Download plate tectonics

PLATE TECTONICS
Theory of Continental Drift, Plate Boundaries
This activity requires you to
discuss with a partner
Quick Review
**Discuss with your partner the definition of:
 Lithosphere
 Asthenosphere
 Plate
Tectonics
Quick Review

Lithosphere
 Crust
and the
upper part of the
mantle
 Broken
up in
rocky, rigid mass
called
LITHOSPHERIC
PLATES
Quick Review

Asthenosphere
 Top part of mantle
 Molten (melted)
 Fluid
Quick Review

Plate tectonics
Lithospheric plates move around SLOWLY on
the fluid asthenosphere
 At PLATE BOUNDARIES (where the plate
meet), plates interact in many ways
E.g. Collide (Bump into each other),
Diverge (Go away from each other), slide past
each other, go on top/ below one another

Theory of Continental Drift

Developed by
German
meteorologist
Alfred
Wegener
(1880-1930)
Theory of Continental Drift



Continents have not always
been at the present position,
but have “drifted” to these
locations over millions of years
All continents joint together to
form Supercontinents
Since Earth was formed,
supercontinentS have been
broken and formed MANY
TIMES
Theory of Continental Drift

PANGAEA “Pan”=all “Gaea”= World
Most recent supercontinent
 Formed 250 million years ago
 Started pulling part 200 million years ago
Evidence for Continental Drift
1. The Jigsaw Fits!
 Matching coastline of South America &
Africa
Evidence for Continental Drift
2. Matching Geological Structures and
Rocks
 Mountain ranges that begin in one
continent, end at coastline, and continue
across another continent
 Similarities in folds and rock ages in
different continents that are separated
Evidence for Continental Drift
3. Fossil Evidence
E.g. Mesosaurus
 Only found in 2 small
geographic regions (SE
South America and SW
Africa)
Evidence for Continental Drift
E.g. Glossopteris (Fern)
Found in small regions of
South America, Africa, India,
Antarctica, and Australia
Wegner wondered
how this is possible!
Evidence for Continental Drift
4. Glacier Evidence
Glacier Deposits are found in tropical places!!
(Glacier are big sheets of ice only found in cold weather)
Coal beds are found in Antarctica!!
(Coal is created by
decomposition of
tropical swamp)
Evidence of Continental Drift
Wegener’s Conclusion:
Continents were once
in completely different
position on Earth, and
have moved to their
present position
Rodina Supercontinent
(1.2 bya)
Theory of Plate Tectonics
Wegener’s Theory
of Continental
Drift has ONE
MAJOR
PROBLEM:
 He does not understand HOW the
continents moved.
Theory of Plate Tectonics
After Alfred Wegener died, oceanographer
discovered Mid-Atlantic Ridge
 Thin
mountain range under water (ocean
floor)
 Striped pattern found to either side of ridge
 Stripes alternate north and south polarity
Theory of Plate Tectonics
Discuss :
How was the Mid Atlantic Ridge formed?
So what does the Mid Atlantic Ridge prove (support)
Theory of Plate Tectonics
** Let’s look the Mid-Atlantic Ridge using
Google Earth**
*Ms. Yu will also show you a demo on
Mid-Atlantic Ridge** =)
Theory of Plate Tectonics
Plate Boundaries
-
-
Plates flow around due to
Convection Current in
asthenosphere
Radioactive materials
deep in the mantle create
hot areas (less dense)
Magma force to the
surface
Discuss: What are convection currents? (Science 8, 9?)
Plate Boundaries
**Discuss: How do you think plates can
interact with each other?
Divergent Plate Boundaries
Plates move away
from each other
Magma risepush old
material aside cool
become new
lithospheric material
 Forms Ocean
Ridges at
Spreading Centre
and Rifts (land)

RIFT
Convergent Plate Boundaries
1. OCEANIC-CONTINETAL COLLISION
Subduction Zone oceanic plate (more
dense) slides under continental plate
 Extra material from subduction plate is
melted off
 Trench formed
 Can form Volcanoes, Earthquakes &
Mountains

Convergent Plate Boundaries
At Subduction Zone, SLAB
PULL occurs
 The plate that is subducting is
actually pulling the rest of the
plate with it
 Slab pull adds to the force from
convection currents

Convergent Plate Boundaries
2. OCEANIC-OCEANIC
 Subductionone plate will be FORCED
under another
 Cause earthquakes
 Form Volcanoes and Island Arc (chains of
islands in the ocean formed from
convergent plates collisions)
E.g. Japan, Aleutian Islands (Alaska)
Convergent Plate Boundaries
3. CONTINENTALCONTINENTAL
COLLSION
 Plates collide,
crumble and folds
 Mountain Building
E.g. Mount Everest
in Himalayas
Transform Plate Boundaries


Plates slide past one
another, moving in
opposite directions
Produce large, shallow
earthquakes
E.g. San Andreas Fault
in California
(North American plate
sliding past Pacific
Plate)
Vancouver, British Columbia
** Discuss: What type of plate boundaries
do you think we are on right now?
Convergent: Oceanic- Continental Collision
 Juan de Fuca Plate (oceanic) subducts
under North American Plate (continental)
 Rocky Mountains, Cascade Mountain
volcanoes, Earthquakes
Google Earth

Volcano
RING OF FIRE
 Along edges of Pacific Ocean
 75% of the Earth’s active volcanoes
Volcano
COMPOSITE VOLCANOES
 Cone shape volcano
 Recurring eruptions (ash and lava) build
up to form strata
 Thick magma that trap gas explosive
eruptions
 Subduction zone
E.g. Mt. St. Helen (October 2004) Video
Mt. Garibaldi
Mt. Fuji, Japan
Volcano
E.g. Hawaiian
Volcanoes
SHIELD VOLCANO
 Form at HOT SPOT (weak part of plate where
molten material can burst through)
 Magma are more fluid
 Largest volcanoes on Earth!
Hawaiian Volcano- View of Crater
Volcano
RIFT ERUPTIONS
 Spreading centre or rifts at divergent
boundaries
 May produce lots of lava