semi-liquid rocks, which can be found in the mantle
• Oceanic crust

  The crust that forms at the bottom of the oceans, denser than continental crust because of its silica and magnesia-based basalt content
• The theory of plate tectonics states that the Earth's crust is divided into several plates that glide over the mantle.
• Major tectonic plates

  • African
  • Antarctic
  • Arabian
  • Australian
  • Caribbean
  • Cocos
  • Eurasian
  • Indian
  • Juan de Fuca
  • Nazca
  • North American
  • Pacific
  • Philippine
  • Scotia
  • South American
• Plate boundary

  The region on the lithosphere where tectonic plates are moving relative to each other
• Divergent boundary

  The plate boundary where seafloor expansion occurs, with plates moving away from each other and creating new plate material
• Divergent boundaries

  • Mid-Atlantic Ridge
  • East Africa Rift System
• Convergent boundary

  The plate boundary where plates collapse and volcanic arcs are made, with plates moving towards each other and one plate subducting under the other
• Transform boundary

  The plate boundary where the plates slide past each other, forming strike-slip faults
• Transform boundaries

  • San Andreas Fault
• Plate movement processes

  • Mantle convection
  • Slab pull
  • Ridge push
• Mantle convection

  The thermodynamic heating of the liquid rocks in the mantle that provides movement to the plates
• Slab pull

  The tensional force exerted by cold, dense oceanic plates as they subduct into the mantle due to their weight
• Ridge push

  Also known as gravitational sliding, it is a proposed driving force that occurs at mid-ocean ridges as the result of the lithosphere sliding down the asthenosphere
• Wilson Cycle

  A theory that correlates plate movement with the Earth's timeline, proposing cycles of rifting and deformations that form and destroy continents and ocean basins
• Stages of the Wilson Cycle

  • Continent Rifting
  • Oceanic Basin and Crust Development
  • Passive Margin Cooling and Sedimentation
  • Volcanic Mountain Belt Formation
  • Subduction Welding
  • Continental Collision
  • Orogenesis
• Evidence/Discoveries supporting Seafloor Spreading

  • Magnetic field
  • Age dating
  • Age and thickness of sediments
• Evidence supporting Continental Drift

  • Fit of continental shorelines
  • Distribution of glacial sediments
  • Paleoclimate
  • Fossil distribution
  • Rock distributions
• Alfred Wegener provided evidence to support the Plate Tectonics theory, but scientists rejected it at the time because he could not give a working mechanism.
• Modern technology from the Second World War led to detailed studies of the seafloor, which supported Wegener's theory.
• Endogenic Processes

  • Volcanism
  • Volcanoes
  • Magma
  • Metamorphism
  • Earthquake
  • Deformation
• Endogenic Processes manifested through

  1. Volcanism

  2. Volcanoes

  3. Magma

  4. Metamorphism

  5. Earthquake

  6. Deformation
• Plate Tectonics

  • Divergent boundary
  • Convergent boundary
  • Transform boundary
• Plate Tectonics

  Explains seafloor spreading
• Plate Tectonics

  Explains continental drift
• Causes of deformation

  • Tension
  • Shearing
  • Compression
• Evidence for plate tectonics

  • Continental fit
  • Glacial sediments
  • Paleoclimate
  • Fossil Distributions
  • Rock Distributions