Transcript Plate_Tectonics_Power_Point

Plate Tectonics
Science I
Amy Urling
Plate Tectonics Theory
• The Earth’s rigid lithosphere is broken into plates
that move on the pliable asthenosphere.
• In 1912, Alfred Wegener, proposed this theory of
continental drift (that the continents have moved
over time).
• By the 1970s this theory was well-accepted and
explains why volcanoes and earthquakes occur
where they do.
How Do The Plates Move?
Mantle convection: Magma
which is hotter and less
dense than its surroundings
rises upward at mid-ocean
ridges. The convection
current then moves away
from the ridge and draws the
lithospheric plate with it.
The cooler, denser rock then
sinks down at a subduction
boundary.
Types of Plate Boundaries
• Divergent
Boundaries
• Convergent
Boundaries
– Subduction
Zones
– Collision
Boundaries
• Transform
Boundaries
Divergent Boundaries
At these zones, two plates are moving away from
each other. In the gap formed between the two
plates, magma wells up from the mantle to form a
chain of volcanoes creating long ridges. All of
these zones are found under the ocean (except
Iceland) and are called mid-ocean ridges.
Convergent Boundaries –
Subduction Zones
In subduction zones, heavier oceanic plates
slide under lighter continental plates and melt
into magma. Many volcanoes and earthquakes
occur at these zones. An example is along the
western coast of North America.
Convergent Boundaries –
Collision Zones
In collision zones, two
continental plates collide
and form folded mountain
ranges. An example is
where the Australian
Plate collides with the
Eurasian Plate to form the
Himalayan Mountains.
Mount Everest
Transform Boundaries
These boundaries
occur where two
plates are sliding past
each other. This forms
transform faults such
as the San Andreas
Fault in CA where the
Pacific Plate is
moving past the North
American Plate.
Summary of Plate Boundaries
Boundary Type
Surface Feature
Earthquakes
Divergent
Mid Ocean Ridges
Shallow depths only
Convergent
Subduction
Collision
Volcanoes/trenches
High folded mountains
Shallow to deep
All depths
Transform
Earthquake faults
Shallow to medium
Evidence for Plate Tectonics
Shape of Continents
The continents fit together
like puzzle pieces. Around
400 million years ago, one
super-continent Pangaea
existed and slowly the
continents have drifted apart.
For example, the rock types,
ages and fossil evidence on
the west coast of Africa
matches that on the east
coast of South America.
Evidence for Plate Tectonics
Earthquake and Volcano Patterns
Earthquakes and
volcanoes tend to
occur along plate
boundaries. For
example, the “Ring of
Fire” is a continuous
line of volcanoes
around the Pacific
Ocean.
Hot Spot Volcanoes
Some volcanoes are
found in the middle
of tectonic plates.
These volcanoes
form from mantle
hot spots which melt
the plate above. As
the plate moves,
chains of islands can
form.
The Hawaiian Islands have
formed as the Pacific Plate
moves across a hot spot.
Why is Plate Tectonics Important?
• Mineral Deposits: some minerals are
found at certain plate boundaries. Ex:
copper, lead and zinc are found in
rocks at convergent plate boundaries.
• Oil: subduction zones are ideal for the
formation of oil deposits.
• Natural Hazards: by understanding
how volcanoes and earthquakes occur,
many lives can be saved.