Transcript The Theory of Tectonic Plates

BELLRINGER
List and explain 3 pieces of
evidence that Wegener
used to support the idea of
Pangaea.
The Theory of Tectonic
Plates
Chapter 7 Section 3
The Theory of Plate Tectonics
The Earth’s lithosphere (crust and upper
mantle) is divided into tectonic plates.
 These plates move on top of the
asthenosphere (lower mantle).
 We know that these plates move in
different ways.

Tectonic Plates
Tectonic Plate Boundaries
 A boundary is a place where tectonic
plates touch.
3 types of tectonic plate boundaries:
 Convergent
 Divergent
 Transform
The numbers on the map represent the rate at which plates are moving in
centimeters.
Plate Movement
Convergent Boundary
• When two plates collide, or move toward
each other, the boundary is called
convergent
• There are 3 types of convergent
boundaries, depending on what type of
crust comes together.
• Continental-continental
• Continental-oceanic
• Oceanic-oceanic
Convergent Boundary
Continental-Continental


The two continental plates come together
Buckle, thicken, and push continental crust upward
Convergent Boundary
Continental-Oceanic

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Dense oceanic crust sinks below the continental crust and
sinks into the asthenosphere.
This is a subduction zone.
“Sub” means below (submarine, subway)
Old ocean crust is pushed below the asthenosphere and
gets re-melted and recycled.
Convergent Boundary
Oceanic-Oceanic
► One
oceanic plate sinks below the other.
► Another subduction zone
Divergent Boundary
 Two tectonic plates move away from each other.
 On the sea floor at the mid ocean ridge this is called
sea floor spreading.
 As the plates move apart, magma rises to fill the gaps.
 The magma is cooled and forms new ocean floor.
The volcanic country of Iceland,
which straddles the Mid-Atlantic
Ridge, offers scientists a natural
laboratory for studying on land the
processes also occurring along the
submerged parts of a spreading
ridge. Iceland is splitting along the
spreading center between the North
American and Eurasian Plates, as
North America moves westward
relative to Eurasia.
Divergent Boundary
On-land exposure of the
Mid-Atlantic Ridge in Iceland.
Sea Floor Spreading
Transform Boundary
Two tectonic plates
move past one
another.
Their edges are jagged
and irregular.
As they grind together
and jerk, they slide
past each other
creating earthquakes.
3 Possible Causes of
Plate Movement
1. Convection: hot rock deep in the Earth
rises, cooler rock sinks. This
movement of magma causes plates to
move
2. Ridge push
3. Slab pull
Tracking Tectonic Plate Movement
• Plates move very slowly, centimeters to
inches a year.
• GPS, Global Positioning System,
measures the rate of movement.
• Radio signals beam continuously from
satellites to the Earth.
• By recording the time it takes for the
Ground station to move a given distance,
scientists can measure the speed at
which plates move.