Tectonic Plates

• Plate Tectonics


  The theory that the Earth's surface is composed of plates that move and interact with each other, causing geological phenomena such as earthquakes, volcanoes, and mountain building
• Plate Tectonics is designed to meet South Carolina Department of Education 2005 Science Academic Standards
• Continental drift theory


  The idea that the continents are situated on slabs of rock, or plates, and they have drifted across the surface of the Earth over time
• Evidence supporting continental drift theory

  • Fossils of the same plant (Glossopteris) found in Australia, India, Antarctica and South America
  • Fossils of same reptile (Mesosaurus) found in Africa and South America
  • Glacial deposits found in current warm climates and warm climate plant fossils found in what is now the Arctic
  • Nearly identical rock formations found on the east coast of U.S. and the west coast of Europe and eastern South America and western Africa
• The idea for Wegener's theory was sparked by his observation of the nearly perfect "fit" of the South American and African continents
• Layers of the Earth

  Core (inner and outer), Mantle, Crust (continental and oceanic)
• Lithosphere


  The rigid outer-most layer of the Earth, consisting of the crust and upper-most mantle
• Asthenosphere


  The partially molten part of the upper mantle, allowing the tectonic plates to move
• Tectonic plates can move centimeters per year, about as fast as your fingernails grow
• Tectonics


  The deformation of the lithosphere, including mountain building
• Plate motion


  1. Driven by heat escaping from the mantle, creating convection currents

  2. Plates move in different directions on a "conveyor belt"
• Types of plate boundaries

  • Convergent
  • Divergent
  • Transform
• Convergent boundary (ocean-continent collision)

  • Oceanic crust is subducted beneath continental crust, creating deep-sea trenches and volcanoes
• Convergent boundary (continent-continent collision)


  • Mountain building occurs, with little volcanic activity
• Convergent boundary (ocean-ocean collision)

  • Older, denser oceanic crust is subducted, creating a chain of volcanic islands (volcanic arc)
• Volcanoes form above subduction zones due to the interaction of fluids and geothermal heat creating new magma
• Divergent boundary (sea-floor spreading)


  • Hot magma rises from the asthenosphere, creating new oceanic crust and a mid-ocean ridge
• Mid-ocean ridges


  • The Mid-Atlantic Ridge, a slow-spreading ridge
  • The East Pacific Rise, a fast-spreading ridge
• Sea-floor exploration


  1. The Deep Sea Drilling Project (DSDP) began in 1968 aboard the research vessel Glomar Challenger

  2. Magnetometer surveys at sea revealed the magnetic striping of the ocean floor
• Before sea-floor exploration, most people thought the ocean floor was flat and smooth
• South Carolina is located on the North American plate

  
• Deep Sea Drilling Project (DSDP)


  Research project that began in 1968 aboard the research vessel Glomar Challenger, which was outfitted with a drill rig capable of drilling into the ocean floor beneath many kilometers of water
• Dredging/grabbing


  Methods used by scientists to collect single rock samples from the ocean floor before the DSDP
• Scientists quickly determined that continental crust is thicker than oceanic crust, that continental crust is less dense than oceanic crust, and that the youngest seafloor is located at mid-ocean ridges and increases in age with distance from the ridge
• Before technology like the DSDP, most people thought the ocean floor was flat and smooth
• Magnetometer surveys


  Surveys that indicated alternating magnetic anomalies existed within marine rock, aligned parallel to the Mid-Atlantic Ridge forming stripe-like patterns on the sea floor, symmetrically distributed on either side of the Mid-Atlantic Ridge
• Magnetic reversals


  The Earth's magnetic field has changed over the past 100 million years, approximately once every 250,000 years, with normal and reversed periods
• The relative age of the sea floor can be determined by changes in magnetic polarities of the earth
• The oldest oceanic crust found is ~ 180 million years old
• Because the age of the earth is ~4,600 million years, we know that oceanic crust is continually being formed at spreading ridges and being destroyed at subduction zones. The ocean floor is constantly changing shape and size through the processes of sea-floor spreading and subduction
• Transform boundary


  When two plates slide past each other moving in different directions or the same direction, characterized by a transform fault and earthquake activity
• Transform fault


  • San Andreas Fault in California
• Transform fault


  • Difference in plate motion along the contact (fault) leads to a buildup of strain energy that sometimes slips releasing a huge amount of energy and causing an earthquake
• Hotspot


  Where the heat from the mantle could affect the thin crust, forming volcanic islands such as Hawaii
• Wilson Cycle


  Concept explaining the origin for the Appalachian Mountains, going through the sequence: 1) The splitting of a supercontinent, 2) the opening of an ocean basin, 3) the closing of the ocean basin, 4) the collision of continents and formation of mountains
• Fault


  Planar rock fractures along which movement has occurred
• Strike-slip fault


  Occurs through shearing when two blocks move in horizontal but opposite directions of each other, can be right-lateral or left-lateral
• Normal fault


  Faults caused by blocks of crust pulling apart under the forces of tension, where the hanging-wall block moves down relative to the foot-wall block
• Reverse fault


  Faults caused by blocks of crust colliding under the forces of compression, where the hanging wall block moves upward (and over) relative to the footwall block
• Folding


  Rocks can undergo folding as well as faulting, particularly if they are subjected to heat and pressure