Download Dynamic Crust 4 Plate Tectonics

Plate Tectonics
Wegener’s Continental Drift

The proposition first published in 1912.
 Continents
can shift positions around the globe.
 Continents
were once joined together to form one
landmass.

Supercontinent PANGAEA
Breakup of Pangaea
Breakup of Pangaea
Evidence for Wegener’s Continental Drift

Jigsaw Puzzle


Rock Layers


Edges of Continents fit together like puzzle
Similarities of rock layers and structures on opposing shores
of Atlantic
Fossil Correlation

Glossopteris plant leaf fossils found in Southern Africa,
Australia, South America, India, and Antarctica

Mesosaurus dinosaur fossils found in both South America and
Southern Africa
Evidence for Wegener’s Continental Drift
Jigsaw Puzzle
Evidence for Wegener’s Continental Drift
Matching Mountain Ranges and Glaciers
Evidence for Wegener’s Continental Drift
Fossil Correlation
Plate Tectonics Theory

Widely accepted theory for plate
movement in scientific community.
 Earth’s
lithosphere is broken up into rigid sections
called plates.
 The movement and interaction of these plates
cause major changes in Earth’s surface.
 Plates can move horizontally and vertically.
 Plates move due to floating on the
asthenosphere.
 Continents move as the plates they are
attached to move.
Mantle Convection
Scientists generally agree that mantle
convection is the basic driving force for
plate movement.
Convective flow is the motion of matter resulting
from changes in temperature.
Plate tectonics is a density driven process.
The molten rock is less dense than the
surrounding rock.
Mantle Convection
Mantle Convection
Mantle Convection Models
Convection and Tectonics
Continents and the Plates to which
they are attached
Tectonic Plates and Boundaries ESRT p. 5
Plate Tectonics
Types of Plate Boundaries
 Divergent boundaries (also called
spreading centers) are the place where two
plates move apart.
 Convergent boundaries form where two
plates move together.
 Transform fault boundaries are margins
where two plates grind past each other
without the production or destruction of the
lithosphere.
Three Types of
Plate Boundaries
Divergent Plate Boundaries –
Spreading Centers
plates move apart
 magma rises from below to fill gap and
push plates away from each other
 occurs at the mid-ocean ridges and at
continental rifts
 creates new basaltic ocean crust (dense)
at the ridge
 the oldest basaltic ocean crust is at the
edge of the continents – see diagram

Spreading Center
Divergent Boundary
Youngest
Oceanic
Crust
Oldest
Oceanic
Crust
Mid-Ocean Ridges
The mid-ocean ridge is a mountain
range at the bottom of the ocean that is
composed mainly of volcanoes and lava
flows. See map p. 5 ESRT
 The rocks created at the mid-ocean ridge
have magnetic minerals that are aligned
with Earth’s magnetic field.
 Earth’s magnetic field reverses polarity on
a cycle of thousands of years.

Testing Plate Tectonics
Evidence for Plate Tectonics
 The discovery of strips of alternating
polarity, which lie as mirror images across
the ocean ridges, is among the strongest
evidence of seafloor spreading.
Polarity of the Ocean Crust
Magnetic Striping of the Ocean Floor
Actions at Plate Boundaries
Transform Fault Boundaries
 At a transform fault boundary, plates grind
past each other without destroying the
lithosphere.
 Transform faults
• Most join two segments of a mid-ocean ridge.
• At the time of formation, they are roughly parallel
to the direction of plate movement.
• They aid the movement of oceanic crustal
material.
Transform Fault Boundary
Actions at Plate Boundaries
Convergent Boundaries
 Oceanic-Oceanic
• Two oceanic slabs converge and one descends
beneath the other.
• This kind of boundary often forms volcanoes on
the ocean floor.
• Volcanic island arcs form as volcanoes emerge
from the sea.
• Examples include the Aleutian, Mariana, and
Tonga islands.
Oceanic-Oceanic
Convergent Boundary
Actions at Plate Boundaries
Convergent Boundaries
 Continental-Continental
• When subducting plates contain continental
material, two continents collide.
• This kind of boundary can produce new
mountain ranges, such as the Himalayas.
Continental-Continental
Convergent Boundary
Collision of India and Asia
Actions at Plate Boundaries
Convergent Boundaries
 A subduction zone occurs when one
oceanic plate is forced down into the
mantle beneath a second plate.
 Oceanic-Continental
• Denser oceanic slab sinks into the asthenosphere.
• Pockets of magma develop and rise.
• Continental volcanic arcs form in part by volcanic
activity caused by the subduction of oceanic
lithosphere beneath a continent.
• Examples include the Andes, Cascades, and
the Sierra Nevadas.
Oceanic-Continental
Convergent Boundary
Tectonic Settings and Volcanic Activity
The Ring of Fire
Passive Continental Margin

5 main features
Coast – edge of continent
2. Continental Shelf – wide shallow extension of
continent
3. Continental Slope – steepest gradient drop toward
ocean floor
4. Continental Rise – collection of sediment from
turbidity currents
5. Abyssal plain – ocean floor, flattest places on Earth
1.
Passive Continental Margin – simple
Trailing Edge of Continent
Passive Continental Margin – detailed
Trailing Edge of Continent
Active Continental Margin
Subduction Zone

Subduction is the sinking of the denser
crust out of the two plates that are
colliding. See map p. 5 ESRT

Ocean trenches are the deepest parts of
the oceans.
 created
at subduction boundaries by bending
down of the subducting plate and warping of
the crust
Active Continental Margin
Subduction Zone

Continental Volcanic Arcs form on the
edge of the continental plate due a
combination of factors:
1.
Friction between plates


2.
3.
Subducting slab
Overriding slab
Increased temperature at depth
Lower density magma rises through denser solid
rock
Active Continental Margin
Continental Margins of the US
Volcanoes

created at subduction boundaries due to the
melting of the subducting plate at great depth

the rock becomes magma and rises because it is now
less dense than the surrounding rock

continental volcanic arcs form on the edge of a
continent that the plate is subducting beneath


Examples: Andes in South America, Cascades in United States
volcanic island arcs form on a plate boundary
where an oceanic plate is colliding with another
oceanic plate and the denser (older) plate is
subducting below the less dense (younger) plate

Example: Mariana, Aleutian, and Tonga Islands
Anatomy of a “Typical” Volcano
Hot Spots

are areas where intraplate volcanism
occurs.
 where
a mass of hotter than normal mantle
material called a mantle plume rises toward
the surface
 Examples:
Hawaiian Islands, Yellowstone, Iceland,
Canary Islands
 See Tectonic Plates p. 5 ESRT
Hawaiian Hot Spot
Hot Spot Volcano Tracks