SO461 Geological Oceanography

Spring 2006 Test 1

 

Diagrams

4 @ 20 points

80

 

Short answer

4 @ 5 points

20

 

Total

 

100

 

 

Authorized reference:

  1. This test will be open book.  Students can use their own copy of the textbook, with any notes they have permanently written in it.  No papers can be attached to the text, and class notes and handouts will not be allowed. Books will not be shared during the exam.
  2. Calculators will not be allowed.  For the calculations, you may set it up and leave the answer in terms of a sum, product, or quotient, or you can make reason simplifications to get a rough idea of the answer.

 

Short Answer: The questions should be answered with several sentences (no more than a short paragraph). You must answer four of the five questions.

Diagrams: These should clearly indicate understanding of the procedures and concepts involved, and should be well thought out with appropriate terms and details to support your answer.  

 

Budget your time.  If you try to look up everything in the text book, you will run out of time.  Do not leave anything blank, and note that I am looking for an understanding of the important concepts and appropriate use to terminology.

Termination of a fossil continent-ocean fracture zone imaged with three-dimensional seismic data: The Chain Fracture Zone, eastern equatorial Atlantic. Richard J.Davies, Christopher J.MacLeod, Richard Morgan and Sepribo E. Briggs, pages 641–644, Geology Volume 33, Number 8, August 2005

Figure 1.  The diagram above shows a seismic reflection line in the Atlantic Ocean.  The horizontal axis is in km as the ship sailed (see scale bar), and the vertical axis is in milliseconds TWTT.  To make your calculations simple, we are assuming the major reflectors are horizontal and occur an easy to calculate positions on the vertical axis.

 

Assume that the yellow region at the top of the diagram represents the water.  If it ends at a TWTT of 9000 ms (= 9 sec), how deep is the water?  Explain and list any assumptions.

1500 m/sec * 9 sec / 2 = 6.75 km 

Assume the reds and blues (between reflectors 1 and 2) on the left side of the profile are marine sediments, the greens are the oceanic crust, and that reflector 3 marks the Moho which occurs at a TWTT of 10,000.  About how thick do you think this crust is, and do you think it’s thicker on the east or west side of the profile?  Explain and list any assumptions.

1 sec TWTT.  In igneous ocean crust this would be 3.4 to 7 km/sec, or 1.7 to 3.5 km.  East side is thicker (longer TWTT time, and it’s all faster igneous crust (layers 2 and 3) instead of slower Layer 1 sediments) 

What kind of faults do you see?  How can you tell, and what kind of plate tectonic environment would they form in?

Figure 2.  The three magnetic anomaly profiles below were acquired in the same region, and all have the same horizontal scales (in km) and vertical scales (in nannoteslas).

 

 

 

 

 

 

What are these magnetic profiles actually measuring?

 

On each profile, mark the location or the ridge or indicate the direction in which you would look to find the ridge that created this seafloor.

 

Label at least two anomalies on each profile with your estimate of the age in millions of years.

 

How does the spreading rate vary for each profile?  For one profile, show how you would calculate it, and then indicate whether the other two would have faster or slower spreading rates.

 

Top:  210 km / 28 Ma = 7.5 km / Ma

Middle: 120 km / 10 Ma = 12 km / Ma

Bottom: 100 km / 12 Ma = 8.3 km / Ma

 

What is an Euler pole, and how do these profiles relate to one?

 

Answer --note the age scale below each profile.

 

 

 

 

 

Figure 3.  The diagram above  shows a sequence of rocks that you found while walking through the scenic mountains of Oman on your graduation leave.  The thickness scale is in meters.  Discuss what you can infer about the geologic history from these rocks.  For full credit you should have something to say about each rock type.

 

 

Figure 4.  The diagram above shows the earthquake focal mechanisms for a region in the Indian Ocean that is about 350 km across.

 

Pick two representative earthquakes that will do the best job of explaining what is happening, and show the likely orientation of the fault plane and the type of fault involved.  Be specific and include numbers; list and defend any assumptions you make.

 

A fault plane has a dip and a strike.  There are two possible faults planes for each beach ball.  You should list BOTH, and then says how both are likely, or if you think one is more likely.

  

On the diagram below, sketch a possible plate boundary or boundaries and indicate the plate motions suggested by the earthquake data

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Short Answer:  Briefly discuss 4 of the following 5 terms.  Your answer must explain what the term means, and you must use one of the figures from the first part of the exam in your explanation.  Clearly refer to the figure you are referring to.