Plate Tectonics

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Plate Tectonics
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1. Basic components of earth
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2. Two layers key to plate tectonics

• LITHOSPHERE
• Hard brittle
• Crust upper mantle
• Plate

• ASTHENOSPHERE
• Plastic silly putty
• Lower mantle
• Convection current that carries the plates

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3. Most common rock in crust

• Silicon dioxide SiO2
• Found in magma or igneous rocks the most common
  rock

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4. How is convection like a lava lamp?
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Convection cells in asthenosphere
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5. Two types of crust
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Crust

• OCEAN crust
• Denser
• Thinner
• Eventually is subducted
• Relatively young

• CONTINENTAL crust
• Less dense
• Thicker
• Rarely/never subducted
• Oldest crust on Earth

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6. Evidence supporting Theory of Continental
Drift by Alfred Wegner
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Fit of S. America to Africa
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Fossil evidence
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Geological evidence
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What is evidence gathered after WW2 that lead to
Theory of plate tectonics ---- Seafloor
spreading---
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7. Theory of Plate Tectonics

• a.The plates move across the surface
• b.Current idea is that plates move because of
  convection cell motion under the crust in the
  upper levels of the mantle---plume theory
• c.3 kinds of plate boundaries are divergent,
  convergent and transform
• d.Topography (surface shape) of earth is formed
  by uplift and weathering/erosion
• e. Different from Alfred Wegneners Theory of
  Continental Drift ( he could not explain HOW
  they moved)

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8. IN plate tectonics the earth is broken into
major plates
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9. What impact does Plate tectonics have on Earth?

• Splitting of continents creates isolation ?
  opportunities for evolution (biodiversity)
• Uplift of mountains creates new air
  precipitation patterns ? new habitats
  (ecosystems)
• EQs destroy human constructionhabitation and
  hwys
• Volcanoes eruptions produce new land, rich soil

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10. The evidences that show how plates move?

• Magnetism
• Seafloor spreading
• Depth of marine sediments
• Ring of fire
• Comparing oceans
• Hawaiian hot spot

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A. Magnetic field lines

• While magma cools, it is imprinted with the
  magnetic field lines.
• Periodically the magnetic poles reverse
  directions. N becomes S S becomes N.
• New magma will be imprinted with the new magnetic
  field lines.

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Mirror image of stripes either side of spreading
zone
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Depth of marine sediments age of marine
sediments
Thin sediments by ocean ridge Thicker sediments
by trenches
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What kind of plate boundary is the Ring of Fire?

• A) diverging ocean plate
• B) converging ocean continental plates
• C) converging ocean ocean plates
• D) transform fault zone
• Whats the answer?

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Ring of Fire add this into notes

• Subduction zones around Pacific Ocean
• ? volcanoes
• ? major earthquakes

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Hawaiian Hot spot
What is does this show us? Which is the youngest
and oldest island?
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Comparing Oceans

• Pacific Ocean is shrinking
• Subduction zones
• Oldest sediments are farthest from spreading zone

• Atlantic Ocean is widening
• Spreading zones
• Oldest sediments are farthest from spreading zone

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11. 3 types of Plate Boundaries

• 1) diverging, spreading plates
• 2) collision, colliding, converging plates
• 3) sliding beside, transform faults

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Guess!!
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Divergent boundary

• As the crust separates, the gap is filled in with
  basalt.
• There may hydrothermal vents
• There may be a ridge
• Overall the crust is young in this region

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Diverging Zones aka spreading center

• CONTINENT
• Rift zone
• Valley w/ basalt flows
• E.g. Red Sea, Rift Valley in Africa

• OCEAN
• Creates new ocean floor
• Mounds of basalt
• E.g. Mid-Atlantic Ridge, East Pacific Rise

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Convergent Ocean-Continent

• Denser ocean crust is subducted under
• Deep trench, strong earthquakes
• Volcanic Mt range on continent
• E.g. Andes Mts, Cascade Mts

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Guess!!
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Convergent Continent-Continent

• Piles piles of crumpled, folded crust tall
  mountains
• Thick crust, earthquakes
• E.g. Himalayan Mts, Appalachian Mts, Alps

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Convergent Ocean-Ocean

• Slower plate is subducted under
• Deep trench, strong earthquakes, tsunamis
• Volcanic island archipelago
• E.g. Aleutian Islands, Japanese Islands,
  Indonesian Islands, Caribbean Islands

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Transform Faults

• 2 plates sliding beside each other
• Valleys, roads, fences offset
• Lots of earthquakes
• E.g. San Andreas Fault, Mendocino Fracture zone

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Right-transform Fault
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Just a reminder

• California will not fall into the sea.
• California is being divided into 2 pieces.
• So. Calif is traveling northwesterly towards
  Alaska on the Pacific Plate

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Transform Faults

• Permit differential spreading over the spherical
  shape of Earth

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12.earthquakes
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EQ seismic event

• A movement in earths crust that generates energy
• EQ are caused by movement of a fault

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Seismic Waves- p, s, l waves
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Offset road
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Offset stream, Carrizo Plain
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13. How to find an epicenter

• The interval between P and S is used to determine
  the distance from an epicenter.
• 3 s-p and 3 locations.

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Triangulation
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14. How they measure EQ

• Mercalli scale
• Measure the amount of ground shaking or local
  damage

• Richter Scale
• Measure the energy release from a seismic event
• The number on the Richter scale goes up
  exponentially. Meaning that a 2 one the Richter
  scale would be a 100, a 3 one the Richter scale
  would be a 1000 and so on. So a 6 is 1 000 000
  while a 5 is 100 000 so it is ten times the
  power.

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15. Lava flows
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fissure

• a crack in the crust
• Eg. Iceland

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Hot Spot

• A weak point near middle in the crust where lava
  erupts
• E.g. Hawaiian Islands

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Global volcanic hot spots
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Types of Volcanos
Shield volcano Cinder cone Composite volcano
Huge, shallow sided cones Form from fast, thin lava Non explosive No gas pressure Flows like ketchup Divergent or hot spot Ex. Hawaiian islands or iceland Small steep sided cone thicker and slower Rhyolite tends plug the cone and build up pressure Mid sided cone alternating lava and sediment layers Mixture lava such as andesite A lot gas pressure Very explosive Subduction Ex Mt. St Helens
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Tsunami

• caused by EQ in or near ocean
• Tidal waves are caused by storms like hurricanes
• Satellite buoy for people in low lying areas

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The End

• Of Plate Tectonics Presentation