Past plate motions - The Solid Earth - page 93

3. If the direction of magnetization of the lavas of Problem 2 is due west, calculate the
position of the pole of the Earth's magnetic field at the time the lavas were erupted.
What does this indicate about the continent on which these lavas occur?
4. If the measurement of the angle of inclination of the lavas of Problem 2 is in error by
5 ◦ ,what is the subsequent error in the calculated palaeolatitude?
5. Down to what depth can (a) oceanic lithosphere and (b) continental lithosphere be
permanently magnetized? (Hint: see Chapter 7.)
6. (a) Use Fig. 3.12 to calculate a spreading rate for the South Atlantic. Is this a half-
spreading rate or a plate-separation rate?
(b) Using Fig. 3.12, estimate minimum and maximum spreading rates for the Pacific
during the last 80 Ma.
7. Calculate the minimum length of time that a reversal of the Earth's magnetic field
lasted if it was detected from sea-surface magnetic data collected in (a) the Atlantic
Ocean and (b) the equatorial Pacific Ocean.
8. Where is the oldest ocean floor, and what age is it? Discuss what may have happened
to the rest of the ocean floor of this age and why.
9. At any given latitude, what orientation of ridge gives rise to the largest-amplitude
magnetic anomalies?
10. At what latitude do magnetic anomalies due to magnetized oceanic crust have mini-
mum amplitude?
References and bibliography
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Winterer, D. M. Hussong and R. W. Decker, eds., The Geology of North America, Vol. N,
The Eastern Pacific Ocean and Hawaii . Boulder, Colorado: Geological Society of
America, pp. 21-7.
Atwater, T. and Severinghaus, J. 1989. Tectonic maps of the northeast Pacific. In E. L.
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