9.2 & 9.3 Plate Tectonics

Earth’s Major Plates

The lithosphere is divided up into segments called plates

These plates continually move and change

Move on average of 5 cm a year (about like your fingernail)

Movements are powered by unequal distributions of heat within the Earth

As they move they interact in various ways

Types of Plate Boundaries

Divergent

Convergent

Transform

Divergent Boundaries

Spreading centers

Occurs when 2 plates move apart

Results in upwelling of material form the mantle to create a new ocean floor

Example Part of the Mid-Atlantic Ridge emerges from the

ocean & splits Iceland in half

Divergent Boundaries

Seafloor Spreading: the process where the ocean floor is extended when 2 plates move apart

Oceanic Ridge: underwater mountain range created from a divergent plate boundary Typically 1000 – 4000 km wide

Example: Mid-Atlantic Ridge (runs the length of the Atlantic Ocean separating N & S American Plates from the Eurasian & African Plates

Divergent Boundaries

Rift Valley: deep faulted structure found along the axes of divergent plate boundaries. These can develop on land or on the ocean

floor Narrow Runs the whole length of a mid-ocean ridge

Convergent Boundaries

Boundary where 2 plates move together

Results in oceanic lithosphere going beneath an overriding plate, and descending into the mantle The India Plate pushing upward into Eurasian Plate

and creating the Himalayan Mountains

Plates carrying continental crust are currently moving toward each other and could one day collide and merge

Boundary that once separated the 2 plates would disappear when the 2 plates join

Convergent Boundaries

Subduction zone: a destructive plate where oceanic crust is pushed down into the mantle under the second plate

Ocean-Ocean Boundary: when 2 oceanic pieces converge, 1 goes under the other. Volcanoes form under the ocean.

Ocean – Continental Boundary: when the continental plate converges with an oceanic plate, the less dense continental plate floats. May cause volcanic eruptions.

Continental – Continental Boundary: when an oceanic plate is subducted under the continental. A volcanic arc forms

Ocean – Ocean Boundary

Ocean – Continental Boundary

Continental – Continental Boundary

Transform Fault Boundaries

2 plates are sliding past one another without production or destruction of the lithosphere

Example: San Andreas Fault is 800 km long and runs throughout California

Plate Boundaries Video

https://www.youtube.com/watch?v=NtqumXEHKUs

Resources

http://www.earthtoleigh.com

www.google.com

Prentice Hall Earth Science