Plate Tectonics

Rearranging Earth’s Surface

Tectonic ProcessesGOAL: To

understand the processes behind the distribution of Earth’s continents and oceans

Tectonic Processes

1. Alfred Wegener and how a scientific paradigm operates

2. Structure of Earth allows continents to move

3. Types of Plate Interactions

a. divergence b. convergence c. transform

4. Hot Spots

1. Alfred Wegener and how a scientific paradigm operates

"Scientists still do not appear to understand sufficiently that all earth sciences must contribute evidence toward unveiling the state of our planet in earlier times, and that the truth of the matter can only be reached by combing all this evidence. . . It is only by combing the information furnished by all the earth sciences that we can hope to determine 'truth' here, that is to say, to find the picture that sets out all the known facts in the best arrangement and that therefore has the highest degree of probability. Further, we have to be prepared always for the possibility that each new discovery, no matter what science furnishes it, may modify the conclusions we draw."Alfred Wegener. The Origins of Continents and Oceans (4th edition)

Field work: Atlantic once closed

Shape MatchRocks MatchFossils Match

Lifetime of work

Theory of Continental Drift

Meteorologist proposes

to change geology

1st edition 1915

Earlier, Sir Francis Bacon

wondered about similar shape of South America and Africa coastline (animation in Classroom Resources Folder)

Until 1960s –Utter Rejection by Geologists

Dr. Rollin T. Chamberlin of the University of Chicago said, "Wegener's hypothesis in general is of the footloose type, in that it takes considerable liberty with our globe, and is less bound by restrictions or tied down by awkward, ugly facts than most of its rival theories."

"Utter, damned rot!" W.B. Scott, President of the American Philosophical Society

American Association of Petroleum Geologists organized a symposium specifically in opposition to the continental drift hypothesis.

Today: We Map Tectonic Plates

Classroom Resources Folder

Today: We Accept that most Earthquakes and Volcanoes occur

along boundaries of Tectonic Plates

Today: We Accept Plate Movement

Today: We Accept Pangaeaand its breakup

Classroom Resources

Earth in the FutureAnimation of Drift Over Time

Pangaea Breakup

Online Video Presentations

Why the opposition & shift?• An example of how a discipline can get

“locked into” a pathway of mental thinking for decades (paradigm), rejecting the idea of moving continents.

• An example of how a discipline protects its “turf” – rejecting the thoughts of a meteorologist.

• Enough time for the opponents to die, and a bunch of new geologists in the 1960s to challenge “the establishment”.

• Reminder throughout this class that ideas shift and much depends on the mental framework of the scientist

2. Structure of Earth allows continents to moveWegener could not answer a

fundamental question of HOW continents could move.

But geology advanced to the point to begin to understand Earth’s internal structure & how it allows continental drift

Earth’s Structure

Brittle Crust Floats on Flowing Asthenosphere

Different Crusts: 5/6th submerged(isostatic balance)

Ocean Crust Continental Crust

Dense (sima) Lighter (sial)

Isostacy crust adjusts to

create a balance (equilibrium)

Classroom Resources

IsostacyMtnRoot.swf – animation showing that erosion of a mountain chain creates a condition whereby the root makes the mountain chain rise up to maintain isostatic equilibrium

Human Induced Change

2 continental plates under Tibet

To reach isostatic

balance, Tibet

Plateau

rises

Too thick, so get uplift

Effects Of Erosion on Isostacy

Earth oozes at different rates

Asthenosphere flows

Even the crust adjusts

Reason for Movement

Excess heat from radioactive decay creates liquid outer core (and magnetic field), and forces mantle to have convection

Exactly how

mantle moves?

ASU view

Classroom Resource

DowngoingSlab.swf – animation showing that a subducting plate might descend all the way through the mantle down to the core

Classroom Resources

Animation of a theoretical model showing sinking crust and rising hot plumes – all in the mantle

3. TYPES OF PLATE INTERACTION

Stream Systems on

Dynamic Earth

3. Type of Plate Interactionsa. Divergent Boundaries

Mid-ocean

ridges are

places of

plate divergence

Mid-Atlantic Ridge is the Icon

East

Pacific

Rise

Mid

Atlantic

Ridge

Mid Indian

Ridge

Why a ridge? Why not a Valley?

Heat makes the large structure rise up, but at the axis there is a rift valley from spreading

Sea Floor Spreading: Key to Rejecting the Old Ways

“Plate Tectonics” = continental drift + sea-floor spreading

Rename the theory with new evidence:

1. Potassium-Argon dating

2. Paleomagnetism

Potassium -> Argon Dating

Discovery: middle of ocean ridges youngest

Millions of years before present

Classroom Resources

Animation showing ages of ocean crust getting older away from spreading

Paleomagnetism

Classroom ResourcesVisualizing reversals of

magnetic field and how this creates a mirror image on the two sides of a spreading center

Lava has minerals that “record” the magnetic field

Paleomagnetism in Symmetry

Conclusion

was that

Sea floors

Spreading

apart

Current

“Brunhes”

orientation to

north has lasted

longer than most

(0.8 million).

Current

magnetic pole

moving fast,

Towards Siberia

at 25 mi/yr.

Don’t Worry!

Hollywood movie “The Core” – rediculous

It will take thousands of years to shift

Source for Latest Info:

Website

Continents can also spreadAtlantic Opened up Africa is Rifting

Classroom Resource

EastAfricaRifts.swf – animation showing rifting of East Africa/Red Sea through the process of plate divergence

Obvious question: with making new sea floor, why isn’t Earth expanding?

Old ocean plates undergo “subduction”

3. Type of Plate Interactionsb. Convergent Boundaries

Oceanic-Continental Convergence

Denser Oceanic Crust SubductsTrench Forms

Volcanoes FormLithosphere Subjects Into AsthenosphereEarthquakes Common All Along Boundary

Andes

Nazca plate collide with South American Plate

Cartoon

Latest Research from Nature

Classroom ResourcesVisualizations about the Andes Mtns as from

Convegence of Ocean & Continental Plates

Classroom Resources

Ocean_Cont_Converg.swf – animation showing that an ocean plate subducting under a continental plate explains the sea-floor trench, the mountain belt, earthquakes and volcanoes

From the East-Pacific Rise, the Pacific plate moves towards subduction in the Aleutian Trench

Ocean-Cont.

Convergence

in Pacific

Northwest

Island Arcs from Ocean-Ocean Convergence

Older colder ocean plate

subducts

Classroom ResourceOcean_Ocean_Converg.swf – animation showing

that a cold ocean plate subducting under a warm ocean plate explains the sea-floor trench, earthquakes and a chain of volcanoes called and Island Arc

Convergence of 2 continental platesExample of Himalaya

Classroom Resources

Animations of Himalaya Formation

From Hodges, ASU

Formation of Appalachian Mountains resulted from the collision of the African and European Plates with North American Plate prior to 300 million years ago.

Ural Mountains

Formation of the Ural Mountains related to collision tectonics prior to 300 Ma ago.

Convergence & Tsunami

Effects Of Plate Locking

EQ (or landslide or volcanic eruption ) Movement Generates the Wave that travels about 500 mph

Classroom ResourcesShows how Tsunami

can be made from subduction

Shows time sequence in Tsunami destroying coastal city in Alaksa

Classroom Resource

TsunamiGeneration.swf – animation showing that faulting along an ocean floor from compression can generate a Tsunami

Animated gif

Mega-Quake Set off 2004 Tsunami & will happen

again

Energy ripple

Sri Lanka Sumatra Uplift

Indonesia

Indonesia

Has Happened, Will Happen Again

Hilo, 1960

In Classroom Resources Folder, Animation of Chile EQ generating Tsunami that destroyed Hilo in 1960

3. Type of Plate Interactionsc. Transform Boundaries

Side-by-side motion

along San Andreas zone

Transform motion of the San Andreas Fault can be seen by offset of streams that cross the fault zone.

California Won’t Fall into the Ocean

Continent is 5/6ths submerged, so it is anchored very tight

Classroom ResourceAnimation showing how there used

to be convergence along the California coast, but it turned into a transform boundary

Animation of San Francisco Peninsula Topography shows the “gash” of the San Andreas fault zone

Other Transform Boundaries

4. Hot Spots

Often in the middle of a plate

Focus here on Hawaii & Yellowstone

Hawaiian Hotspot

Classroom Resources

Animation of Hawaii as moves over Hot Spot

Trail of the Hot Spot

Note change in direction 43 myr agoChange in direction 43 myr ago

Alternative Hypothesis

Yellowstone Hot Spot

Online VisualizationsTsunami Visualizationshttp://serc.carleton.edu/NAGTWorkshops/visualization/collections/tsunami.htmlPlate Tectonic Movement Visualizationshttp://serc.carleton.edu/NAGTWorkshops/visualization/PTMovements.htmlIsostacyhttp://serc.carleton.edu/NAGTWorkshops/visualization/collections/IsoGrav.htmlMountain Uplifthttp://serc.carleton.edu/NAGTWorkshops/visualization/collections/mouneros.htmlEarth History

http://serc.carleton.edu/NAGTWorkshops/visualization/collections/geotime.htmlMountain Buildinghttp://serc.carleton.edu/NAGTWorkshops/visualization/collections/orogeny.html

Imagery seen in this presentation is courtesy of Ron Dorn and other ASU colleagues, students and colleagues in other academic departments, individual illustrations in scholarly journals such as Science and Nature, scholarly societies such as the Association of American Geographers, city,state governments, other countries government websites and U.S. government agencies such as NASA, USGS, NRCS, Library of Congress, U.S. Fish and Wildlife Service USAID and NOAA.c