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Review Plate boundaries Divergent Oceanic and continental Convergent Oceanic-continental Continental volcanic arcs Oceanic-oceanic Volcanic island arcs Continental-continental Mountain ranges - Himalayas Transform Aid in crustal movement
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Theory of Plate Tectonics
Lecture 4
ReviewWegener - continental drift hypothesis
Continental puzzle Fossil recordsMatching mountain rangesAncient climate
Main objection to Wegener's proposal Inability to provide a mechanism
Theory of Plate tectonics4 scientific developments
• Ruggedness and youth of ocean floor• Earthquakes and volcanoes active along ocean mountain
ranges and trenches• Repeated changes of earth’s magnetic field• Spreading of the ocean floor hypothesis
Review
Plate boundariesDivergent
• Oceanic and continentalConvergent
• Oceanic-continental Continental volcanic arcs
• Oceanic-oceanic Volcanic island arcs
• Continental-continental Mountain ranges - Himalayas
Transform • Aid in crustal movement
Theory of Plate Tectonics-Paleomagnetism
Paleomagnetism is probably the most persuasive evidence supporting the theory of plate tectonics
Theory of Plate tectonics -Evidence from ocean drilling
Seafloor spreadingSome of the most convincing evidence
confirming seafloor spreading Evidence from drilling directly into ocean-floor sediment
Age of deepest sediments - furthest away from boundary
Theory of Plate Tectonics - Hot spots and mantle plumes
Hot spots - caused by rising plumes of mantle material
Volcanoes - Hawaiian islands over hot spot
The further from Hawaii the older the island
Pacific plate moves over hot spot - volcanic mountains form
Evidence plates moved
What drives plate motion
Driving mechanism of plate tectonics • Several mechanisms contribute to plate
motion• Scientists generally agree that convection
occurring in the mantle is the basic driving force
• Warm less dense material rises• Cooler, denser material sinks• Movement of the plates and mantle is driven by the
unequal distribution of Earth’s heat• Heat is generated by radioactive decay of elements such
as Uranium found in the mantle and crust
Several models to explain plate movement have been proposed
Figure 15.26
• Model 1 - Slab-pull and slab-push model • Descending oceanic crust pulls the plate -
downward arm of convective flow• Elevated ridge system pushes the plate
Several models to explain plate movement have been proposed
• Model 2 - Plate-mantle convection • Mantle plumes extend from mantle-core
boundary and cause convection within the mantle
• 2 different models for plate-mantle convection
• see the following figures
Whole-mantle convectionCold oceanic crust descends into the mantleHot mantle plumes transport heat toward the surface
Deep-layer modelEarth’s heat causes these layers of convection to slowly swell and shrink in complex patternsSome material from the lower layer flows upward as mantle plumes
Plate movementWe still have a lot to learnWe do know this:
The unequal distribution of heat within the Earth causes the thermal convection in the mantle that ultimately drives plate motion
Measuring plate motion
Figure 15.25
Using space-age technology to directly measure the relative motion of plates Very Long Baseline Interferometry (VLBI)
large numbers of time difference measurements from distant sources observed with a global network of antennas over a period of time
Global Positioning System (GPS)
A possible view of the world 50 million years from now
Figure 15.28
• Areas west of the San Andreas Fault slide northward past the North American plate
• Africa collides with Eurasia, closing the Mediterranean and initiating mountain building
• Australia and new Guinea are on a collision course with Asia