Introduction to Plate Motions

Change Program version to geology

Plate motions

• All plate motions can be modeled as a rotation about an Euler pole.
• The motion includes the location of the Euler pole, and the rotation rate.

Plate models

• All plate models are relative to something that is fixed.  This can be a single plate, the hot spots, or something else the author has reason to believe has not moved.
• Three kinds of poles:

Part 1.

• File,   Geology lab, Plate rotations
• You will get:

• Outlines of the major continental crust blocks. Note that continental crust includes the shelves where these are wide.
• Plate boundaries.
• A small control window
• Do an Arbitrary rotation
• Pick the Option in the upper left corner of the form.
• Pick the plate to rotate by selecting its name.
• Adjust the pole of rotation and rotation amount in the control window
• Pick "Rotate"
• Select "Pick Pole" and then click on the pole's location on the map.

Answer the following questions (India is a good continent to rotate):

• What happens when you rotate about the north geographic pole?
• What happens when you rotate about the south geographic pole?
• What is the difference between rotating a positive and a negative angle?
• What happens when you rotate about a point on the equator?
• What happens when you rotate about a point within the continent?
• What mathematical convention governs the rotation pole and direction?  (Note that there is a north and south rotation pole possible; which do we use?)
• Where on the plate will there be the fastest and slowest motions?  Which rotation above helped you to see that?

Part 2.

• Do a Current vectors operation, picked on the upper left corner of the form.
• Pick the NUVEL-1A as the "Current rotation model", and North America as the continent.
• Where is the pole of rotation?
• How could you see this by plotting vectors at various locations around the continent?
• If you change the current rotation model, what happens to the Euler pole, and the rotation vectors?  How is this possible?

Part 3.

• Keep Africa fixed, and try to rotate North America and South America back into place.
• Do this using an Arbitrary rotation

• What Euler pole works best to rotate Africa back to South America?
• What Euler pole works best to rotate South America back to Africa?
• What Euler pole works best to rotate North America back to Africa?
• Which pair has a faster angular rate of rotation?

Part 4.

• Create a movie of past plate motions.
• Pick the Past total poles option on the upper left corner of the form..
• Pick the total poles model to use (you can use either).
• Pick the movies button on the bottom.
• You can change the playback speed, single step, and stop the playback.

• What continent moves the fastest?
• What is the difference between the two models?

Part 5.

• Look at the motion of two plates at a boundary.
• Two plate motions.  Note there are two worked examples, for boundaries of the Juan de Fuca plate.
• Subset & zoom on the map to cover just the Indonesian trench.
• Pick "Current rotation model" (APKIM8.80)
• Pick the two plates (Australia and Eurasia)
• Pick Velocity diagram, Uncheck label velocities, and uncheck Resultant vector
• Pick the "Motion" button
• Double click at a point along the boundary.  From the velocity diagram or the two vectors, understand how to get the resultant.
• Zoom out to show entire data set.
• Repeat for a location on the Mid Atlantic Ridge.  Insure that you consider both the ridge and transform segments.