Transcript Theory of Plate Tectonics

Theory of Plate Tectonics
• The lithosphere is broken into separate sections
called plates
• The theory of plate tectonics states that the
pieces of Earth’s lithosphere are in constant
slow motion driven by convection currents in the
mantle.
• No plate can move without affecting the other
plates. As plates move, they change the Earth’s
surface (creating volcanoes,, mountain ranges,
etc.)
Plate boundaries
• Plate boundaries are where plates meet
• Faults may form along these boundaries.
Faults are breaks in the Earth’s crust
where rocks have slipped past each other.
• There are 3 kinds of plate boundaries
– Transform
– Divergent
– Convergent
Transform Boundaries
• In a transform
boundary, the crust is
neither created or
destroyed
• At transform
boundaries, two
plates slip past each
other in opposite
directions.
Divergent Boundaries
• The place where
two plates move
apart
– This can cause a
mid-ocean ridge
(ocean) or a rift
valley (land)
Divergent Boundaries
• On land, when continents split apart a rift
valley is formed.
• The valley floor sinks lower and lower until
it s below sea level.
• Red Sea was formed from a rift valley.
Convergent Boundaries
• A convergent boundary is the place where 2
plates come together resulting in a collision that
can bring together.
– Oceanic crust and oceanic crust
– Oceanic and Continental
– Continental and continental
• Where these two plates collide the density of the
plates determines which will come out on top
• (Oceanic crust is more dense than Continental
Crust)
When two plates collide
• Oceanic → ←Continental
– Because ocean is more dense than continent. The
ocean plates sinks and plunges beneath continent.
This is subduction (the sinking below)
• Oceanic → ← Oceanic
– 2 Plates meet at a trench the more dense plate drives
the other under. This is subduction (the sinking below)
• Continental → ← Continental
– Head on collision creates mountain ranges
Oceanic → ←Oceanic
• 2 oceanic plates collide. The older plate
sinks because it is colder and denser than
the younger plate.
• Oceanic-Oceanic subduction can also
create Deep-Ocean trenches and Island
Arcs
Deep-Ocean trenches
• Deep ocean trenches are deep canyons
that form when a plate sinks. Most are
found in the Pacific Ocean. Best example
is Mariana’s Trench.
Island Arcs
• These are a chain
of volcanic islands
that form the top
plate parallel to a
deep-ocean trench.
Examples are the
Philippine Islands,
Aleutian Islands of
Alaska and the
islands of Japan
Trench (darker blue)
Aleutian Island Arc
Oceanic → ←Continental
• Deep Ocean Trenches also occur when land
and ocean plates collide and one sinks. The
pacific Plate and Juan de Fuca Plate are sinking
under the North American Plate and the This
often causes underwater earthquakes
View across a bridge near Parkfield,
from the North American Plate to the
Pacific Plate. The bent rail is due to the
motion of the San Andreas fault under
the bridge since it was built.
Oceanic → ←Continental
• Coastal Mountains in Oregon and
Washington are examples of when an
oceanic crust sinks under a continental
crust. The continental crust will buckle to
form a mountain range. These mountain
ranges usually parallel a deep-ocean
trench.