Chapter 3 Plate Tectonics

Theory & Evolution

Assignment 1 – Summary of Why?

• Class results: 35 enrolled students

• 22 Seniors

• 33 Non Science majors• 7 Fear/Hate math• Interests (80% - say need Q GE) to finish or other• Alt. E w/ Algae• Most “Love the Oceans/Water” want to learn more

OUTLINE

• A Theory of Earth

• Historical Development of Plate Tectonics

• Earth’s layers

• Study of Plate Motions

• Summary of Plate Driving Forces

A Theory of Earth

• What is the Theory of Plate Tectonics?– Earth crust divided into plates, move independently

• In response to? – HEAT FLOW thru crust

What is continental drift?

The coming together or drifting apart of Continents on the face of earth

OUTLINE

• A Theory of Earth

• Historical Development of Plate Tectonics

• Earth’s layers

• Study of Plate Motions

• Summary of Plate Driving Forces

~1900

MOST Scientists considered Earth to be rigid, Stagnant . . .

Wegener’s idea hinted that:Crust (continents) floated in molten fluid

• Idea: – Earth’s rigid crust underlain by weak plastic interior. . .

RECALL

((HOT))

5500*C

6600*C

(HOT-molten fluid)

Mantle convection - serves as driving mechanism for continental drift

• What is Mantle convection?– Materials rising from mantle – spread out sideways (laterally)

and pulls continents w/ it.

Using Wegener’s idea – Arthur Holmes (1928) proposes:

MANTLE

Continents move

crustHot air/liquid rises. . .

Think of Boiling Pasta

1960s New Technolgies

• Sonar of ocean shows:– Mid ocean ridges (mtn ranges)

Warmcool

cool Warm

Warm

Warm

cool

coolcool

cool

cool

Heat flow=Greater at Mtn. Ridges

At odds w/ ideaOf Static earth. . ..

With Pangea/Mantle Convection idea Seafloor Spreading concept emerges. . .

Dietz/Hess (1960s)

What is the idea of Seafloor Spreading?

Earth’s crusts being driven apart (laterally) by convection currents. . .Submersibles confirm

lateralmovement

Mid ocean ridge

Plate Tectonics/ Seafloor Spreading

Submersibles confirm

lateralmovement

http://www.youtube.com/watch?v=AlHJqA8YkoI

Awesome Biological discoveries – mid ocean Ridges (hydrothermal vents)

http://www.youtube.com/watch?v=XotF9fzo4Vo&NR=11970s

2003

Seafloor SpreadingDirect evidence was lacking., . .

Paleomagnetism (study of magnetic properties in rocks)

(Iron)

RECALL+

-

-

Over (geologic time-100 Mya)Poles reverse (Polar Reversal)

+

-

+

+

-

-

How does this help confirm the theory of continental drift?

Curie Point – at certain temp. magnetic properties (elements) of rock solidifyAlign with earth’s current magnetic field. . .

Can determine Position of the “Poles” when the Rock formed. . .

Very Old

OldOlder

NewNewestVine-Matthews-Morley

HypothesisUsing Magnetometer

Discovered “Zebra stripes”Indicating polar reversals in seafloor and age distancesFrom mid Ocean Ridge

Where is the seafloor oldest & youngest above?

Mid ocean Ridge (Mtn)

Plate Tectonics confirmed-What’s really going on. .

Mid ocean ridge

SeaFloor spreading -makes new ocean crust (basalt)

Subduction- removes ocean crust. . zone

.(melts forms coast Mtns)

•Earth’s layers

shifting “Lithospheric plates”That move atop “plastic”. . .Asthenosphere

Lithosphere:Oceanic Crust vs Continental Crust• What is their composition?• Which is more dense/why?

Basalt(more dense~ 3 g cm-3) Lots of minerals/Iron, nickel etc

Granite/quartz(less dense~ 2.7 g cm-3)Mostly Silica/less minerals

Mid ocean ridge

OUTLINE

• A Theory of Earth

• Historical Development of Plate Tectonics

• Earth’s layers

• Study of Plate Motions

• Summary of Plate Driving Forces

The Major Platesboth continental and oceanic

How many plates are recognized by the Geophysicists? = 14 (see above)

GPS now tracks Plate Movements(via Mtn tops etc.) all moving in diff. directions

Types of Plate Boundaries

• What are the three types?

Peru/Chile trench

1.

2.

3.

Convergent boundary(oceanic crust vs oceanic crust)

e.g. Marianna Trench• both

1 crust Subducts

MariannaForms Mariana Is.

Convergent boundary(oceanic crust vs continental crust)

e.g. Peru/Chile & the Andes Mtns

Nasca Plate

S. AmericaPlate

Formation of Andes Mtns

Melting of Subducted oceanic crust

Convergent boundary(continental crust vs continental crust)

e.g. the Himalayas Mtns

Mt. Everest

http://www.youtube.com/watch?v=xL6sKtG2UVs

How can Rigid plates can move about a sphere?

• Because of the existence of . . .– Transform Faults

Relieves built up tension in spreading plates. .

Transform Boundaries (faults)-offsets the stress of expanding plates

Mid ocean ridge

Transform Boundaries (faults) -offsets the stress of expanding plates

Hot Spots & Mantle Plumes• What are hotspots?

– Stationary locations in the asthenosphere

where magma breaks through

http://www.youtube.com/watch?v=GrONBPEgxTc&feature=related

http://www.youtube.com/watch?v=hOCfb9ox_90

Diamond HeadHawaii

e.g. Hawaiian Islands

Or Tahiti (Bora bora)

Hot Spots (Literally) Tahiti

Opening and Closing ofOcean Basins (over geologic time)

• The Wilson Cycle– Seafloor spreading

(stable crust)

(formation of . . .. . .Mid Ocean ridge) rains fill in etc.

Formation of an Ocean Basine.g. the Atlantic

Opening and Closing ofOcean Basins (over geologic time)

Closing of an Ocean Basin

e.g. N. Pacific ~ Eventually

Ocean Seafloor ageN. Pacific basin eventually swallowed

Old

New

OUTLINE

• A Theory of Earth

• Historical Development of Plate Tectonics

• Earth’s layers

• Study of Plate Motions

• Summary of Plate Driving Forces

Plate Driving Forces(i.e. the “forces” that “move” the “plates”)

• What are the two major Models?

1) Convection modelConvection currentsw/i asthenospheredrive plate motions

2) Ridge-Push, Slab-Pull Model

MagmaSinks b/c cool/dense

Magma rises b/c hotLess/dense

(plain)

(plain)

hotcoolerNew

crust oldcrust

Major Concepts

END on a Nice Note: Tahiti –Bora Bora

GPS now tracks Plate Movements(via Mtn tops etc.)