Chapter 4: Plate Tectonics K2 in the Himalaya, inset round submersible (beneath the submarine) that went to the Marianas Trench in 1960
http://www.nydailynews.com/news/world/james-cameron-presents-record-setting-deep-sea-expedition-article-1.1215139
Learning Objectives A revolution in geology Describe the processes of continental drift and seafloor spreading. The plate tectonic model Outline the theory of plate tectonics, including the role of mantle convection.
A Revolution in Geology Wegner s Hypothesis of Continental Drift Continental drift: Slow, lateral movement of continents along Earth s surface Pangaea Supercontinent that split into fragments that later became our present continents Existed about 320 million years ago http://www.nature.nps.gov/geology/usgsnps/animate/a08.gif Figure 4.1
A Revolution in Geology Matching Geology Matching rocks: How well do the continents fit?
A Revolution in Geology Matching Geology Matching rocks: How well do the ages match?
A Revolution in Geology Matching fossils What evidence did the fossils leave? Glossopteris: ancient tree with large seeds found on several continents Mesosaurus: small reptile found in Brazil and S. Africa Matching Geology Figure 4.3d Glossopteris
A Revolution in Geology Matching Geology Figure 4.3e Areas where Glossopteris fossils have been found
A Revolution in Geology Matching Geology Evidence left by glaciers What evidence did the glaciers leave?
A Revolution in Geology Apparent Polar Wandering Paths Paleomagnetism: tool for studying Earth s history Apparent polar wandering Magnetic poles wandered Used to indicate America and Europe were a single continent
There are minerals within rocks that have magnetic properties. http://skywalker.cochise.edu/wellerr/mineral/magnetite/magnetitel.htm http://www.wrpsteacher.org/craigontl/cns%20chemistry%20biology/continentaldriftglacialevidence.html
A Revolution in Geology The Puzzle-Piece Argument Where is the true edge of the continent? Figure 4.2
A Revolution in Geology Sea floor spreading? Figure 4.6 Age of ocean floor
A Revolution in Geology The Missing Clue: Seafloor Spreading Seafloor spreading The process by which the seafloor splits and moves apart along a midocean ridge. New oceanic crust forms along the ridge. Decisive piece of evidence for seafloor spreading: Ages of seafloor rocks increase with distance from the ridge. http://www.mysciencebox.org/seafloor
Figure 4.7 Seafloor spreading
A Revolution in Geology The Missing Clue: Seafloor Spreading Global Positioning Systems (GPS) Valuable tool Used to track the plate motions as the ground moves Figure 4.8 Measuring plate motions with GPS
The Plate Tectonic Model Plate tectonics: The movement and interactions of large fragments of Earth s lithosphere (i.e., plates) Figure 4.9 Earthquake epicenter locations
The Plate Tectonic Model Plate Tectonics in a Nutshell Lithosphere: Rocky outer layer is thin. Asthenosphere: Below lithosphere; layer is weak due to hot temperature (near melting point). Relationship between lithosphere and asthenosphere is isostasy (lithosphere is essentially floating on the asthenosphere). Plate: Large fragment of rigid lithosphere bounded on all sides by faults Fault: A fracture in Earth s crust along which movement has occurred
The Plate Tectonic Model Plate Tectonics in a Nutshell Figure 4.10 Tectonic plates
The Plate Tectonic Model Types of Plate Margins Plates can diverge or converge, or they can slide past each other horizontally. Earthquake: Release of energy that has been stored; occurs along faults. Focus: Point where the earthquake begins (within the crust) Epicenter: Point on the Earth s surface directly above the focus
The Plate Tectonic Model Divergent margins A boundary along which two plates move apart from one another Types of Plate Margins http://academic.evergreen.edu/g/grossmaz/hammvm/index.html
The Plate Tectonic Model Convergent margin A boundary along which two plates come together Types of Plate Margins
The Plate Tectonic Model Subduction zone Types of Plate Margins A boundary along which one lithosphere plate plunges into the mantle beneath another plate Deep oceanic trenches Arcs of volcanoes (either on ocean floor as islands, or on land as a volcanic mountain chain) http://www.meted.ucar.edu/westpac/overview/print.htm
The Plate Tectonic Model Continental collision margin A boundary along which two lithosphere plates with continents embedded in them collide High mountain ranges Types of Plate Margins Thickened crust behind the mountain range http://zebu.uoregon.edu/1996/ph123/converge.html
The Plate Tectonic Model Types of Plate Margins Figure 4.11c Continental collision zone
The Plate Tectonic Model Transform fault margin A fracture in the lithosphere where two plates slide past each other Types of Plate Margins Figure 4.11d San Andreas fault, California http://pubs.usgs.gov/gip/earthq3/along2.html
Types of plate margins Figure 4.12 Plate Margins: A summary
The Plate Tectonic Model Search for a Mechanism for Plate Motion Earth s internal heat: Conduction Slow release of heat Convection A form of heat transfer in which hot material circulates from hotter to colder regions, looses its heat, and then repeats the cycle Figure 4.13a
Figure 4.13b Convection in the mantle
Tectonic cycle The Plate Tectonic Model The Tectonic Cycle: Past, Present, Future Movements/ interactions by which rocks are cycled from the mantle to the crust and back Includes earthquakes, volcanism, and plate motion, driven by convection in the mantle As a result, seafloor recycles itself every 200 million years The Wilson Cycle http://csmres.jmu.edu/geollab/fichter/wilson/wilsonsimp.html
The tectonic cycle Figure 4.14 The tectonic cycle
The tectonic cycle Figure 4.15 Before Pangaea
Earth of the future
Amazing Places: Hawaiian Islands Hot spot example: Hawaiian Islands http://library.thinkquest.org/5410/island_formation_web_page/ht ml_folder/formation11.html
What about Yellowstone? http://volcano.oregonstate.edu/v wdocs/volc_images/north_ameri ca/yellowstone.html http://fi.freewalls.org/wallpaper/gardner-yellowstone-national-park-montana1/
Critical Thinking What are some of the important questions about plate tectonics that remain unanswered today? Why do geologists call plate tectonics a unifying theory? As Africa slowly separated from Arabia, and the sea began to enter the rift, what kind of sediment would you expect to be deposited?