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=NtqumXEHK
Us
Resources
 http://www.earthtoleigh.com
 www.google.com
 Prentice Hall Earth Science