Study questions and exercises

Write the answers to the questions in a word document and send it to christian.stranne[at]geo.su.se. Your document should be named with your name and the moment according to the following convention: firstname_lastname_MomentX.docx
Once we received your answers you will get a correction sheet. Correct your own answers using the sheet and where you have questions, please write them in an email to the course email. When you have answered all questions you will also get a code to open the lecture(s) of the next Moment.
The study questions and exercises are only for your own learning and the code system is intended to help you following the course structure and to set your study pace. It is your own responsibility to follow this scheme.

Study questions and exercises on Moment 7

  1. What is the approximate direction of the Earth’s magnetic field relative to the sea level at a) the geographic South Pole, b) the geographic Equator, c) the geographic North Pole?
  2. What is the difference between the geographic and the magnetic poles? Why aren’t they the same?
  3. What is susceptibility? How can an apparently low- or non-magnetic rock such as haematite give rise to a strong magnetic anomaly?
  4. Why are magnetic anomalies over crystalline continental crust higher in amplitudes and much more variable than over oceanic crust?
  5. What are the necessary data reduction steps (corrections) in magnetic survey data?
  6. Why is a magnetic anomaly outside the magnetic equator not symmetric or centered over the causing body?
  7. What is a magnetic domain?
  8. Explain what happens with the magnetic domains when a magnetic material is placed in an external magnetic field that is: a) weak, b) strong enough to cause remanence in the material.
  9. Which mineral groups have remanent magnetization?
  10. Why will a continuous rock body with high susceptibility such as a lava flow or a large sill not cause any magnetic anomaly in its interior parts?
  11. Draw a sketch explaining the difference between ferro-, ferri- and antiferromagnetism, and explain what they mean in terms of dipole arrangement.
    • a) Give the respective IGRF Total field values and yearly change in declination at Mean Sea Level for Stockholm (Sweden), Kiruna (Sweden), Longyearbyen (Svalbard, Norway), and McMurdo Station (Antarctica) for the date 2016-09-01.
    • b) Why do we need to specify a date – what is slowly changing with time, and what is this change called?
  13. Look at the magnetic anomaly map on slide 20, and compare with the geologic map on slide 21. Answer the following:
    • a) Where in the map do the anomalies generally have higher amplitude and shorter wavelength?
    • b) What type of rocks corresponds to these anomalies?
    • c) In the Labrador Sea, there is a large region in the geologic map interpreted as oceanic crust with an extinct spreading center. What features in the magnetic map could have contributed to this interpretation?
  14. How is marine magnetic anomaly patterns evidence for the Plate Tectonic theory?
  15. How is the record of pole reversals utilized in core chronology?