Theory of Plate Tectonics

1
(No Transcript)
2
Questions...

• What is the theory of plate tectonics?
• What is the lithosphere?
• What is the asthenosphere?
• What is the connection between the two?
• What are the two types of plates?

3
The Earth Has 3 Major Layers
Core Inner Outer Mantle Crust
(Mantle) Asthenosphere Lithosphere Core Link
click here for book
4
Layers
5
The Crust

• The temperatures of the crust is 1600 degrees
  Fahrenheit (870 degrees Celsius) in the deepest
  parts of the crust.
• Composed mostly of oxygen, silicon, and aluminum
• The seven continents and ocean plates basically
  float across the mantle which is composed of much
  hotter and denser material.

6
What is the Lithosphere?

• The crust and part of the upper mantle
  lithosphere
• 100 km thick
• Less dense than the material below it so it
  floats
• Continental Crust granite
• Oceanic Crust - Basalt

7

• The oceanic crust consists of a volcanic lava
  rock called basalt. Basaltic rocks of the ocean
  plates are much denser and heavier than the
  granite rock of the continental plates.
• Because of this the continents ride on the denser
  oceanic plates.

8

• The crust and the upper layer of the mantle
  together make up a zone of rigid, brittle rock
  called the Lithosphere.
• The layer below the rigid lithosphere is a zone
  of asphalt-like consistency called the
  Asthenosphere.
• The asthenosphere is the part of the mantle that
  flows and moves the plates of the Earth.

9
2 Types of Plates

• Ocean plates - plates below the oceans
• Continental plates - plates below the continents

10
What is Plate Tectonics?

• The theory that the Earths lithosphere is
  divided into plates that move on top of the
  asthenosphere.
• The Earths crust and upper mantle are broken
  into sections called plates
• Plates move around on top of the mantle like
  rafts
• Plates move along smoothly but sometimes they
  stick and build up pressure. The pressure builds
  and the rock bends until it snaps. When this
  occurs and Earthquake is the result!

11
Plate Tectonics
The Earth is divided into layers due to
differences in density. These differences are
caused by differences in composition,
temperature, and pressure.
12
Plate Tectonics

• Theory of Continental Drift continents drift
  apart from one another and have done so for
  years.

13
The Theory of Continental Drift
14
Continental Drift Theory

• Proposed by Alfred Wegener in 1912
• 250 million years ago, all of the continents were
  combined into one super-continent called Pangea
  
• The continents gradually drifted apart to where
  they are today

15
Pangaea

• Pangaea was a time when all land masses on Earth
  were once together as all earth
• Panthalassa was the sea that surrounded all the
  land all sea
• Pangaea Link

16
About 180 Million Years Ago
17

• Laurasia was the northern part of Pangea composed
  of N. America and Eurasia
• Gondwana was the southern part of Pangea composed
  of the remaining continents.

18
135 Million Years Ago

• About 135 million years ago Laurasia was still
  moving, and as it moved it broke up into the
  continents of North America, Europe and Asia
  (Eurasian plate).
• Gondwanaland also continued to spread apart and
  it broke up into the continents of Africa,
  Antarctica, Australia, South America, and the
  subcontinent of India.
• Arabia started to separate from Africa as the Red
  Sea opened up.
• The red arrows indicate the direction of the
  continental movements.

19
Evidence of Continental Drift

• Shapes of continents fit like a puzzle
• Matching fossils found on different continents
• Matching rock formations in Africa and S. America
• Glacier patterns

20
The Same Plant and animal Fossils found on
different coastlines.
21
Same rock patterns found in South America, India,
Africa, Antarctica and Australia
22
Ancient Climates

• Tropical plant remains (coal deposits) found in
  Antarctica
• Glaciation in Africa, South America, India, and
  Australia during the same time

23
Supporting Evidence

• Many years later (1950s-1960s) new evidence
  provided better support like
• Earthquake belts
• Locations of volcanoes
• Magnetic reversal showed in igneous rocks on the
  ocean floor, Mid-Ocean Ridge

24
Mid-Ocean Ridge

• Seafloor Spreading click here for link and then
  show Magnetic Reversal after seafloor spreading.

25

• Iceland straddles the Mid-Atlantic Ridge, and
  offers a natural laboratory for studying on land
  the processes that occur along the submerged
  parts of the Mid-Atlantic Ridge.

Splitting along the N. American and Eurasian
Plates as N. America moves westward relative to
Eurasia.
26
Lava fountains (10 m high) spouting from eruptive
fissures during the October 1980 eruption of
Krafla Volcano. (Photograph by Gudmundur E.
Sigvaldason, Nordic Volcanological Institute,
Reykjavik, Iceland.)
27
Aerial view of the area around Thingvellir,
Iceland, showing a fissure zone (in shadow) that
is the 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 the fissure). Large building (near
top) marks the site of Lögberg, Iceland's first
parliament, founded in the year A.D. 930.
(Photograph by Oddur Sigurdsson, National Energy
Authority, Iceland.)
28
More Interesting Stuff!

• Developing the theory This Dynamic Earth, USGS
• Also read magnetic striping and polar reversal,
  and seafloor spreading.

29
Convection Currents the reason why plates move!

• Causes of Tectonic Movement click here for
  interactive link.

30
Types of Plate Boundaries Convergent,
Divergent, Transform click here for interactive
book.
31
Diverging Plates

• Diverging Plate Boundary is where the seafloor
  spreads.

• Two plates moving in opposite directions

32
Divergent Boundaries

• Boundary between two plates that are moving apart
  or rifting
• ? ?
• RIFTING causes Seafloor Spreading, Fissure
  Volcanoes, Rift Valleys

33
Diverging Boundarycontinent / continent

• Rifting happens as they pull apart
• Rift valleys and seas form
• Great African Rift, Red Sea, Baja California

34
Convergent Boundaries

• Boundaries between two plates that are colliding
• ? ?
• There are 3 types
• Ocean/Ocean
• Continent/Continent
• Continent/Ocean

35
Converging Boundary - ocean/ocean

• Subduction more dense plate slides under the
  less dense plates
• Forms trenches and volcanic island arcs
• Aleutian Islands, Mariana Islands, Mariana Trench
  (deepest)

36
Where does the Krakin Live?

• Most likely in the Trenches!
• These are the deepest parts of the ocean floor
  and are created by subduction!
• http//blindkat.hegewisch.net/pirates/Nautical_Myt
  hs.htmldjl

37
Converging- continent/ocean

• Subduction
• Forms trenches and volcanic mtn. ranges
• Peru-Chile Trench (longest), Andes Mtns.

38
Peru-Chile Trench
Nazca Plate
South American Plate
Off the coast of South America along the
Peru-Chile trench, the oceanic Nazca Plate is
pushing into and being subducted under the
continental part of the South American Plate. The
South American Plate is being lifted up, creating
the towering Andes mountains. Strong, destructive
earthquakes and the rapid uplift of mountain
ranges are common in this region. The Nazca Plate
is sinking smoothly and continuously into the
trench, the deepest part of the subducting plate
breaks into smaller pieces that become locked in
place for long periods of time before suddenly
moving to generate large earthquakes. Such
earthquakes are often accompanied by uplift of
the land by as much as a few meters.
39
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.
(Photograph by George Ericksen, USGS.)
40
Holy Cow !!!
On June 9, 1994, a magnitude-8.3 earthquake
struck about 320 km northeast of La Paz, Bolivia,
at a depth of 636 km. This earthquake, within the
subduction zone between the Nazca Plate and the
South American Plate, was one of deepest and
largest subduction earthquakes recorded in South
America. Fortunately, even though this powerful
earthquake was felt as far away as Minnesota and
Toronto, Canada, it caused no major damage
because of its great depth
41
Converging- continent/continent

• Collision zones where folding and thrust fault
  mountains form
• Himalayan Mtn (tallest), Appalachian Mtns (oldest)

42
(No Transcript)
43
Convergence of Continent to Continent
                                       The
collision between the Indian and Eurasian plates
has pushed up the Himalayas and the Tibetan
Plateau.
44
Before and After
Cross sections showing the meeting of these two
plates before and after their collision. The
reference points (small squares) show the amount
of uplift of an imaginary point in the Earth's
crust during this mountain-building process.
45
Wild Beast of the Himalayas
46
Transform Boundaries

• Boundary between two plates that are sliding past
  each other
• EARTHQUAKES along faults
• Most are found under the ocean floor.

47
Transform Boundary

• Zones between two plates sliding horizontally
  past one another.

48
Transform Boundary
    The Blanco, Mendocino, Murray, and Molokai
fracture zones are some of the many fracture
zones (transform faults) that scar the ocean
floor and offset ridges. The San Andreas is one
of the few transform faults exposed on land. This
fault moves approx. 5 cm/yr.
49
San Andreas Fault, California

• Pacific plate moving NW with respect to the North
  American plate

50
Good-bye California ?
The San Andreas fault zone, which is about 1,300
km long and in places tens of kilometers wide,
slices through two thirds of the length of
California. Along it, the Pacific Plate has been
grinding horizontally past the North American
Plate for 10 million years, at an average rate of
about 5 cm/yr. Land on the west side of the
fault zone (on the Pacific Plate) is moving in a
northwesterly direction relative to the land on
the east side of the fault zone (on the North
American Plate).
51
(No Transcript)
52
Questions...

• What are the three types of boundaries?
• What direction do plates move at each boundary?
• Which boundaries have a subduction zonewhat
  occurs at a subduction zone?

53
Questions...

• What causes plates to move?
• How is a convection current formed?