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Transcript
Plate Tectonics
theory that describes the formation,
movement, and interactions of lithosphere
sections that move over the athenosphere
Updated
Created by C. Ippolito
April 2009
Early Ideas About Plate
Movements
• 1596
– Dutch mapmaker suggested Africa and South
America may have been one continent
• 1912 Alfred Wegener
– Continental Drift
• hypothesis that continents had drifted or
moved
– Mesosaurus found eastern S.A. &
western Africa
– rock formations matchup
• Pangea
– single “super continent”
Updated
Created by C. Ippolito
April 2009
Permian Era (225 mya)
Updated
Created by C. Ippolito
April 2009
Triassic (200 mya)
Updated
Created by C. Ippolito
April 2009
Jurassic (135 mya)
Updated
Created by C. Ippolito
April 2009
Cretaceous (65 mya)
Updated
Created by C. Ippolito
April 2009
Present Day
Updated
Created by C. Ippolito
April 2009
Theory of Plate Tectonics
• Capt. H. H. Hess
– believed Wegener
– echo soundings of ocean floor
• mapped midocean ridges
– younger rocks at “rifts”
– older rocks on sides
– presented sea floor spreading mechanism
(1960’s)
– located deep sea trenches
• continental mtns (Andes)
• island arcs (Japan, Aleutians)
Updated
Created by C. Ippolito
April 2009
Other Evidence for Plate Tectonic
Theory
•
•
•
•
Updated
Worldwide distribution of volcanoes
Worldwide distribution of earthquakes
Age of rocks at rifts
Paleomagnetic “stripes” are symmetrical
about ridges – confirming seafloor
spreading
Created by C. Ippolito
April 2009
Basic Concepts
• Lithosphere (upper mantle + crust)
– made of rigid plates
• Plates move slowly
• Geologic activity at or near boundaries
• Interior of plates “quiet”
Updated
Created by C. Ippolito
April 2009
Types of Plate Boundaries
• Divergent Boundary
– move away from each other
• Convergent Boundary
– move toward each other
• Transform Boundary
– move past each other
Updated
Created by C. Ippolito
April 2009
Divergent Boundary
• plates move apart
– mantle convection
• Mid Atlantic Ridge
• East Pacific Rise
Updated
Created by C. Ippolito
April 2009
Convergent Boundary
• plates moving toward each other
– Subduction Boundary
• one plate moves under the other
– ocean-ocean
» deep sea trenches
» island arcs
– ocean-continent
» coastal volcanoes
– Collision Boundary
• plates push against each other form mtns
– continent-continent
» Himalays
Updated
Created by C. Ippolito
April 2009
Transform Boundary
• plates slide past each other
– earthquake activity
• San Andreas Fault
• North Anatolian Fault (Turkey)
Updated
Created by C. Ippolito
April 2009
Causes of Plate Movement
• Mantle Convection
– Magma hotter and less dense at ridge
– As it rises and moves away it pulls plate
• Ridge Push
– New formed rock cools/is more dense
– Gravity has it “slide” away from ridge
• Slab Pull
– At subduction zone denser plate “pulls
down”
Updated
Created by C. Ippolito
April 2009