NOTES
Links to summaries of key issues for each topic
VISUALS
Links to images employed in lectures
TEXT
Link to chapter outlines at online learning center
NOTES
Links to summaries of key issues for each topic
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Notes on Topic:
- The notes identify the learning
objectives within dominant themes
- They present summaries of key
issues for each topic
- They emphasize the terminology
used to describe the various phenomena.
2. Movement
of Continents:
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Learning Objectives:
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- Movement of continents and isostasy linked to mantle
convection.
- Magnetic anomalies arising from formation of oceanic
crust.
- Recognition of types of plate boundaries: divergent,
convergent, transform.
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Continental Drift
:
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- Ancient configuration known as Gondwanaland (Edward
Suess)
- Continental drift proposed by Alfred Wegener:
- continents 'fit' together as supercontinent Pangaea
- supported by fossil relationships
- separated driven by gravitation forces, an unsatisfactory
mechanism
- 1950's knowledge base of characteristics of ocean floor
- possesses mid-ocean ridge and rise, with central
rift
- trenches recognized
- In 1960's model advocated Harry Hess
- crust formed at mid-ocean ridges by "sea-floor spreading"
- crust consumed at trenches (subduction zones)
- movement driven by heat convection in the mantle
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Crustal Motion
:
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- Location of earthquakes
- typically linear belts
- greater depths in subduction zones
- Magnetic reversals:
- explained by Vine and Matthews
- series of magnetic anomalies
- caused by reversals of Earth's magnetic field
- Magnetic patterns (parallel stripes) on ocean floor
- record Earth's magnetic field when rocks cool
- irregular series of polarity reversals, like tape
recorder
- stripes are mirror images about ridge axis, older
away from ridge
- Polar wandering - paleomagnetic pole positioning
- position of magnetic pole helps confirm ancient
plate positions.
- Used to track plate movements.
- Oldest oceanic crust ~180Ma
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Plate Tectonics
:
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- Physical behavior of crust rationalized by J. Tuzo
Wilson and Dan McKenzie
- Plates: defined by boundaries of earthquake activity
into 3 types
- Divergent:
- spreading, extensional at mid-ocean ridges
- underwater eruptions of pillow lavas (basalts)
- basins expand as new crust forms, like conveyor
belt
- gradually crust cools, becomes denser, thickens
and sinks
- Convergent:
- colliding, compressive
- create trenches and mountain belts
- ocean crust descends back to mantle in subduction
zones
- Transform:
- sliding, slipping motion
- transform faults created by lateral displacement
- necessary result of plate movement on the surface
of a sphere
- linked to axis of plate rotation
- accommodates different rotation speeds
- forms vertical displacements or escarpments
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Department of Geological Sciences,
1001 E. Tenth Street, Bloomington, IN 47405-1403
Phone: (812) 855-5582 Last updated: 26 September 2002
Comments: simon@indiana.edu
Copyright
2002, The Trustees of Indiana University
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