Download Plate Tectonics Continental Drift

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Plate Tectonics
In 1912, Alfred Lothar Wegener (1880-1930), a German meteorologist,
published the hypothesis of continental drift with multiple lines of
evidence to back it up. Wegener proposed that all of the continents were
once joined together as one supercontinent that he called Pangea.
• Introduction
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Continental Drift
Predecessor of plate tectonics: Continental drift hypothesis
What is the theory of plate tectonics?
What is a plate?
How do we find their edges?
How many plates are there?
Why is plate tectonics important?
• Types of relative plate movements (and related stresses)
• Types of plate boundaries
• Plate boundaries and earthquake depths
• Measuring plate motions
• Why do plates move?
News, articles, etc. on Plate Tectonics
https://www.diigo.com/outliner/6vks13/Plate-Tectonics?key=hrh02jmyit
This Dynamic Earth - USGS
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Fossil evidence for once
joined continents
Later studies have allowed the positions of the continents at different
times in Earth history to be determined, and have documented the
breakup of Pangea. http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?PlateMoTime
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This Dynamic Earth - USGS
Related puzzle activity: http://volcanoes.usgs.gov/about/edu/dynamicplanet/wegener/
Plate Tectonics
This Dynamic Earth - USGS
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Today, we know that it isn’t just the continents that have moved. Rather, the
Earth’s surface is broken into pieces of continental and/or ocean crust called
plates. Plate tectonics deals with the nature of these plates, what happens at their
boundaries, how and why they move, etc.
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Plate tectonics also
explains the locations of
earthquake faults,
volcanoes, and major
mountain ranges.
Photos from: This Dynamic Earth
(USGS) and Understanding Earth
Fig 20.3 - Understanding Earth
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Patterns in the locations of earthquakes and volcanoes
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Active continental margins (plate boundary)
vs.
Passive continental margins (no plate boundary)
The discovery of extensive ocean ridges and young ages for the ocean
floor (in the 1940s and 1950s) provided another important clue.
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The western margin of North America is an active area with earthquakes (yellow) and volcanic
activity (red). In contrast, the eastern margin of North America is a quiet passive area with no
active volcanoes and few earthquakes. We now know that the active zones coincide with the
boundaries between plates (blue).
USGS
Pioneering woman who mapped the ocean floor
https://www.theguardian.com/science/2016/mar/13/terrawatch-kate-ravilious-marie-tharp-mid-atlantic-ridge?CMP=twt_a-science_b-gdnscience
Marie Tharp, Pioneering Mapmaker of the Ocean Floor
http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?PlateBound
http://www.ldeo.columbia.edu/news-events/remembered-marie-tharp-pioneering-mapmaker-ocean-floor
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Sea floor magnetism was a
key part of mapping ocean
floor age and figuring out the
processes responsible for the
pattern
Zones of progressively deeper earthquakes revealed the existence of 10
subduction. This led to an understanding of how ocean crust is recycled
at ocean trenches.
Geology 2nd ed. Chernicoff
This Dynamic Earth - USGS
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What is a plate? – The brittle outer part of the earth (crust and uppermost
mantle) is called the lithosphere. The lithosphere is broken into plates that move on
the asthenosphere, a part of the mantle which is plastic (able to flow).
Types of relative plate movements and boundaries
and related stresses and fault types
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Compression
Extension
Reverse and
thrust faults
Normal faults
Folding
Stretching and
thinning
Shear
Strike-slip faults
This Dynamic Earth - USGS
Shearing
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The mid-ocean ridge (shown in red) winds its way between the
continents much like the seam on a baseball This Dynamic Earth - USGS
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This Dynamic Earth - USGS
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Fig 1.15 - Understanding Earth
This Dynamic Earth - USGS
Mid-Atlantic
Ridge at Iceland
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Continental Rifting
East African Rift
This Dynamic Earth - USGS
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http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?DivergBound
Fig 20.3 - Understanding Earth
Africa
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Geology 2nd ed. - Chernicoff (originally from Bullard,
1969, The Origin of the Continents: Scientific American)
East African Rift
SOUTH
Gulf of Aden
Red Sea
Continental rifting:
The Afar Triangle
Photo from Space Shuttle:
STS061-079-024 - NASA
Next: 20-Plate Divergence.mov
(Red Sea rift)
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Transform Boundaries
http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?TranFault
Transform plate boundary
San Andreas fault, California
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Fig 1.17 - Understanding Earth
This Dynamic Earth - USGS
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Ocean-ocean convergent boundary
This Dynamic Earth - USGS
Japan, an example of an
oceanic island arc
Photo from Space Shuttle:
STS059-218-044 - NASA
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Ocean-continent convergent boundary
This Dynamic Earth - USGS
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Intrusive igneous rocks formed along an ancient volcanic arc: Part of the
Sierra-Nevada batholith in Yosemite National Park
http://www.npr.org/templates/story/story.php?storyId=124361777
(Charles Darwin witnessed 1895 Chilean quake, deduced that the Andes required millions of years to build)
Next: 20-Ocean-Continent.mov (Andean subduction zone)
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Continent-continent convergent boundary
This Dynamic Earth - USGS
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Formation of the highest
mountains on earth by
continent-continent
collision
This Dynamic Earth - USGS
Next: 20-Continent-Continent.mov
(India-Asia collision zone)
PT Summary:
http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?MotionatPlate12
http://terra.rice.edu/plateboundary .
ap based on widely available dataset ETOPO5
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Plate boundaries and earthquake depths
All types of plate boundaries can produce shallow earthquakes.
The deepest earthquakes (and some of the largest earthquakes) occur in
subduction zones.
Fig. 10-16 Chernicoff - Geology
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Measuring plate motions - using hot spots
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Hotspots and plate movements
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dia.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?HotSpot12
Map of part of the Pacific ocean floor showing the 6,000-km-long Hawaiian
Ridge-Emperor Seamounts chain – This volcanic trail of the Hawaiian
This Dynamic Earth - USGS
hotspot could be related to a mantle plume
Geology 2nd ed.
- Chernicoff
Hot spots and the opening of the south Atlantic Ocean
http://www.see.leeds.ac.uk/structure/dynamicearth/plates_move/hotspots/index.htm
http://www.see.leeds.ac.uk/structure/dynamicearth/plates_move/index.htm
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Measuring plate motions - using sea floor age
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How do we know plates move today? From Earthquakes, GPS, VLBI, & SLR
How we know: http://www.see.leeds.ac.uk/structure/dynamicearth/plates_move/index.htm 32
NASA GPS Time Series plate movements: http://sideshow.jpl.nasa.gov/post/series.html
GPS time series: http://en.wikipedia.org/wiki/File:Global_plate_motion_2008-04-17.jpg
More GPS http://www.dpc.ucar.edu/VoyagerJr/gpsplatebound.html
Fig 20.11 - Understanding Earth
A GPS ground receiver at Augustine Volcano (Cook Inlet, Alaska) recording signals
sent by GPS satellites. Artist's conception of a Global Positioning System satellite in
orbit shown in inset. Source: USGS
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Major plate boundaries and their rates of movement
Projected future positions of the continents - 100 million years from now: If
current plate movements continue unchanged, part of California will become an
island off the coast of Washington, the Mediterranean Sea may close, and eastern
Africa may become an island. Geology 2nd ed. - Chernicoff
Fig 20.12 - Understanding Earth
Since 1994, Australia has moved about 5 feet! http://newatlas.com/australia-gda2020/44674/
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Plate Tectonics:
Why do plates move?
The general scientific consensus is
that plate movements are related
to convection.
Best fit to evidence for
major force causing
plate movements
Convection in the Earth results
from the escape of heat from the
interior and involves the pull of
gravity on rocks of different
densities.
Essentially, colder, more dense
rocks sink while hotter, less dense
rocks rise.
Suggested mechanisms
to drive plate motions
Partly true, but convection
not as organized as this
Fig 1.13 - Understanding Earth
Fig 20.25 - Understanding Earth
Doesn’t
match rates
of movement
Deep plumes exist,
but are not a major
cause of plate
movements
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Not only do subducting plates sink, the boundary can also “roll back”
over time. This causes the subduction zone to pull on both plates.
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Image source: http://www.gly.uga.edu/railsback/DynamicPlateTectonics.html
ridge
mid-ocean
position of
Compression of continent because of subduction
travels with west-moving plate.
of sketches.
ck of trench
the sequence
Rollback
New sea
floor made
throughout
Rollback
y
Rollback
Subduction
with
rollback pulls on
plates
Image source: http://www.gly.uga.edu/railsback/DynamicPlateTectonics.html
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Plate boundary locations change over time
New sea floor
made at
spreading ridge
ossible modes
of behavior
of oceanic
lithosphere
t convergent
ate boundaries
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I n it ia l p o s it io n
o f tre n c h
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http://media.pearsoncmg.com/bc/bc_0media_geo/active_art/hdew_2e.html?ConvecTect
Image source: This Dynamic Earth – USGS http://pubs.usgs.gov/publications/text/dynamic.html
Subduction via
trennchward
motion and
rollback
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Time C
- cold, relatively dense lithosphere is pulled downward at subduction
zones and pulls the rest of the plate along behind it
Note
need
asthe
sprea
acco
beyo
Slab pull – probably the most important driver of plate movements
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Subduction of an
ocean ridge led to
formation of the San
Andreas fault
This Dynamic Earth - USGS
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This Dynamic Earth - U.S. Geological Survey
http://pubs.usgs.gov/publications/text/dynamic.html
Subduction of
an ocean ridge
led to
formation of
the San
Andreas fault
Paleomap Project - Continent locations of the past, present and future.
http://www.scotese.com/
Plate Tectonics - U.S.G.S. Cascades Volcano Observatory
http://vulcan.wr.usgs.gov/Glossary/PlateTectonics/framework.html
What is Plate Tectonics? – USGS and National Park Service
http://www2.nature.nps.gov/geology/usgsnps/pltec/pltec1.html
Plate Tectonics Animations – USGS and National Park Service
This Dynamic Earth - USGS
http://www2.nature.nps.gov/geology/usgsnps/animate/pltecan.html
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Plate Tectonics
http://www.ucl.ac.uk/EarthSci/people/lidunka/GEOL2014/Geophysics1-%20Plate%20tectonics/PLATE%20TECTONICS.htm
How we know plates move – GPS, VLBI, etc.
http://www.see.leeds.ac.uk/structure/dynamicearth/plates_move/index.htm
NASA Space Geodesy Project – What is VLBI?
http://space-geodesy.nasa.gov/techniques/VLBI.html
Digital Tectonic Activity Map (combines topography, plate boundaries, movements, etc.)
http://denali.gsfc.nasa.gov/dtam/
Wegener's Puzzling Evidence Exercise (6th Grade Activity)
http://volcanoes.usgs.gov/about/edu/dynamicplanet/wegener/
CT scan of Earth links deep mantle plumes with volcanic hotspots
http://www.sciencedaily.com/releases/2015/09/150902134939.htm
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