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Plate Boundaries
Review: Wegener's proposal
Wegener - continental drift hypothesis4 lines of evidence
• Continental puzzle • Fossil records• Matching mountain ranges• Ancient climate
Main objection toInability to provide a logical mechanism
Earth’s internal structureEarth’s internal layers can be defined by
• Chemical composition• Physical properties
Crust two types Continental Oceanic (denser)
• Mantle 82% of the volume of the Earth
• Core solid Iron & nickel
Density
Density is a physical property that ties most things on earth together?
Anything that works through convection currents• Plate movements• ocean currents• Weather
Earth’s internal structure
Four main layers of Earth based on its physical properties and mechanical strength are:
• Lithosphere• Asthenosphere• Mesosphere• Core
Earth’s internal structure
Lithosphere • Solid crust and small part of the mantle stuck to the crust
Asthenosphere • Hotter and more fluid than lithosphere• Allows for motion of lithosphere above
Plate Boundaries
3 Types of plate boundaries • Divergent plate boundaries
(constructive margins)
• Convergent plate boundaries (destructive margins)
• Transform fault plate boundaries
Plate boundaries
Divergent plate boundaries (constructive margins) • Two plates move apart as a result of the mantle
material upwelling from convection.
Key Features: Oceanic Ridges - develop along well-developed boundaries or ridges, the seafloor spreads apart and creates new crust.
Rift Valleys – found on land where continent is being ripped apart.
Examples
Iceland
The East African rift
Divergent boundaries
Figure 15.10
They are located most on mid-oceanic ridges
Rift Valleys
Oceanic-continental convergent plate boundary
• Denser oceanic slab sinks into the asthenosphere
• Pockets of magma develop and rise as a result of carbon and water pulled down with the subducting plate.
. Key Features:Continental Volcanic Arcs or (Volcanic mountain ranges) Examples: Andes & CascadesOcean Trench: form as lithosphere is subducted into the mantle.
Oceanic-oceanic convergent plate boundary
• Two oceanic slabs converge and one descends beneath
• Key Features: • Volcanic Island Arcs: form
as volcanoes emerge from the sea floor from subduction.
• Example: Japan and Alaskan Island Chain (NOT Hawaii!)
• Deep Ocean trenches • Example: marians trench
Continental-continental convergent plate boundary
Figure 15.14 C
Two continents collide both made of lower density rocks and neither wants to subduct as a result the material lifts up into very high mountain ranges.
Key Feature: Very tall non-volcanic mountain ranges
Example: Himalayas
The collision of India and Asia produced the Himalayas
Figure 15.15 A
Before
After
Transform fault boundariesPlates slide past each
other, no new crust is created or destroyed.
Most are found perpendicular to mid-ocean ridges as they Aid in the movement of divergent boundaries.
Most Famous Example:
San Andreas Fault