Guilford County SciVis V205.03 Plate Tectonics Guilford County SciVis V205.03

Plate Tectonics

What is Plate Tectonics The Earth is broken into large Plates. The size and position of Plates change. Plate edges colliding - geologic activity Cause of Earthquakes & Volcanoes Creates Mountains Deep ocean vents – site of creation of life

Earth has 3 Layers Core Mantle Crust

Outer Layers of the Earth The Lithosphere (Greek, Lithos for Stone) is the rigid, outermost layer of outer crust and uppermost mantle. This makes up the “Plate” of Plate Tectonics.

Asthenosphere The Asthenosphere is the solid part of the mantle that “Flows” in a process called plastic behavior. Plastic behavior is much like toothpaste moving in a tube.

Continental Drift Continental Drift theory was proposed by Alfred Wegener in 1912. He used continental fit, distribution of fossils, ancient climates, and the wandering of Earth's polar regions to support his Theory. He stated the present continents were part of a super continent – Pangaea.

Pangaea

Sea-Floor Spreading

Sea-Floor Spreading Harry Hess proposed that new ocean floor is formed at the rift of mid-ocean ridges. The ocean floor, and the rock beneath it, are produced by magma that rises from deeper levels. Hess suggested that the ocean floor moved laterally away from the ridge and plunged into an oceanic trench along the continental margin.

Subduction As new ocean floor is created by sea-floor spreading at the mid-oceanic ridges it is consumed at the subduction zones where the lithosphere sinks under the asthenosphere.

Convergent Boundaries Oceanic-Continental Convergence Continent-Continent Convergence Oceanic-Oceanic Convergence

Oceanic-Continental Convergence When the leading edge of an oceanic crust collides with continental crust. Oceanic crust is denser – it is subducted, or forced under the less dense continental crust. A deep oceanic trench forms along a subduction zone.

Continent-Continent Convergence When two leading edges of continental crust collide. Neither crust is conducted – they have the same density. Colliding edges are crumpled and uplifted, producing mountains.

Oceanic-Oceanic Convergence A collision between oceanic crust and another oceanic crust. A deep ocean trench forms when one of the oceanic crust is subducted. Part of the subducted crust melts to form magma. Molten magma rise to form volcanic islands.

Convergent Boundaries Places where plates crash or crunch into each other. All the folding and bending makes rock in both plates break and slip, causing earthquakes. Rock deep in the Earth melts, builds up pressure causing volcanoes.

Continental Crush An ocean floor will always slide under the land mass. This is because the land mass is more buoyant, or lighter, than the ocean floor. When two land masses meet neither will slide under the other. Instead, the two crush together at what is known as a collisional boundary. They crumple and fold. Some pieces of land are thrust over or under other pieces. The result is a mountain range.

Divergent Boundaries Places where plates come apart are called divergent boundaries. When Earth's brittle surface layer is pulled apart, it breaks along parallel faults that tilt slightly outward from each other. As the plates separate along the boundary, the block between the faults cracks and drops down into the soft, plastic interior. The sinking of the block forms a central valley called a rift. Magma (liquid rock) seeps upward to fill the cracks. In this way, new crust is formed along the boundary.

Divergent Boundaries

Transform Boundaries Places where plates slide past each other are called transform boundaries. The most famous transform boundary in the world is the San Andreas fault. Los Angeles will not crack off and fall into the ocean as popularly thought, but it will simply creep towards San Francisco at about 6 centimeters per year. In 16 million years, the plates will have moved so much that Los Angeles will be north of San Francisco!

Transform Boundaries

Summary Illustration

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