Learning Plate Tectonic Geography

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Learning Plate Tectonic Geography

• Brushing up on basic geography will help you
  learn Plate Tectonics
• Once you know your basic geography (continents
  and major mountain ranges) and ocean basin
  features (Mid Ocean Ridges, Oceanic Trenches) you
  can
• Learn the 7 major plates
• Learn the types of plate boundaries
• Learn why those features are where they are

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I. Introduction (cont.)

• E. Forces shaping the Earth at the surface and
  from within
• 1. Surficial Processes Solar energy and gravity
  shaping the landscape
• 2. Internal Processes Internal energy and forces
  that buckle and break Earths crust

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If External Processes Only?
Mississippi River Delta

• Question
• If 550 million tons of rock are broken down and
  transported to the sea from the United States
  each year,
• Why has our continent not been worn flat after
  the billions of years of its existence and
• Why havent the oceans been filled in?

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Mississippi River Drainage Basin Erosion,
transport, deposition
Mississippi River Delta
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1. Surficial ProcessesResults of the External
Heat Engine

• Weathering
• Chemical and Mechanical Breakdown of ?solid rock
  into ?sediments
• Erosion
• Removal of rock and sediment from source by
  Gravity, wind, water, ice

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Surficial Processes (cont.)Results of the
External Heat Engine

• Transport over large distances by water, wind and
  ice.

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Surficial Processes (cont.)Results of the
External Heat Engine

• Deposition of large amounts of sediment in seas
  and oceans

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2. Internal Earth Processes Results of the
Internal Heat Engine

• Evidence of internal energy and forces working on
  our earth.
• Intricate landscapes
• Volcanoes
• Earthquakes
• Geothermal Gradients (deeper is hotter)

Another Question What is the source of all this
energy?
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3. Formation of Earth

• Birth of the Solar System
• Nebular Theory
• nebula compresses
• Flattening of spinning nebula and collapse into
  center to form sun
• Condensation to form planets, planetesimal, moons
  and asteroids during planetary accretion around
  4½ billion years ago
• (Meteorites are iron-rich and rocky fragments
  left over from planetary accretion)

http//www.psi.edu/projects/planets/planets.html
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Orion Nebula www.hubblesite.org
www.geol.umd.edu/kaufman/ ppt/chapter4/sld002.htm
www.psi.edu/projects/ planets/planets.html
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Formation of the Planets

• The mass of the center of the solar system began
  nuclear fusion to ignite the sun
• The inner planets were hotter and gas was driven
  away leaving the terrestrial planets
• The outer planets were cooler and more massive so
  they collected and retained the gasses hence the
  Gas Giants

Terrestrial Planets
Gas Giants
www.amnh.org/rose/backgrounds.html
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Differentiation of the Planets

• The relatively uniform iron-rich proto planets
  began to separate into zones of different
  composition 4.6mya
• Heat from impacts, pressure and radioactive
  elements cause iron (and other heavier elements)
  to melt and sink to the center of the terrestrial
  planets

The zones of the earths interior
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Further Differentiation of Earth

• Lighter elements such as Oxygen, Silicon, and
  Aluminum rose to form a crust
• The crust, which was originally thin and heavy
  (iron rich silicate) Like todays Oceanic crust,
• Further differentiated to form continental crust
  which was thicker, iron poor and lighter

Figure 1.7, the zones of the earths interior
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Composition of Earth and Crust
 
 
 
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Crust and MantleLithosphere and Asthenosphere

• The uppermost mantle and crust are rigid solid
  rock (Lithosphere)
• The rest of the mantle is soft but solid
  (Asthenosphere)
• The Continental Crust floats on the uppermost
  mantle
• The denser, thinner Oceanic Crust comprises the
  ocean basins

Figure 1.7, Detail of crust and Mantle
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Litho-spheric Plates

• The Lithosphere is broken into plates (7
  major, 6 or 7 minor, many tiny)
• Plates that ride around on the flowing
  Asthenosphere
• Carrying the continents and causing continental
  drift

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Plates Shown by Physiography
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Types of Plate Boundaries

• -Convergent -Divergent -Transform

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Lithospheric Plates and Boundary types
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Three Types of Plate Boundaries

• Divergent
• ??
• Convergent
• ??
• Transform
• e.g., Pacific NW

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Divergent Plate Boundaries

• Where plates move away from each other the
  iron-rich, silica-poor mantle partially melts and

• Extrudes on to the ocean floor or continental
  crust
• Cool and solidify to form Basalt

Lithosphere
Lithosphere
Simplified Block Diagram
Asthenosphere
Iron-Rich, Silica-Poor, Dense Dark,
Fine-grained, Igneous Rock
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Characteristics of Divergent Plate Boundaries

• Divergent Plate Boundary
• Stress Tensional ? extensional strain
• Volcanism non-explosive, fissure eruptions,
  basalt floods
• Earthquakes Shallow, weak
• Rocks Basalt
• Features Ridge, rift, fissures

Oceanic
Crust
Magma Generation
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Locations of Divergent Plate BoundariesMid-Ocean
Ridges
(Mid-Arctic Ridge)

• East Pacific Rise
• Mid Atlantic Ridge
• Mid Indian Ridge
• Mid Arctic Ridge
• Fig. 1.10

Mid-
Mid-Atlantic Ridge
East Pacific Rise
Indian
Ridge
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Divergent Plate Boundaries

• Rifting and generation of shallow earthquakes
  (lt33km)

0 33 70
0
30
150
70
150
300
300
500
500
800
Depth (km)
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E.g., Red Sea and East African Rift
Valleys
Fig. 2-16 Pg. 41
Fig. 2-15 Pg. 40

• Fig. 19.21
• Fig. 19.22

Thinning crust, basalt floods, long
lakes Shallow Earthquakes Linear sea, uplifted
and faulted margins
Rift Valley
Rift Valley
Oceanic Crust
Passive continental shelf and rise
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Convergent Plate Boundaries

• Where plates move toward each other, oceanic
  crust and the underlying lithosphere is subducted
  beneath the other plate (with either oceanic
  crust or continental crust)
• Wet crust is partially melted to form silicic
  (Silica-rich, iron-poor, i.e., granitic) magma
• Stress Compression
• Earthquakes
• Volcanism
• Rocks
• Features

Fig. 2-17 Pg. 42
Oceanic Trench
Volcanic Arc
Plate Movement
Lithosphere
Lithosphere
Subducted Plate
Magma Generation
Simplified Block Diagram
Shallow and Deep Earthquakes
Asthenosphere
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Convergent Plate Boundary e.g., Pacific Northwest

• Volcanic Activity
• Explosive, Composite Volcanoes (e.g., Mt. St.
  Helens)
• Arc-shaped mountain ranges
• Strong Earthquakes
• Shallow near trench
• Shallow and Deep over subduction zone

• Rocks Formed
• Granite (or Silicic)
• Iron-poor, Silica-rich
• Less dense, light colored
• Usually intrusive Cooled slowly, deep down, to
  form large crystals and course grained rock

Fig. 2-18 Pg. 42
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The Ring of Fire (e.g., current volcanic
activity)A ring of convergent plate boundaries
on the Pacific Rim

• New Zealand
• Tonga/Samoa
• Philippines
• Japanese Isls.
• Aleutian Island arc and Trench
• Cascade Range
• Sierra Madre
• Andes Mtns.
• Also Himalayans to the Alps

Composite Volcanic Arcs (Granitic,
Explosive) Basaltic Volcanism (Non-Explosive)
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Depth of Earthquakes at convergent plate
boundaries
Seismicity of the Pacific Rim 1975-1995
0 33 70

• Shallow quakes at the oceanic trench (lt33km)
• Deep quakes over the subduction zone (gt70 km)

150
300
500
800
Depth (km)
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Major Plates and Boundaries

• Each major plate caries a continent except the
  Pacific Plate.
• Each ocean has a mid-ocean ridge including the
  Arctic Ocean.
• Divergent bounds beneath E. Africa, gulf of
  California
• The Pacific Ocean is surrounded by convergent
  boundaries.
• Also Himalayans to the Apls

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Divergent Plate BoundariesRifting and Formation
of new Basiltic Oceanic Crust

• Oceanic Crust
• Thin (lt10 km)
• Young (lt200my)
• Iron Rich (gt5) /
• Silica Poor (50)
• Dense ( 3 g/cm3)
• Low lying (5-11 km deep)
• Formed at Divergent Plate Boundaries

Make a Comparison Table on a separate page

• Composite Volcanic Arcs (explosive)
• Basaltic Volcanism (non-explosive)

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Convergent Plate BoundariesFormation of Granitic
Continental Crust

• Oceanic Crust
• Thin (lt10 km)
• Young (lt200 my)
• Iron Rich (5) /
• Silica Poor (50)
• Dense (s.g. 3 x H2O)
• Low lying (5-11 km deep)
• Formed at Divergent Plate Boundaries

• Continental Crust
• Thick (10-50 km)
• Old (gt200 m.y. and up to 3.5 b.y.)
• Iron Poor (lt1) /
• Silica Rich (gt70)
• Less Dense ( 2.5 g/cm3)
• High Rising
• (mostly above see level)
• Formed at Convergent Plate Boundaries

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Isostatic Adjustment

• Why do we see,
• at the earths surface,
• Intrusive igneous rocks and
• Metamorphic rocks
• Formed many km deep?
• Thick, light continental crust buoys up even
  while it erodes
• Eventually, deep rocks are exposed at the
  earths surface
• Minerals not in equilibrium weathered
  (transformed) to clay
• Sediments are formed

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Transform Plate Boundaries

• Offset Mid- ocean ridges
• May cut continents
• e.g. San Andreas Fault

Fig. 2-21 Pg. 44
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The Hydrologic Cycle

• Works with Plate-Tectonics to
• Shape the land
• Weathering
• clay, silt, sand
• Erosion
• Transport
• Sedimentation
• Geologic Materials
• Sediments
• Sedimentary Rocks

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The 3 rock types form at convergent plate
boundaries

• Igneous Rocks When rocks melt, Magma is formed,
  rises, cools and crystallizes.
• Sedimentary Rocks All rocks weather and erode to
  form sediments (e.g., gravel, sand, silt, and
  clay). When these sediments accumulate they are
  compressed and cemented (lithified)
• Metamorphic Rocks When rocks are compressed and
  heated but not melted their minerals
  re-equilibrate (metamorphose) to minerals stable
  at higher temperatures and pressures

Sedimentary Rocks
Metamorphic Rocks
Igneous Rocks
Magma
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The RockCycle
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Igneous and Sedimentary Rocks at Divergent
Boundaries and Passive Margins

• Igneous Rocks (basalt) are formed at divergent
  plate boundaries and Mantle Hot Spots. New
  basaltic, oceanic crust is generated at divergent
  plate boundaries.
• Sedimentary Rocks are formed along active and
  passive continental margins from sediments shed
  from continents

• Sedimentary Rocks are formed on continents where
  a basin forms and sediments accumulate to great
  thicknesses. E.g., adjacent to mountain ranges
  and within rift valleys.

See Kehew, Figure 2.30