SO461
Geological Oceanography
Fall 2007,
Test 2
|
Short
answer |
4
@ 10 points |
40 |
|
|
Longer
answer |
3
@ 20 points |
60 |
|
|
Total |
|
100 |
|
Short Answer: The questions should be answered with
several sentences (no more than a short paragraph). You must answer four
questions, and have a choice from five.
Longer Answer: These should clearly indicate
understanding of the procedures and concepts involved, and use correct and
appropriate terminology.
The exam is open book, which
includes any notes permanently written in the book. No other references or calculators are
allowed. Do not leave anything blank,
and note that I am looking for an understanding of the important concepts and
appropriate use to terminology. An
answer than does this will get more credit than finding and copying a sentence
in the book that includes the word.
Budget your time. If you try to look up everything in the text
book, you will run out of time.
Short
Answer. Answer 4 of the 5 questions in this section,
for 10 points each.
1. The diagram below shows an earthquake at
occurred on a fault. The fault appears
to offset two linear features, A and A’.
·
What do you think is the orientation (dip and strike) of the
fault? Why can you say this? There
are two possible strikes, about N0 and N90E, with dips of about 85W and 85N
respectively. The East-West strike is more likely because it is parallel to the
fault trace.
·
What kind of fault do you think this is? Be specific, and discuss the geometry shown.
Transform fault.
·
Could there be a fault with a similar geometry but different focal
mechanisms?
2. The two diagrams below cover areas of the
seafloor about 1250 km across. Discuss
the features you see in the diagrams, and what accounts for the differences
between the two areas.
3. Use a sketch diagram to show how we
classify the metamorphic rocks, and the major groupings in our classification. Are there any possible cases where it would
be understandable to take gneiss for granite?
4.
The diagram below shows a map of a plate boundary, and the velocities between
the two plates along the boundary at four points in the hot spot reference
frame. You can make any reasonable
assumptions you want, and approximate values.
·
Given the geometry, what kind of a plate boundary do you think this
is? Why?
·
How do we define plate motions, and what can you say about the plate
motion between the two plates from the velocity pattern?
 |
Plate motion at each
of the 4 locations.
While the 72 mm/yr is the maximum in this area, we do not know that it is 90 degrees from the Euler pole. We do not know where the Euler pole is, because the volcanic arc does not lie on a great or small circle related to the Euler pole. |
5.
The diagram below shows a seismic reflection line from the offshore
·
If this is related to transtension or transpression, what does that
mean?
·
Why does the scale on the right side say water depth (m), even when it
records the returns form the ocean crust below the seafloor?
·
What do you think is the actual depth at the bottom of the record? What assumptions would you have to make for
this assessment?
Longer Answer.
Answer all 3 questions in this section, for 20 points each.
The
map and east-west cross section above show the distribution of earthquakes
somewhere on earth, and nine focal mechanisms.
·
Could the two diagrams represent the same area? Why or why not?
·
What kind of plate boundary (or boundaries) are on the map?
·
What type(s) of fault occur in this region, and how do they relate to
the plate boundary (or boundaries)?
·
Would igneous rocks be created in this region? Where and why?
· Would metamorphic rocks be created in this region? Where and why?
 |
Earthquakes color coded by focal mechanisms. |
 |
Earthquakes color
coded by focal mechanisms.
Note the thrusts are all very shallow, and occur both along the subduction zone and in the orogenic belt to the east. |
The
two diagrams below show a map with three plates, and a velocity diagram showing
the plate motions in the hot spot reference.
|
Boundary |
Type |
Explain reason |
|
A-B |
|
|
|
B-C |
|
|
|
A-C |
|
|
Which
boundary will show the fastest motion, and why can you say this?
3. Discuss how recent technology allows us to
compute instantaneous rates of plate rotation.
How do these poles differ from total reconstruction poles and stage
poles, and which poles we would want to use to create a movie showing the
breakup of the Pangea supercontinent?