Plate Tectonics

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Plate Tectonics

• Joy Nowak

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What is plate tectonics?

• A plate is a large, rigid slab of rock.
• The word tectonics comes from the Greek root to
  build.
• The Earths surface is built of plates.
• The theory of plate tectonics states that the
  Earths outermost layer is fragmented into twelve
  or more large and small plates that are moving
  relative to one another as they ride atop a
  hotter, more mobile material.

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Ocean and continental plates.

• Continental plates are thicker but less dense.
• Ocean plates are thinner but more dense.

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Earths top layers

• Top layer is called the lithoshere, which
  contains the crust and the uppermost part of the
  rigid mantle.
• Under the lithosphere is the asthenosphere.
• Asthenosphere consists of of a solid but low
  viscosity which can make it flow like liquid.
• Below the asthenosphere is the deeper mantle
  which is more rigid.

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Continental drift

• The Earths plates are in constant motion.
• The continents that we know today were once one
  super continent known as Pangaea.
• Over time the continent began to split slowly
  creating seven continents.

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What drives the plates?

• Harry Hess theory is that the plate-driving
  force is the slow movement of hot, softened
  mantle that lies below the rigid plates.
• Moving rock beneath the rigid plates is believed
  to be moving in a circular motion.

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• The heated rock rises to the surface, spreads,
  cools, then sinks back to down. This cycle is
  called convection cell or convective flow which
  causes plate movement.
• The plates move very slowly on the surface, only
  about two inches a year on average.

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Plate boundaries

• There are three types of plate boundaries and are
  characterized by the way the plates move relative
  to each other.
• Each boundary causes different reactions.

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Transform boundaries

• Plates next to each other slide past each other.
• The plates grind past each other on transform
  faults causing earthquakes.
• The San Andreas fault in California is a
  transform boundary that has caused many
  earthquakes.

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Convergent boundaries

• Two plates slide towards each other causing
  either a subduction zone or a continental
  collision.
• A subduction zone is when one plate moves
  underneath the other which can cause Earthquakes,
  tsunamis, and volcanic activity.
• Continental collision causes the plates to hit
  each other and raise above the surface causing
  mountain ranges.

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Divergent boundaries

• Occur where to plates slide apart from each
  other.
• The separating plates move apart and new crust is
  created by magma pushing up from the mantle.
• The Mid-Atlantic ridge is a submerged mountain
  range from the Artic Ocean to beyond the southern
  most tip of Africa. This was caused by divergent
  boundaries.

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Sources

• http//en.wikipedia.org/wiki/Plate_tectonics
• This Dynamic Earth The Story of Plate Tectonics
  by W. Jacquelyne Kious and Robert I. Tilling
  (online book through usgs.org)
• http//pubs.usgs.gov/gip/dynamic/understanding.htm
  lanchor6715825

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• http//volcano.und.edu/vwdocs/vwlessons/lessons/Pl
  ates/Plates11.html
• http//www.windows.ucar.edu/tour/link/teacher_res
  ources/teach_snacktectonics.html
• http//www.astronomynotes.com/solarsys/plates-coll
  ide.png