Transcript Plate Tectonics

http://www.geophysics.rice.edu/plateboundary/
Where are the Earth’s tectonic plates and
their boundaries?
What happens at plate boundaries?
How do Earth scientists classify plate
boundaries?
Part 1.
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Identify the patterns of your area of expertise –
volcanology, seismology, geography, geochronology
- AT PLATE BOUNDARIES
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Describe what you observe – do not interpret what
you see, just describe the patterns
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Use descriptive terms: Wide or narrow, straight or
curved, symmetric or not symmetric, deep or
shallow, ridge or valley, active or inactive
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Identify 3-5 boundary types; color each on your
transparency; define in words
Part 2.
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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
Part 3.
 Describe
 What
the different types of boundaries
patterns were related in the different
data sets?
 What
skills did you
use in undertaking
this activity?
 Historical
use …
 How
might you use
it in your
classroom?

What might you
modify?
Plate Boundaries
Where Stuff Happens
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
Compositional
Crust - 2
Mantle
Core
Physical / Mechanical
Lithosphere
Asthenosphere
Mesosphere
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Two types of crust:
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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
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Oceanic crust
• Basalt - Mg, Fe (heavier
materials - relatively)
• 5-10 Km thick
• 200 Ma oldest; 100 Ma average
• Ophiolites
Crust
(Compositional)
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Lithosphere
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Asthenosphere
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PLATES in Plate Tectonics
Upper 200 km
Crust and upper mantle
Rigid
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
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Also hot; strong due to pressure
Lithosphere /
Asthenosphere
(Mechanical)
3 Basic
Boundary
Interactions
5 to 6 Basic
Boundary
Types
1. Divergent Boundaries
•Volcanic activity in fissures, some volcanos
•Shallow earthquakes, on plate boundary
•Young crust, symmetrical around boundary
•Ridge
•Rocks?
MidAtlantic
Ridge
Nazca Plate
South American Plate
Antarctic Plate
Andes Mountains
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
Foreshadowing …
Many on Earth
Relatively small … but mighty …
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
Eurasian Plate
Indian Plate
Himalaya Mountains
Tibetan Plateau
Himalayan Mtns.
Mt. Everest
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
Eurasian
Plate
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?
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
What’s Driving
Plate Tectonics
on Earth?
Mantle
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85% volume of Earth
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Density - 3.3 - 5.5 g/cm3
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Probably material such as Peridotite
(lots of heavy olivine - Fe, Mg)
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Solid; high pressure  slow,
creeping, viscous movement convection
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Samples from kimberlites, xenoliths
in volcanic eruptions, basalt
composition; lab experiments
Core
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15% of Earth’s volume / ~half of
diameter of Earth
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Outer core
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Molten
Density of pure iron or nickel/iron;
~2x density of mantle
Convection … Earth’s magnetic
field
Inner core
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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)
Earth’s Magnetic Field
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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
What’s Driving
Plate Tectonics
on Earth?
How Did Earth (and other planets) Get Layers?