Download GEOL 101 Lab 2: Plate Tectonics

GEOL 101 Lab: Plate Tectonics Name:
Answer sheet. These are not the lab instructions. This is just the answer sheet.
What to turn in:
1. The table of each magnetic reversal’s age, distance orthogonally (at right
angles) from the Juan de Fuca ridge, and rate of spreading from the ridge, in
both km/Myr and cm/yr. (See lab instructions – it will tell you how.)
2. The graph of age (horizontal) and distance from ridge (vertical) for the Juan de
Fuca Ridge magnetic anomalies. Note that this graph must have two curves, east
of the ridge and west of the ridge, on the same graph grid. (See lab instructions.)
3. The graph of age (horizontal) and distance from hot spot (vertical) for the
Hawaiian Islands-Emperor Seamount Chain, with a best-fit or hand-fit line that
goes through the origin. (See lab instructions.)
4. This answer sheet with your name and all your answers on it. Only answer the
questions after you have followed all the lab instructions and your graphs are
completed.

The edge of this piece of paper must show your age scale, in 1 million
year spacing between tick marks, that you used to get the ages of the
magnetic reversals on the Juan de Fuca Ridge map.
You have a choice: by pencil and paper, or on computer. You can make your Juan de
Fuca table and graphs, and your Hawaii-Emperor graph, by hand on paper. Or you
can do so using an Excel spreadsheet and one of the DESKTOP computers in the
room (must use a desktop computer if you want to print).
If you use Excel, do NOT print out and turn in hard copy of the Hawaii-Emperor
table, only print the Hawaii-Emperor graph, or you will lose points.
If you use pencil and paper, write the Hawaii data down on paper, writing only those
numbers used in the graph (plus a title and column headings, as must always be
included with a table). Add this table to what you turn in.
In either case: (1) Your name must be on every page you turn in. (2) The lab you
submit must be stapled together with this answer form on top, then the table(s) and
graphs, and (3) all tables and graphs must be correctly labeled, including units.
Part 2: Juan de Fuca Ridge (Skip Part 1)
DON’T ANSWER THESE QUESTIONS UNTIL YOU HAVE PRODUCED YOUR
GRAPHS. This is just the answer sheet. Leave it aside until you have completed the
lab by following the lab instructions, which are online.
1. According to plate tectonic theory, would the plates on either side of a mid-ocean
ridge, at a particular point on the ridge, be spreading at close to the same rate?
2. According to plate tectonic theory, would the spreading rate be the same on one
end of the ridge as at the other end of the ridge? Explain your answer.
3. What geological structure, common in oceanic crust, may disrupt the spacing of
magnetic anomalies on the ocean floor?
3. On the Juan de Fuca map, what is represented by the dark, straight lines that mark
offsets in the magnetic anomaly patterns?
4. The theory of seafloor spreading, which is part of plate tectonics theory, predicts
that plates spread away from divergent plate boundaries at close to equal rates on
either side of the ridge. If that is true for the Juan de Fuca Ridge, then the two
lines on your graph should be more or less on top of each other. Are they?
5. If they are not, do you think it is because the plates have not been spreading
symmetrically, or do you think it might be largely due to uncertainties in your
measurements due to complicating factors such as the faults that offset the
magnetic anomalies?
6. To the nearest 0.1 cm/yr, at what rate has the Pacific Plate been spreading away
from the Juan de Fuca Ridge over the last 9.7 Ma? (The Pacific Plate is the plate
on the west side of the ridge.)
7. To the nearest 0.1 cm/yr, at what rate has the Juan de Fuca Plate been spreading
away from the Juan de Fuca Ridge over the last 9.7 Ma? (The Juan de Fuca Plate
is the plate on the east side, or right-hand side, of the ridge.)
Part 3: Hawaii-Emperor
8. State a reasonable hypothesis why the Emperor seamount chain is oriented
differently (as seen on a map) from the Hawaiian island chain.
9. Not all the data points on your graph fall onto a single straight line. Does this
prove that the Pacific Plate is not really moving across the hot spot? Why?
10. Give a plausible explanation of why some of the data points on your graph are
scattered above and below each other, rather than spread out on a single line.
11. What does the slope of the line correspond to? (Slope is rise over run, or Y value
divided by X value. Look at the Y units and divide them by the X units. What do
you call the result?)
12. Assume that the graph portrays the rate of motion of the Pacific Plate across a
stationary Hawai‘ian hot spot. If so, has the Pacific Plate always moved at a
constant speed? (In other words, is the slope of the line constant?)
13. Over what interval of time is the slope of the graph steepest? (In other words, at
what interval of time would the Pacific Plate have been moving the fastest across
the hot spot?)
14. Suggest an independent method of measuring the velocity of motion of the Pacific
Plate, which could be used to compare with the rate of motion determined here by
the Hawai‘i-Emperor volcano age-distance data.