NAME: ___________________________
12.001 QUIZ 2: Rock Deformation, Rheology, and Plate Tectonics
MARCH 31, 2010
ANSWER ALL QUESTIONS IN THIS QUIZ BOOKLET AND HAND IN
NOTHING BUT THIS BOOKLET.
YOU HAVE UNTIL 1:55 TO COMPLETE THIS QUIZ.
Question 1
Question 2
Question 3
Question 4
Question 5
Question 6
Question 7
(Bonus
___/40
___/20
___/20
___/20
___/40
___/20
___/40
___/10)
Total
___/200
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PART I: ROCK DEFORMATION AND RHEOLOGY (80 PTS)
Question 1: (40 PTS)
A. (30 pts) On the axes of stress vs. depth, sketch and label the brittle and ductile yield curves for continental
crust with a geotherm of 25°C per kilometer. Label the region of elastic deformation.
differential Stress
0
10
20
depth (km)
30
40
50
60
70
80
90
100
B. (10 pts) Draw the yield curve that would result if the geotherm were lowered to 10°C per kilometer, keeping
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all other variables the same. Draw the new yield curve on top of the original yield curve, using the original
curve for reference. What has changed and why?
differential Stress
0
10
20
depth (km)
30
40
50
60
70
80
90
100
Question 2: (20 PTS)
Explain one method for inferring the viscosity of the upper mantle from geologic evidence. Give the
approximate viscosity (in SI units) estimated from this method. Compare this value to the viscosity of honey
you estimated in your lab exercise.
Question 3: (20 PTS)
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Draw a diagram of stress (y-axis) vs. strain (x-axis) for a rock undergoing compression. Label and define the
elastic region, the plastic region, and the fracture point.
PART II: PLATE TECTONICS (120 PTS)
Question 4: Short Answer (1-2 sentences) (20 PTS)
A. What is the distinction between the terms crust and lithosphere? (2 pts)
B. What is the distinction between the lithosphere and the asthenosphere? (2 pts)
C. What is the age of the Earth, to two decimal places? (2 pts)
D. Approximately how old are the oldest intact continental rocks? (2 pts)
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E. How old is the oldest oceanic crust? (2 pts)
F. Why do the ages in D. and E. differ? (2 pts)
G. What is the upper mantle made of? Give the dominant rock name, its mineral components, and whether it is
solid or liquid. (3 Pts)
H. Name three factors that affect how a rock responds to stress. (3 Pts)
I. Name the type of stress that causes the pattern of faulting shown in cross-section below. (2 Pts)
Question 5: (40 PTS)
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A. (15 pts) Attached to your quiz you’ll find maps with data similar to what you used in your plate tectonics lab.
On the blank map provided, draw plate boundaries showing the directions of relative plate motion, and give the
name of the type of plate boundary.
B. (10 pts) What type of melting is causing the volcanism? Illustrate your answer by drawing a phase diagram
for mantle rocks in temperature vs. depth space, and indicating the change in conditions that is causing melting.
C. (10 pts) Draw a cross-section along the transect marked A-A’ in the figure. Indicate plate movement,
directions of mantle convection, and earthquake and volcano distributions.
Question 6: (20 PTS)
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What is thought to be the main force driving plate tectonics, and what is the main observational evidence for
this view?
Question 7: (40 PTS)
Describe the sequence of tectonic events that make up the Wilson Cycle. For each event, explain what kinds of
regional tectonic systems or plate boundary zones are formed, and give an example from the present or the
geologic past.
Bonus: (10 PTS)
Name one line of evidence uncovered before the 1960s that supported plate tectonics.
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