1. Plate Tectonics Through Time
- The Shape of Today’s Sea
- Plate Tectonics and Ancient Oceans
Reading:
4th Ed. Ch 3 Sec 31, Ch 4 Secs 6, 8-9, 11, 18-19
5th Ed. Ch 3 Sec 31, Ch 4 Secs 6-9, 11, 17-18
Graphic: CNN, Jan 23, 2003. Photo by the Associated Press.
2. Review - How Does Plate Tectonics Work?
Plates move relative to one another
Lithosphere is formed where plates pull apart
Lithosphere is destroyed where plates come together at subduction zones
Graphic: Garrison, 4th Ed., Fig. 3.13, pg 71.
3. Divergent and Convergent Plate Boundaries
Divergent –birthplaces of new oceans, locations of mid-ocean ridges
Convergent – plates come together, mountain building
4. The Shape of Today’s Sea
Graphic: See Garrison, 4th Ed., Fig. 4.30, pg 116, 5th Ed., Fig. 4.31, pg 108.
5. Continental Margins
Shelf - submerged edge of continent
Slope - transition between continental and oceanic crust
Rise - area at the base of the continental shelf covered by sediment deposited
from the shelf
Graphics: (left) California, as viewed from space, image courtesy of the SeaWiFS
Project, NASA/Goddard Space Flight Center and ORBIMAGE, (right)
Computer-generated visualization of the continental shelf, slope and rise off
the coast of Los Angeles, courtesy of the USGS Pacific Sea-Floor Mapping
Project.
6. Passive Margins
- far from plate boundaries
- common around the Atlantic Ocean
- broad continental shelves
- little tectonic activity
Graphic: Garrison, 4th Ed. Fig. 4.9, pg 101, 5th Ed. Fig. 4.8, pg 93.
7. Active Margins
- Coincide with plate boundaries
- Common around the Pacific Ocean
- Narrow continental shelves
- Significant tectonic activity
Graphic: See Garrison, 4th Ed. Fig. 4.9, pg 101, 5th Ed., Fig. 4.10, pg 94.
8. Deep Ocean Trenches
Are 3-6 km deeper than surrounding ocean
Tectonically active
Graphics:(top) Garrison, 4th Ed. Fig. 4.29, pg 115, 5th Ed. Fig. 4.30 pg 107,
(bottom) Garrison, 4th Ed. Fig. 4.28, pg 114, 5th Ed. Fig. 4.29, pg 107.
9. Volcanoes, Earthquakes and the Ring of Fire
“Ring of Fire” - a zone of intense volcanic activity around the Pacific basin
Most “Ring of Fire” volcanoes are formed as a result of processes at plate
boundaries
Graphics: (top) Locations of active volcanoes, from worldatlas.com, (bottom)
Earthquakes around the Pacific basin, courtesy USGS.
10. Plates on the Move
Lithospheric plates move 2-15 cm/yr
Over long times, these motions significantly rearrange continents and oceans
Graphic: Garrison 4th Ed., Fig. 3.14, pg 72, 5th Ed., Fig. 3.15, pg 68.
11. How Do You Grow a Continent?
As plates move, continents grow by accretion of microcontinents, island arcs and
old oceanic plateaus
These smaller pieces of continental material are not subducted because they are
not sufficiently dense
Graphic: Garrison, 4th Ed. Fig. 3.32, pg 85, 5th Ed. Fig. 3.34, pg 82.
12. The Wilson Cycle
Earth's crust is rearranged and recycled as plates move:
- Rifting of continents
- Seafloor spreading forms new ocean basins
- Subduction of old seafloor
- Building of continental platforms via accretion
- Suturing of continents to form mountain ranges
Graphic: Garrison, 4th Ed. Fig. 3.33, pg 86, 5th Ed. Fig. 3.36, pg 83.
13. Plate Motion Through Time
Modern geography can be traced back millions of years using
- fossil plants and animals
- rock assemblages
- magnetic properties of oceanic and continental rocks
Changes in climate occurred in conjunction with reorganizations of land and
ocean
Graphic: Garrison, 4th Ed. Fig. 3.18, pg 75, 5th Ed. Fig. 3.19, pg 71.
14. Plate Tectonics and Climate
Some influences on climate:
- Amount of land at various latitudes (poles vs equator vs midlatitudes)
- Circulation of the ocean
- Numbers and locations of mountain ranges
- Dust in the atmosphere from volcanic activity
Graphic: Garrison, 4th Ed. Fig. 3.18, pg 75, 5th Ed. Fig. 3.19, pg 71.
15. 356 Ma - Converging Continents
Shallow inland seas covered much of what is now North America
About 300-350 million years ago, ancient continents moved together to form a
vast supercontinent, Pangea
Graphic: Courtesy of C.Scotese, see
http://www.scotese.com/newpage4.htm
16. 237 Ma - A Supercontinent and a Great Ocean
Shallow seas and reefs set the stage for massive oil fields in the Middle East
Graphic: Courtesy of C.Scotese, see
http://www.scotese.com/newpage8.htm
17. 94 Ma -Formation of New Oceans
Breakup of southern continents gradually isolates Australia and Antarctica
As Pangea broke up, rifting opened the North and South Atlantic Oceans
Graphic: Courtesy of C.Scotese, see
http://www.scotese.com/cretaceo.htm
18. 50 Ma - A Widening Atlantic Ocean
Seafloor spreading continues to broaden the Atlantic Ocean
Northward motion of India sets the stage for lifting the Himalayas
Graphic: Courtesy of C.Scotese, see
http://www.scotese.com/newpage9.htm
19. 14 Ma - Connecting North and South America
Closing of the Isthmus of Panama dramatically affected ocean circulation
Graphic: Courtesy of C.Scotese, see http://www.scotese.com/miocene.htm
20. Plate Tectonics and Today's Ocean Basins
Pacific - bordered by many subduction zones
Atlantic and Indian - continue to broaden due to seafloor spreading
Graphic: Graphic: Courtesy of C.Scotese, see
http://www.scotese.com/modern.htm
21. Plate Tectonics and the Future?
Mediterranean closes, further lifing the Alps
If current trends continue, Hawaii will reach the Japan Trench in about 63
million years
Graphic: One assessment of the Earth 50 million years into the future. Courtesy
of C.Scotese, see http://www.scotese.com/future.htm
22. Preview of Next Lecture
Seawater and the Salt in the Sea (Why is the Sea Salty?)
Reading: 4th or 5th Ed. - Ch 6 Sec 2, Ch 7 Secs 2-6
Graphic: Deploying a Conductivity-Temperature-Depth (CTD) rosette, with water
sampling bottles to measure the physical and chemical properties of seawater.
Capt. R. A. Pawlowski, photographer. Image courtesy of NOAA.