Download Seafloor Spreading

Mid-Ocean Ridge
4.2 Seafloor Spreading
Mid-Ocean Ridge (MOR)
• Longest mountain range found on Earth
• Located in the middle of the seafloor
• Mapped by sonar
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Seafloor Movement at the MOR
• New seafloor is constantly being made at
mid-ocean ridges.
• Hot material in the mantle moves toward
Earth’s surface by convection.
• Lava flows
through the
cracks along the
mid-ocean ridge,
cools, and forms
new seafloor.
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4.2 Seafloor Spreading
Seafloor Spreading
• Seafloor spreading is the process by which
seafloor is continually made at the MOR.
• Explains continental drift hypothesis
• Seafloor age increases as distance from the
mid-ocean ridge increases. (p. 174)
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Evidence for
SEA-FLOOR SPREADING
4.2 Seafloor Spreading
Evidence for Spreading
• Earth’s magnetic poles have
reversed several times.
• As oceanic crust forms from lava
and cools, tiny crystals record
the magnetic field
orientation.
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4.2 Seafloor Spreading
Seafloor Drilling
• Confirmed that the oldest rocks
are located furthest from the
mid-ocean ridge
• Supported seafloor spreading
hypothesis (p.174)
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Subduction
What happens to the ocean crust?
• The oceanic crust bends and breaks as it
sinks down into the mantle, causing
earthquakes.
• We call this process SUBDUCTION.
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Subduction
• Slabs are
cooler, denser
lithospheric
plates that sink
down into the
mantle.
• An Ocean Trench is formed where the
oceanic crust subducts.
• Subduction will occur when 2 oceanic
plates collide, or when an oceanic and a
continental plate collide. (p. 218)
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