Oceanic Crust

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Oceanic Crust

• Objectives
• To be able to define what oceanic crust is
• To be able to explain how oceanic crust forms
• To be able to describe the composition of oceanic
  crust and
• To be able to draw a diagram of the structure of
  oceanic crust.

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Definition

• The oceanic crust is the part of Earth's
  lithosphere which underlies the ocean basins. It
  is thinner (generally less than 10 km thick) but
  more dense than continental crust, about 3.3 g/cc
  (grams per cubic centimeter).

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Formation

• Oceanic crust is created at mid-ocean/oceanic
  ridges and destroyed by being pulled back into
  the mantle in subduction zones by the processes
  of plate tectonics.
• Most of the present day oceanic crust is less
  than 200 million years old because it is
  continuously being recycled.
• Seafloor spreading forms oceanic crust.

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Composition

• Oceanic crust is composed of mafic basaltic
  rocks.
• See Ophiolite link for more on composition.

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Structure

• It is also more dense than continental crust and
  considerably thinner averaging 5-10 km versus the
  average continental crust thickness of around 20
  to 80 km.
• Oceanic crust is coarsest at its bottom and is
  finer grained at its top.
• About 60 of the Earth's surface is underlain by
  oceanic crust.
• Ophiolite Sequence structure (see diagrams)

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Structure (cont.)
7
Structure (cont.)
Watch the Seafloor Move
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Subduction Zones
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(No Transcript)
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Conclusion

• Formed by seafloor spreading
• Composed of basaltic rock (higher in iron)
• Ophiolite structure
• Destroyed at Subduction Zones
• Cascadia Subduction Zone in California