Plate Tectonics

Theory of Plate Tectonics States that Earth’s crust & rigid upper mantle are broken into slabs called plates The plates move in different directions and at different rates The edges of the plates are called Plate Boundaries

Earth Layers

Plate Boundaries There are three types of plate boundaries: –Divergent –Convergent –Transform Let’s look at each type and notice what happens to the plates at these boundaries and what features are formed as a result of what happens.

Divergent Boundaries Plates move apart from each other ← → Results: –Rifts – gap in crust –Ridges - Chain of high land on both sides of the rift Magma freezes and builds up Magma pushing up causes edges of plates to rise

Diverging Boundary

Convergent Boundary Plates move towards each other Results depend on crust type involved –continent vs. continent –continent vs. ocean –ocean vs. ocean

Convergent: continent vs. continent crusts push up mountain building (orogeny) e.g. Indian Plate vs. Eurasian Plate = Himalayan mountains

Continent vs. Continent

Continent vs. Ocean one plate (ocean) sliding under other (continent) in process called subduction. results in trenches, earthquakes, volcanoes on land e.g. Nazca Plate + S. Am. Plate = Peru- Chile trench

Continent vs. Ocean

Ocean vs. Ocean subduction (one of the two subducts) results in trenches, earthquakes, island arcs. e.g. Pacific Plate + Philippine Plate = Marianna Trench, Philippine Islands

Ocean vs. Ocean

Transform Boundary one plate slides past another ↑ ↓ results in earthquakes when built up tension is suddenly released e.g. Pacific Plate + N. Am. Plate = San Andreas Fault

Transform Boundary

Plate Motion Convection –plates are believed to move by convection currents (warmer material increases in volume, becomes less dense and therefore, rises; cooler material condenses, becomes denser and sinks. –diverging boundaries are associated with rising convection currents. –converging boundaries are associated with sinking convection currents

Convection

Plate Motion Ridge Push –process where weight of uplifted ridge pushes plate toward trench. Slab Pull –process where weight of subducting plate helps pull the trailing lithosphere into subduction zone.

Plate Motion

Hot Spots Why are some volcanoes located in the middle of plates? –They are on hot spots –Hawaii is an example Hot Spot –Place in Earth’s crust where magma plume exists and reaches surface –Plume remains stationary –Plate moves over hot spot plume –Chain of volcanoes form

Hot Spots

Hawaii