Download Oceanic Crust

Oceanic Crust
Objectives:
1. To be able to define what oceanic crust
is;
2. To be able to explain how oceanic crust
forms;
3. To be able to describe the composition
of oceanic crust; and
4. To be able to draw a diagram of the
structure of oceanic crust.
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).
Formation
1. Oceanic crust is created at midocean/oceanic ridges and destroyed by being
pulled back into the mantle in subduction
zones by the processes of plate tectonics.
2. Most of the present day oceanic crust is less
than 200 million years old because it is
continuously being recycled.
3. Seafloor spreading forms oceanic crust.
Composition
1. Oceanic crust is
composed of mafic
basaltic rocks.
2. See Ophiolite link for
more on
composition.
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)
Structure (cont.)
Structure (cont.)
Watch the Seafloor Move
Subduction Zones
Conclusion
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Formed by seafloor spreading
Composed of basaltic rock (higher in iron)
Ophiolite structure
Destroyed at Subduction Zones
Cascadia Subduction Zone in California