Name: Reg. lab day: Mo Tu W Th

Geology 1023 — Lab #1, Winter

Plate Tectonics

1. Figure 1 (on the following page) shows the global distribution of earthquake epicentres.

a) Using this map as a base, Fig. 1.11 in your text (p. 16), and the large map on the wall of the lab, draw on all the plate boundaries, using colours as follows:

diverging – red converging – green transform – blue

b) Put arrows on the San Andreas Fault to indicate the sense of motion.

c) Write names on the 6 largest plates. 2. Figure 2 shows the continents in a polar projection, as well as the apparent polar wander

(APW) path for Europe for the Cambrian to the Cretaceous. The six arrows on the North American continent each represent the direction of remnant magnetism at the outcrop located at the tip of the arrow head. Magnetic inclination has been measured at each outcrop and translated into distance from the outcrop to the paleopole for each time period, as listed below the figure.

a) Plot the location of the magnetic paleopole for each outcrop, and join the poles.

You have just drawn the apparent polar wander curve for North America!!!

b) Using a sheet of tracing paper, draw the outline of North America, the present north pole (N), and the North American apparent polar wander curve. Rotate the North American APW curve until it coincides with the European APW curve.

Based on this exercise: 1) When were Europe and North America joined? ___________________________________________________________ 2) When did they separate? ___________________________________________________________

See page 2

See page 2 See page 2

Cambrian to Triassic

Triassic

Answer key

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Plate Tectonics — Answer key Page 4 of 6 3. Figure 3 shows the stages in the formation of an ocean basin, such as the present Atlantic

Ocean.

a) Is the ocean crust at “C” older or younger than the ocean crust at “W”?

_________________________________________________________ b) Assume that figure 3c represents accurate conditions, and that the basalt at “C”

has an average age of 10 million years. What is the average rate of separation of the continents, in cm/year, during the past 10 million years?

c) Assuming that the rate of sea-floor spreading has not changed through time, what is the age of the sea floor at “W”?

4. Figure 4 shows magnetic anomaly profiles recorded along 5 ship’s tracks across the

Reykjanes Ridge, south of Iceland.

a) Using different colours colour the normal polarity events on the magnetic polarity time scale on figure 4 (use red for the youngest). (Leave the reversed polarity events uncoloured.)

b) Using the same colours as on the scale, draw and colour magnetic “stripes” on the

map by correlating normal and reversed polarity events between the profiles.

c) What is the rate of sea-floor spreading (in cm/year) on the Reykjanes Ridge?

younger

C-C = 14.5 mm x 50km/mm = 725 km 725 km x 100,000 cm/km = 72,500,000 cm 72,500,000 cm/10,000,000 yr = 7.25 cm/yr (6.75 – 7.5 cm/yr accepted)

W-W = 107 mm x 50km/mm = 5350 km 5350 km x 100,000 cm/km = 535,000,000 cm 535,000,000 cm/7.25 cm/yr = 73,800,000 yr = 73.8 Ma (70-80 Ma accepted)

Distance = 136 – 175 km, time = 10–10.2 Ma Rate = 1.3 – 1.75 cm/yr

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