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Sea Floor spreading and Subduction. How The P lates M ove. Sea floor spreading. The process by which new ocean lithosphere is created as the older rock material is pulled away. Sea floor Spreading …. Takes place where plate edges meet. M ost often underneath the ocean
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Sea Floor spreading and Subduction How The Plates Move
Sea floor spreading • The process by which new ocean lithosphere is created as the older rock material is pulled away.
Sea floor Spreading … • Takes place where plate edges meet. Most often underneath the ocean • Molten rock (magma) spurts up between the plates. • As the magma is cooled by the ocean water it forms new crust. • This new crust creates ocean ridges
Sea Floor spreading • This process keeps repeating so new crust is constantly being formed • The crust increases in age the further it is from the ocean ridge
What is our evidence that the crust at the ridges is the youngest?
Magma contains magnetic minerals • These magnetic minerals align with the magnetic field of the Earth – they move toward the north pole
Magnetic Reversals • The (magnetic)North and South pole have switched places many times in Earth’s history • Switching places is called “magnetic reversal” • So the magnetic minerals have created bands or stripes in the crust
How the sea floor spreads -Ridge Push • Two plates come apart in the ocean • Magma rises to fill in the gap and when it cools it forms a ridge (extra rock crust) • The extra weight of the ridge (extra rock crust) puts pressure on the asthenosphere causing magma to rise again
Sea floor spreading features • Rift – is the area of separating plates • Rift valley – is the valley that forms between the ridges • Ridge - is the mountain that is formed by the build up of cooled magma
http://app.discoveryeducation.com/search?Ntt=sea+floor+spreadinghttp://app.discoveryeducation.com/search?Ntt=sea+floor+spreading
No! The Earth recycles itself in a process called Slab pull – or SUBDUCTION • As the ridges push out new crust the old crust is pulled back down into the mantle. • A slab pull is when the plates are pulled down into the mantle.
At the Mid Atlantic Ridge the plates are pulling apart, at the Nazca and S. American plate the plates are colliding and subducting
Trenches and sometimes volcanoes • Trench – is a ditch like feature formed by subduction • Composite Volcanoes
Picture Citations • http://www.pmel.noaa.gov/vents/nemo/education/images/seafloor_spreading.jpg • http://www.womenoceanographers.org/Content/Profiles/MelanieSummit/images/LearnMore1.jpg • http://www.pmel.noaa.gov/vents/nemo/education/images/seafloor_spreading.jpg • http://www.answersingenesis.org/assets/images/articles/am/v2/n2/figure-2-c.jpg