Plate Tectonics

Theory of Plate Tectonics Meaning – “plate structure” Developed – 1960’s Explains the movement of Earth’s plates, causes of volcanoes, earthquakes, ocean trenches, mountain formation, and other geological phenomena.

Plates move about 1-10 cm per year!!! Seismic activity (volcanoes and earthquakes) occur as plate boundaries interact.

Plate Boundaries There are 3 types of plate boundaries: Divergent Convergent Transform

Divergent – movement of 2 plates away from each other

Convergent – colliding of 2 plates

Transform – plates sliding horizontally past each other.

Earth’s Major Plates EurasianCaribbean Australian-IndianSouth American PacificAfrican Juan de FucaAntarctic North American

Earth’s Major Plates

Crust –Oceanic –thin, under ocean crust is thin and not very dense, active –Continental – thick, under land, constantly created and destroyed.

Plate Tectonics Animation Y1dmEhttp:// Y1dmE

Sea- floor Spreading The longest chain of mountains in the world is the Mid-Ocean Ridge. Scientists have mapped the ocean floor and mid- ocean ridge using S.O.N.A.R. The mid-ocean ridge extends into all of Earth’s oceans. The Island of Iceland is part of the ridge that rises above the surface in the Atlantic Ocean. Down the middle of the ridge is an area called the rift valley – It is almost twice as deep as the Grand Canyon

Harry Hess Harry Hess examined maps of the mid-ocean ridge and proposed that the ocean floors move like conveyor belts, carrying the continents along with them. This movement begins at the Mid- Ocean Ridge. At the ridge, the molten material rises from the mantle and erupts (much like a volcano). The oldest rock is farthest from the center of the ridge. Harry Hess first proposed the idea of Sea-Floor Spreading.

Evidence for Sea-Floor Spreading: Molten Material. The submersible ALVIN was sent down to study the rift valley.

Evidence Rock Sampling. The Glomar Challenger was a drilling ship the gathered samples from the ocean floor. The scientists determined the age- of the rocks in the samples and found that the farther-away from the ridge, the older the rocks were. The oldest rocks are about 4 million years old. The newer rocks were always in the center of the ridges

Evidence Magnetic Stripes. How does the pattern of matching stripes show evidence of sea- floor spreading?

How does the ocean floor keep getting wider The ocean floor plunges into deep under water trenches. A deep ocean trench forms where the oceanic crust collides with continental crust. Subduction is the process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

FYI Most ocean trenches are found in the Pacific Ocean. The deepest part of the ocean is the Marianna’s Deep. It is located in the Pacific Ocean The Pacific Ocean is shrinking, but it is still the Largest ocean