plate-tectonics-power-point.ppt

1. Plate Tectonics
The theory that the Earth’s outermost layer is
fragmented into a dozen or more large and
small plates that move relative to one another
as they ride on top of hotter, more mobile
material.

2. Earth has 3 compositional layers – crust, mantle, core
The major
features on
Earth’s
surface are
the result of
processes in
the upper few
hundred
kilometers
Earth’s Interior
USGS

3. Lithosphere
•Rigid layer
composed of crust
& uppermost mantle
•Divided into mobile
tectonic plates
Asthenosphere
•Weaker layer found
in upper part of
mantle
•Flows due to small
proportion (1%) of
melted minerals
Two key mechanical layers in crust and upper mantle
Earth’s Interior
USGS

4. What Are Tectonic Plates?
• A plate is a large, rigid slab of
solid rock.
– Plates are formed from the
lithosphere: the crust and the
upper part of the mantle.
• The plates “float” on the slowly
flowing asthenosphere: the
lower part of the mantle.
• The plates include both the
land and ocean floor.
• The Mohoriovicic discontinuity
or Moho is the boundary
between the crust and the
mantle.

5. What Drives Plate
Tectonics?
• The slow movement of hot,
softened mantle lies below
rigid plates.
• The hot, softened rock in the
mantle moves in a circular
manner in a convection flow
– the heated, molten rock
rises to the surface,
spreads, and begins to cool,
and then sinks back down to
be reheated and rises again.

6. Earth’s Plates

7. Movement of
the Plates
Over Time
Permian
248 million years ago
Triassic
206 million years ago
Jurassic
206 million years ago
Cretaceous
65 million years ago
Present Day

8. Progression
of Indian
Land Mass

9. What makes the plates move?
Convection Currents in the mantle move the plates as the core heats
the slowly-flowing asthenosphere (the elastic/plastic-like part of the
mantle).

10. Plate Boundaries

11. Different Types of
Boundaries

12. Different Types of
Boundaries
• Convergent boundaries come together
– Places where crust is destroyed as one plate dives under
another
• Divergent boundaries spread apart
– Places where new crust is generated as the plates pull away
from each other
– New crust is created from magma pushing up from the
mantle
• Transform boundaries slide against each other
– Places where crust is neither produced nor destroyed as
the plates slide horizontally past each other

13. How is the rock pushed at
convergent boundaries?
A plate boundary where two plates
move towards each other.
Boundaries between two
plates that are colliding
 
This stress is called COMPRESSION

14. Convergent Boundaries
• Places
where
plates
crash (or
crunch)
together or
subduct
(one sinks
under)

15. Oceanic-Continental
Convergence
• The oceanic plate subducts under the continental plate because it has lower
density.
• The oceanic Nazca Plate is being subducted under the continental part of
the South American Plate.
• The South American Plate is being lifted up, creating the Andes mountains.
• Strong, destructive earthquakes and rapid uplift of mountain ranges are
common in this region.
• These earthquakes are often accompanied by uplift of the land by as much
as a few meters.
• Mount Saint Helens is along the subduction zone of the Juan de Fuca plate
(an oceanic plate) and the North American plate (a continental plate).
Oceanic – Continental Convergence

16. Oceanic-Oceanic
Convergence
• When two oceanic plates converge,
one is usually subducted under the
other.
• An older oceanic plate is colder,
therefore more dense and less
buoyant, and will subduct under a
younger, hotter, less dense, and
more buoyant oceanic plate.
• In the process, a trench is formed.
– The deepest trenches in the
oceans are along oceanic-
oceanic subduction zones (i.e.,
the Marianas Trench in the
Pacific, which is deeper than
Mt. Everest is high).
• Subduction in oceanic-oceanic plate
convergence can result in the
formation of volcanoes.
• Examples of oceanic-oceanic
convergence are the arcuate chains
of islands in the southwest Pacific,
Japan, and the Aleutian Islands.
Oceanic – Oceanic Convergence

17. Continental-Continental
Convergence
Continental – Continental Convergence
• When two continents meet head-on,
neither is subducted because the
continental rocks are relatively light and,
like two colliding icebergs, resist downward
motion.
• Instead, the crust tends to buckle and be
pushed upward or sideways.
The collision between the Indian and
Eurasian plates has pushed up the
Himalayas and the Tibetan Plateau.

18. Continental-Continental
Convergence
• 50 million years ago, the
Indian Plate collided into the
Eurasian Plate.
• After the collision, the slow
continuous convergence of the
two plates over millions of
years pushed up the Himalaya
and the Tibetan Plateau to
their present heights.
• The Himalaya form the highest
continental mountains in the
world.

19. What happens when the rock is
squeezed from the Stress of
Compression?
• A REVERSE FAULT
• Rock is forced upward as it is
squeezed.

20. Helpful Hints…
• Convergent = “Connecting” boundaries
• May work like a trash compactor smashing
rock.
– Rock goes crunches up to make folded
mountains.
– Rock goes down “under” @ subduction zone.

21. Divergence
• Divergent boundaries occur
along spreading centers where
plates are moving apart and new
crust is created by magma
pushing up from the mantle.
• The Mid-Atlantic Ridge is a
divergent boundary.
• Sea-floor spreading over the
past 100 to 200 million years has
caused the Atlantic Ocean to grow
from a tiny inlet of water between
the continents of Europe, Africa,
and the Americas into the ocean
that exists today.

22. Divergent Boundaries
A plate boundary where two plates move away
from each other.
 
RIFTING
causes
SEAFLOOR SPREADING

23. How is the rock pulled at
Divergent Boundaries?
Rock gets THIN in the middle as it
is pulled apart.
This STRESS is called

24. What happens when the rock
SNAPS from the Stress of
Tension?
A Normal Fault (fault is a break in Earth’s
crust)
Rock drops down as it breaks

25. What happens next at Divergent
Boundaries?
• A geologic feature
or event…
May form RIFT
VALLEYS on
continents
SEA-FLOOR
SPREADING in the
ocean

26. Helpful Hints…
• Divergent is like “dissecting” or “dividing”
• If you pull warm bubble gum or silly putty,
it will thin in the middle until it is stressed
so much that it breaks.
• Happens on land
& under H2O

27. Features of Divergent
Boundaries
• Mid-ocean
ridges
• rift valleys
• fissure
volcanoes

28. Transform
• The zone between two plates that
slide
past one another is called a
transform-fault boundary, or
transform boundary.
• These large faults connect two
spreading centers or connect
trenches.
• Most transform faults are found on
the ocean floor.

29. Transform
• The San Andreas Fault is
one of the few transform
faults exposed on land.
– It connects the East
Pacific Rise, a divergent
boundary to the south, with
the Juan de Fuca Ridge, a
divergent boundary to the
north.
– Most earthquakes in
California are caused by
the accumulation and
release of strain as the two
plates slide past each
other.

30. Transform Boundaries
A plate boundary where two plates move past
each other in opposite direction.

31. How is the rock broken at Transform
Boundaries?
• Rock is pushed
in two opposite
directions (or
sideways, but
no rock is lost)
• This stress is
called
SHEARING

32. What happens when the rock is
sheared (or “cut”) from the Stress of
Shearing?
• A STRIKE-SLIP FAULT
• Rocks on each side of the fault slip
past each other as they break.

33. Helpful Hints…
• Shearing means cutting (“Shears” are like
scissors)
• Transform boundaries run like trains going
past each other in different directions &
they shake the ground!

34. What happens next at Transform
Boundaries?
• May cause
Earthquakes
when the rock
snaps from the
pressure.
• A famous fault
@ a Transform
Boundary is the
San Andreas
Fault in
California.

35. Consequences of Plate
Tectonics
• Earthquakes and volcanic activity are linked to plate
tectonic processes.
• The Ring of Fire is the most seismically and volcanically
active zone in the world.

36. Consequences of Plate
Tectonics
The San Andreas Fault – a
transform fault
Aerial view of the area around Thingvellir, Iceland,
showing a fissure zone (in shadow) that is an on-land
exposure of the Mid-Atlantic Ridge. Right of the fissure,
the North American Plate is pulling westward away from
the Eurasian Plate (left of fissure).

37. Consequences of Plate
Tectonics
The Aleutian Islands, an island arc The 1980 eruption of Mount
Saint Helens

38. Consequences of Plate
Tectonics
The convergence of the Nazca and South American Plates
has deformed and pushed up limestone strata to form
towering peaks of the Andes, as seen here in the
Pachapaqui mining area in Peru.
Helicopter view (in February 1994) of the active
lava lake within the summit crater of 'Erta 'Ale
(Ethiopia), one of the active volcanoes in the
East African Rift Zone.

39. Can you match
the boundary
name correctly
with its diagram?
A.____________
_
B.____________
_
C.____________
Plate Boundaries:

40. Plate Boundaries:
• Correct
Answers:
A.Divergent
B.Convergent
C.Transform

41. References
• Understanding Plate Motions. USGS.
http://pubs.usgs.gov/publications/text/unde
rstanding.html
• Plate Movement. OptIPuter Outreach.
http://education.sdsc.edu/optiputer/teacher
s/platemovement.html
• Plate Tectonics. The Way the Earth Works.
LHS GEMS, 2002.