The lithosphere is broken into separate sections called plates. These plates “float” on top of the Asthenosphere. The theory of plate tectonics explains the formation, movement, and subduction of Earth’s plates.
The crust and part of the upper mantle = lithosphere 100 km thick Less dense than the material below it so it “floats”
The semi-molten layer below the lithosphere =Asthenosphere The plates of the lithosphere float on the Asthenosphere
Ocean plates – lithospheric plates below the oceans Continental plates – lithospheric plates below the continents
At the locations where two tectonic plates interact, a boundary between these plates exist. There are three types of boundaries: divergent boundaries, convergent boundaries, and transform boundaries.
In sea-floor spreading, the two oceanic plates spread apart. Magma reaches the surface, cooling to form new crust. As a result, the ocean floors move like conveyor belts, carrying the continents along with them.
Evidence includes: eruptions of molten material, magnetic stripes in the rock of the ocean floor, and the ages of the rocks themselves (youngest closest to the mid-ocean ridge).
Boundaries between two plates that are colliding There are 3 types…
Ocean –Continental Convergent More dense oceanic plate colliding with a less dense continental plate Subduction Zone: where the more dense plate (oceanic) slides under the less dense plate (continental)
Mountains and possibly volcanoes Examples: Cascade Mtns in Oregon, Washington and Andes Mtns in South America. Trenches (underwater canyons) on ocean floor Examples: Marianas Trench in Pacific Ocean