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