Historical Geology

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http//www.geophysics.rice.edu/plateboundary/ Wh
ere are the Earths tectonic plates and their
boundaries? What happens at plate
boundaries? How do Earth scientists classify
plate boundaries?
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Part 1.

• Identify the patterns of your area of expertise
  volcanology, seismology, geography, geochronology
  - AT PLATE BOUNDARIES
• Describe what you observe do not interpret what
  you see, just describe the patterns
• Use descriptive terms Wide or narrow, straight
  or curved, symmetric or not symmetric, deep or
  shallow, ridge or valley, active or inactive
• Identify 3-5 boundary types color each on your
  transparency define in words

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Part 2.

• Bring together areas of expertise volcanology,
  seismology, geography, geochronology
• Correlate your data sets what collective
  patterns emerge?
• Identify 3-5 boundary types color each on a
  master transparency define in words

• 10 min
• 10 min

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Part 3.

• Describe the different types of boundaries
• What patterns were related in the different data
  sets?

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• What skills did you use in undertaking this
  activity?
• Historical use
• How might you use it in your classroom?
• What might you modify?

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Plate BoundariesWhere Stuff Happens
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Plate Tectonics Theory

• The upper mechanical layer of Earth (lithosphere)
  is divided into rigid plates that move away,
  toward, and along each other
• Most (!) geologic action occurs at plate
  boundaries in DISTINCT patterns

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Compositional Crust - 2 Mantle Core
Physical / Mechanical Lithosphere Asthenosphere Me
sosphere
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Crust(Compositional)

• Two types of crust
• Continental
• 30 of crust
• Granites and Diorites - rich in silicates and
  feldspars (lighter materials)
• 40 Km thick
• Oldest is 3.8 billion years (90 solar system
  age missing 700 m.y.)
• 4.4 billion year old zircons in Western Australia
• Oceanic crust
• Basalt - Mg, Fe (heavier materials - relatively)
• 5-10 Km thick
• 200 Ma oldest 100 Ma average
• Ophiolites

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Lithosphere / Asthenosphere(Mechanical)

• Lithosphere
• PLATES in Plate Tectonics
• Upper 200 km
• Crust and upper mantle
• Rigid
• Asthenosphere
• 200 km to 700 Km
• Upper mantle
• Hi temperatures / high pressure little strength
  ductile / plastic - NOT A LIQUID!
• Plates moving on this
• Magma generation
• Mesosphere
• Also hot strong due to pressure

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3 Basic Boundary Interactions 5 to 6 Basic
Boundary Types
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1. Divergent Boundaries

• Volcanic activity in fissures, some volcanos
• Shallow earthquakes, on plate boundary
• Young crust, symmetrical around boundary
• Ridge
• Rocks?

Mid- Atlantic Ridge
North American Plate
Eurasian Plate
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Nazca Plate
South American Plate
Antarctic Plate
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Andes Mountains
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2. Convergent Boundaries (a) Ocean-continent
convergence

• Volcanos tight, parallel boundary, landward
• Shallow to deep earthquakes
• Age varies on one side of the boundary not
  symmetrical
• Trench, mountain chain
• Rocks?

Andes Mountains
Peru-Chile Trench
South American Plate
Nazca Plate
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Foreshadowing Many on Earth Relatively small
but mighty
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2. Convergent Boundaries (b) Ocean-ocean
convergence

• Volcanos tightly spaced, parallel boundary, arc
• Shallow to deep earthquakes
• Age varies on one side of the boundary not
  symmetrical
• Trench, volcanic island chain
• Rocks?

Mariana Islands
Marianas Trench
Philippine Plate
Pacific Plate
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Eurasian Plate
Indian Plate
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Himalaya Mountains
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Tibetan Plateau
Mt. Everest
Himalayan Mtns.
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2. Convergent Boundaries (c) Continent-continent
convergence

• Volcanos rare, dispersed
• Shallow (to medium) dispersed earthquakes
• No age data
• High mountain chain
• Rocks?

Himalayan Mountains
Tibetan Plateau
Indian-Australian Plate
Eurasian Plate
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3. Transform-Fault Boundaries

• Volcanos dispersed, most on one side
• Earthquakes complex, shallow (to medium) on both
  sides
• Age data not symmetrical, one side of boundary
• Complex topography, wide mountains and basins
• Rocks?

Pacific Plate
North American Plate
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Plate Tectonics

• The upper mechanical layer of Earth (lithosphere)
  is divided into rigid plates that move away,
  toward, and along each other
• Most (!) geologic action occurs at plate
  boundaries in DISTINCT patterns

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Whats Driving Plate Tectonics on Earth?
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Mantle

• 85 volume of Earth
• Density - 3.3 - 5.5 g/cm3
• Probably material such as Peridotite (lots of
  heavy olivine - Fe, Mg)
• Solid high pressure ? slow, creeping, viscous
  movement - convection
• Samples from kimberlites, xenoliths in volcanic
  eruptions, basalt composition lab experiments

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Core

• 15 of Earths volume / half of diameter of
  Earth
• Outer core
• Molten
• Density of pure iron or nickel/iron 2x density
  of mantle
• Convection Earths magnetic field
• Inner core
• Solid (very hot, but higher pressure than outer
  core)
• Density of nickel/iron (13 g/cm3)
• Conducts heat - cooling
• Size of Moon (70 of Moon)

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Earths Magnetic Field

• Magnetic dipole a bar magnet tilted 11 degrees
• Generated by eddies in the conductive liquid of
  the outer core currents create magnetic fields
• Changes over time north magnetic pole wanders,
  north and south reverse
• Rather important to life really important to
  geology

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Whats Driving Plate Tectonics on Earth?
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How Did Earth (and other planets) Get Layers?