Download Plate Tectonics - Department of Physics and Astronomy

Plate Tectonics
5 November 2015
Chapter 17
Great Idea:
The entire Earth is still changing, due to the slow
convection of soft, hot rocks deep within the planet.
1
Chapter Outline
• The Dynamic Earth
• Plate Tectonics: A Unifying View of
Earth
• Another Look at Volcanoes and
Earthquakes
2
The Dynamic Earth
3
The Dynamic Earth
• Small-scale changes
– Construction site
• Erosion by rain
• Large-scale changes
– Volcanoes
– Earthquakes
– Erosion
4
The Case of the
Disappearing Mountains
• Erosion
– Few hundred million years
– Mountains continually forming
• Earth’s surface is not static
5
Volcanoes and EarthquakesEvidence of Earth’s Inner Forces
• Volcano
– Magma breaks
through surface
• Earthquake
– Rocks breaks
along fault
– Energy
transmitted as
wave
– Richter scale
6
The Movement of the Continents
• F. Bacon
– Continents like a
puzzle
• Wegener
– Continental Drift
• Continents in
motion
• Current Evidence
– Ocean Floors
– Magnetic
Reversals
– Rock Ages
7
Ocean Floors
• Mapping
– Ocean floor dynamic
• Canyons, mountains
• Mid-Atlantic Ridge
– Earthquakes,
volcanoes,
lava flows
8
Magnetic Reversals
• Earth’s magnetic field
– Changes periodically
• Magnetite
– Crystals in lava align to magnetic field
• Paleomagnetism
• Seafloor Spreading
– New rock comes to surface
9
Magnetic Reversals
10
Rock Ages
• Radioactive Isotopes
– Rocks near Mid-Atlantic Ridge younger
– Rocks farther away older
11
New Support for the Theory
• Measuring motion of continents
• Radio Astronomy
– Measured arrival of radio waves
– Repeated over several years
• North America and Europe
– Separating at 5 cm per year
12
Plate Tectonics: A Unifying
View of Earth
13
Plate Tectonics
• Plate Tectonics
– Large-scale surface
features
– Related phenomena
• Tectonic plates
– Rigid, moving sheet of
rock
– Crust and upper mantle
– Continental
• 100 km thick
• Lower density (granite)
– Oceanic
• 8-10 km thick
• Dense rock (basalt)
• Earth’s surface
– ¼ continent, ¾ water
14
Earth’s Plates
15
The Convecting Mantle
• Mantle convection
– Motion driven by Earth’s interior heat energy
• Sources of energy
– Gravitational potential energy
– Decay of radioactive elements
• Movement
– Heat moves to cooler regions
– Convection cells in mantle
– Very slow
• 200 million years for one cycle
16
Plate Boundaries
• Three Main Boundary Types
– Divergent
– Convergent
– Transform
17
Divergent Boundaries
• Characteristics
– Volcanoes
• Chain of mountains
– Earthquakes
• Seafloor spreading
– Plates pushed apart
– Old spreading centers
• Located in middle of ocean
– New spreading centers
• May begin anywhere
18
Convergent Plate Boundaries
• Types
– Oceanic-oceanic
• Subduction zone
– Deep oceanic trench
– Island arc
– Continental-continental
• High, jagged mountain chain
– Continental-oceanic
• Subduction zone
– Deep oceanic trench
– Coastal mountain range
19
Transform Plate Boundary
• Two plates move past each other
– NOT smooth
– Earthquakes as a result of movement
20
The Geological History of
North America
• Northeastern Canada and Greenland
– Several billion years old
• Western US
– Terranes
• Added to continent over time
• Appalachian Mountains
– Formed 450-300 million years ago
– Continental-continental convergence zone
• Rocky Mountains
– 60 million years ago
– Warping, folding and fracturing of continent
• The Colorado Plateau
– Gentle uplift
• The Sierra Nevada
– Molten rock pushed up sediments
21
Another Look at Volcanoes
and Earthquakes
• Plates and Volcanism
– Divergent Plate
Boundaries
– Convergent Plate
Boundaries
• Subduction zones
– Hotspots
• Source stationary,
plates move
• Chain of volcanoes
• Earthquakes
– At plate boundaries
or elsewhere
22
Seismology: Exploring Earth’s
Interior with Earthquakes
• Seismology
– Study of sound vibrations within earth
– Used to determine earth’s inner structure
• Seismic waves
– Compressional or longitudinal
• P-waves (pressure waves)
– Transverse or shear waves
• S-waves
23
Seismology: Exploring Earth’s
Interior with Earthquakes
24
• Plate tectonics is
involved in the
formation of the
three major
categories of
rocks
– Igneous Rock
• cooled from
molten material
– Sedimentary Rock
• Layered eroded
material formed
by the action of
wind, water, or
ice
– Metamorphic Rock
• Rock that has
been altered in
the solid state
by extreme heat
and pressure
25