Download SupportingMaterialForHotspotActivity_forSERC.v3

To Instructor: Students should be able to…
• 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.
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 - Inclination
-
+
Angle between Earth’s
surface and magnetic
field lines.
Earth’s Magnetic Field –
Inclination as a function of latitude
At Vancouver:
Latitude = 49 degrees North
Inclination = ~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)
“Fixed hotspot-moving plate” model
Resulting chain
of volcanoes
Lithospheric
plate motion
Mantle plume
For instructor:
Have class do activity 1 before continuing
Next 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?
>45 Ma
N-ward
0-45 Ma:
NW-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)
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
Corals?
Seamount
Age (Ma)
Inclination (º) Paleolatitude (º)
Detroit
78 Ma
60
42
No
Suiko
61 Ma
45
27
No
Nintoku
56 Ma
44
26
No
Koko
49 Ma
38
22
Yes
Hawaii
0 Ma
34
19
Yes
Inclination versus Latitude
90
Inclination (degrees)
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Latitude (degrees)
60
70
80
90
Corals?
Hotspot latitude versus Age
45
35
30
25
No Corals
Corals
20
15
80
70
60
50
40
30
20
10
Age (Ma)
 Moving plate + moving hotspot!
0
Latitude (degrees)
40
Demo for after this activity
(make the Hawaii-Emperor seamount chain):
Materials: blank overhead and overhead pens
You 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 chain
2. 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