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EXERCISES
EXERCISES
Examination and evaluation of real-time oceanographic data on the internet
PRELIMINARY
I: TECTONICS
and OCEAN BASINS
Earthquakes and Plate Tectonics
Spreading Rates
CA Earthquakes
Volcanoes
Topography of the Ocean Floor
History of Ocean Basins
II: OCEANS/ ATMOSPHERIC GASES
III: OCEAN/
ATMOSPHERE DYNAMICS
IV: INTEGRATED TOPICS
 
SPREADING RATES (contd.)

Rates of Seafloor Spreading at Mid-Ocean Ridges:

  • Aim: to determine and compare rates of seafloor spreading at different divergent margins and assess their global variability.
  • Website: http://www.ldeo.columbia.edu/~menke/plates2.html
  • Content: the NUVEL-1 Plate Velocity Parameters calculator permit determination of the rates and directions of spreading at mid-ocean ridges.
    • Rates are given in terms of the movement of one plate relative to another in mm/year.
    • The direction (azimuth) of spreading is given as a compass bearing.

Procedures:
The site requires a response to the various options regarding choice of plates and location.
  • Select plates that border the chosen mid-ocean ridge.  Options are listed on pull-down menus:  African, Antarctic, Arabian, Australian, Caribbean, Cocos, European (i.e. Eurasian), Indian, Juan da Fuca, Nazca, North American, Pacific and South American.  (The Philippine and Scotia plates are not listed because they do not possess divergent boundaries.)
  • For geographic locations of individual plates see the global plate map at:    http://pubs.usgs.gov/publications/text/slabs.html
  • Enter values for the latitude (lat) and longitude (lon) on (or near) the ridge of interest as directed by the questions.  Note that they should be described with reference to North latitude and East longitude.  Thus, locations in the southern hemisphere or West of the prime meridian must be entered as negative numbers (i.e. 20°S = -20 and 115°W = -115)
  • Select the compute button, and the output will provide (among other information) the velocity of spreading in mm/year and the azimuth as a compass bearing (e.g. N280E = 280°).

Introduction to Questions on Seafloor Spreading Rates:
  • This is the third of four series of questions for this exercise, which are outlined in separate tables.
  • Reminder: you should submit your answers via oncourse.
Spreading Rates and Plate Motion (contd.) pt
Plate Velocity Calculations of Seafloor Spreading Rates
Assessment of the global variability of spreading rates on mid-ocean ridges requires multiple measurements of their rates at different locations. Hence, the first task is to determine the spreading rate in mm/year at the given locations.
http://www.ldeo.columbia.edu/~menke/plates2.html

mid-ocean ridge plate 1 plate 2 lat long
10. Red Sea Africa Arabian 20°N 40°E 1
11. Pacific-Antarctic Australian Antarctic
60°S
 150°E 1
12. East Pacific Rise
 Nazca Pacific 0° 105°W 1
13. Gulf of California N. American Pacific
25°N
 110°W 1
14. North Atlantic N. American European 45°N 30°W 1
15. South Atlantic S. American African 10°S 15°W 1
16. What is the range of spreading rates from Q.10-15 (i.e. faster & slowest)? 1
17. The width of the S. Atlantic between the continental shelves of Africa and S. America is now 5214 km at 10°S.  Calculate when the Atlantic started to form? [cf. question 15]  HINT 2
18. The Gulf of California is now about 156 km wide. How long will it be before it is 1200 km wide and truly an ocean? [cf. question 13]     HINT 2
19. What major assumption is central to your calculations in questions 17 and 18? Is it a reasonable assumption? (Bonus) HINT 4*
Determine the rate of spreading in mm/year and its azimuth (direction) at these five locations on the East Pacific Rise.  Select plate 1 as Nazca & plate 2 as Pacific. 
20.
lat
long
lat
long
lat
long
  (i) 0°
105°W
 (ii)
10°S
110°W
 (iii)
15°S
115°W
3
  (iv) 20°S
115°W
 (v)
25°S
110°W


2
21. What is the range of spreading rates along the East Pacific Rise? 
1
22. Are there significant differences in the direction or rates of spreading in this region of the East Pacific Rise?   HINT
1
Determine the spreading rate in mm/year and its azimuth (direction) for 3 locations along the Pacific-Antarctic Ridge.  Select plate 1 as Antarctica & plate 2 as Pacific. 
23.
lat long
 lat long    lat long  
  (i) 65°S
175°W
 (ii)
55°S
140°W
 (iii)
40°S
110°W
3
24. How variable are spreading rates along the Pacific-Antarctic Ridge? 
1
25. Describe and explain any significant differences in the direction or rates of spreading along this ridge?   HINT
1
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