Plate Tectonics The crust in motion
Evidence for Seafloor Spreading Oceanic crust is younger than continental crust Oceanic crust is 250 million years old while continental crust is almost 3 billion years old. Rocks are younger at the mid-ocean ridge and get increasingly older away from the ridge on both sides Age of the Seafloor
Evidence for Seafloor Spreading (continued) Magnetic Clues Magnetic minerals in basaltic rocks align with the Earth’s magnetic field. The magnetic field has reversed several times.
Theory of Plate Tectonics Continental and Oceanic crust is broken up into sections called plates or tectonic plates that move over the Earth’s surface.
Layers Related to Plate Tectonics Lithosphere Asthenosphere Consists of the crust and rigid upper mantle Broken into large pieces called plates. ”Plastic”-like part of the upper mantle. Convection occurs here.
Tectonic Plate Boundaries 3 Main Types of Boundaries Divergent – plates move away from each other Convergent – plates move toward each other Transform – plates slide past each other horizontally
Divergent Boundaries Plates move away from each other Examples of divergent boundaries are the Mid-Atlantic Ridge and the East-Pacific Rise This is where Rifting occurs.
A plume of hot magma rises from deep within the mantle pushing up the crust and causing pressure forcing the continent to break and separate. Lava flows and earthquakes would be seen.
As the rift valley expands two continental plates have been constructed from the original one. The molten rock continues to push the crust apart creating new crust as it does.
As the rift valley expands, water collects forming a sea.
The sea floor continues to spread and the plates get bigger and bigger.
Transform Plate Boundaries Tectonic plates slide past each other with little or no vertical movement or subduction Characteristics include: - Major Earthquakes An example of a transform boundary is the San Andreas fault in California
Transform Boundary Example
Diagram of Transform Boundary
Example of Transform Boundary