PROBLEM SET 1
1. Spend an hour or so in the Geology Library
with Bruce Heezen and Marie Tharp's physiographic map
of the world ocean floor (on reserve) and Lowman's plate tectonic map
(attached). Trace your way along all the
systems of plate boundaries, checking their names and which plates they
separate, until they are familiar to you.
(A) Identify two examples each of convergent,
divergent, and transform plate boundaries with contrasting physiographic
expressions. How can you explain these
differences?
(B) Are there other first-order physiographic
patterns within the plates or along the plate boundaries that particularly
strike you? What tectonic phenomena
might explain these patterns? (There's
no "correct answer" to this one!)
(C) Compare Heezen and
Tharp's 1963 map with a more recent representation, J.R. Hiertzler's
"Relief of the Surface of the Earth", based on digital topography
data (also on reserve). What
similarities and differences do you observe?
2. Help us test-drive our brand-new tectonic map
tool, the "Jules Verne Voyager, Jr."
(http://jules.unavco.ucar.edu/VoyagerJr/Earth). Select a plate boundary of your choosing,
zoom in by clicking on the map area, and use the map tool to examine a series
of base maps and overlays for the plate boundary. Briefly, describe the area in terms of
(a) regional physiography, (b) stress orientation,
(c) strain rate, (d) earthquake and volcano distribution, and (e) plate
boundary motion. Consult the
"Education Site" (http://www.dpc.ucar.edu/VoyagerJr/jvvjrtool.html)
for additional background information about the map tool. And provide us with some feedback on what you
think of the map tool itself. What works
and what doesn't?
3. Consider an idealized oceanic basin abutting
a continent. Assume densities of sea
water, crust, and mantle of 1.03, 2.9, and 3.3 x 103 kg/m3,
respectively, an ocean-basin depth of 5 km and an oceanic crustal
thickness of 6.6 km. How thick would you
expect adjacent continental crust to be if it were in isostatic
equilibrium with the ocean?
4. Calculate the depths and densities beneath a
5 km-high mountain chain in Airy isostatic
equilibrium with a 35 km thick continental crust (density = 2.8 x 103)
and a 3.3 x 103 km/m3 mantle by using the hypothesis of
(a) Pratt, and (b) Airy.
5. A mountain range 4 km high is in Airy isostatic equilibrium.
Assume crustal and mantle densities of 2.8 x
103 kg /m3 and 3.3 x 103 kg/m3,
respectively.
(a) During a period of erosion, a 2
km thickness of material is removed from the mountains. When the new isostatic
equilibrium is achieved, how high are the mountains?
(b) How high would they be if 10 km
of material were eroded away?
(c) How much material must be eroded
to bring the mountains down to sea level?
6. Cox & Hart: Problem 9-1.
Do sections a,
c, e, g, k, m, o, r, w, y. Use
stereo net where necessary, and consult Chapter 3 to refresh your stereonet techniques.
7. Cox & Hart: Problem 9-3.
8. Cox & Hart: Problem 9-4.
9. Because of the errors associated with individual
measurements, the paleomagnetists typically treat
their measurements statistically, using a large number of samples. Confidence limits should be indicated along
apparent polar wander (APW) paths, but seldom are. In Cox & Hart's Table 9-1, the radius of
a small circle of 95% confidence (a95)
is given for each of the pole determinations.
Using a stereo net centered on the geographic north
pole to represent the globe, plot the positions of each pole in the
North American APW curve, and draw the a95 circle
around each pole. [Note: Because degrees
of "latitude" on the stereo net are approximately constant, you can estimate the radius of the a95 circle using these small circles.] Repeat for the Eurasian APW curve.
(A)
What can you say about the paleomagnetic
evidence for drift of
(B)
What are the sources of scatter in the individual pole determinations?