• Explain what is required for a planet’s magnetic field to be generated by a dynamo.

• Describe the evidence that plates move, based on observations of magnetic patterns.

• Use paleomagnetic data to reconstruct past plate motion.• Compare the Earth’s magnetic field with those of other

planets and explain what the observations of those planets reveal about internal composition and structure.

To Instructor: Students should be able to…

The hotspot activity is directed toward achieving the 2nd and 3rd of these goals. Prior information should include generation of Earth’s magnetic field, magnetic reversals, sea floor spreading, and the development of remanent magnetism, both in igneous and sedimentary rocks/sediments.

See “notes” pages under subsequent slides for information

Earth’s Magnetic Field - InclinationEarth’s Magnetic Field - Inclination

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Angle between Earth’ssurface and magneticfield lines.

Earth’s Magnetic Field – Inclination as a function of latitude

Earth’s Magnetic Field – Inclination as a function of latitude

At Vancouver: Latitude = 49 degrees NorthInclination = ~67 degrees

Magnetic inclination: evidence for WHERE rocks formed

HOT SPOT VOLCANOES:Chains of volcanoes(and single volcanoes)on the sea floor

The Mantle Plume Hypothesis

1. Hot spots form where narrow plumes rise by convection from the core-mantle boundary

2. The plume locations are stationary in the mantle

IF this is true, what would the evidence look like?

Hotspot tracks(animation)

Lithosphericplate motion

Mantle plume

Resulting chainof volcanoes

“Fixed hotspot-moving plate” model

For instructor:Have class do activity 1 before continuingNext slide, discuss answers to activity 1

What does the “fixed hotspot – moving plate” model imply about the direction of motion of the

Pacific Plate in the past?

0-45 Ma:NW-ward

>45 MaN-ward

Did this happen?

How are hot spots?

(and how could we tell?)

TESTING THE FIXED HOTSPOT MODEL WITH INCLINATION

How are hot spots?

What do you think happened?

Seamount Age (Ma) Inclination (º) Paleolatitude (º) Corals?

Detroit 78 Ma 60 No

Suiko 61 Ma 45 No

Nintoku 56 Ma 44 No

Koko 49 Ma 38 Yes

Hawaii 0 Ma 34 Yes

Data from Tarduno et al., Science, 2003

Seamount Age (Ma) Inclination (º) Paleolatitude (º) Corals?

Detroit 78 Ma 60 No

Suiko 61 Ma 45 No

Nintoku 56 Ma 44 No

Koko 49 Ma 38 Yes

Hawaii 0 Ma 34 Yes

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27

26

22

19

Moving plate + moving hotspot!

Hotspot moving south

Hotspot mostly stationaryCorals

No Corals

Demo for after this activity (make the Hawaii-Emperor seamount chain):

Materials: blank overhead and overhead pensYou be the hotspot (pen). Get a volunteer to be the plate

(overhead).Ask the volunteer to move the “plate” across the overhead

projector to the NW (like the Pacific Plate)1. You be a “fixed” hotspot. Result: linear chain2. You be a hotspot that moves south for a while, then

becomes stationary. Result: something very like the Hawaiian-Emperor Seamount Chain, with a sharp elbow