Plate Tectonics

1. Plate Tectonics By L.M. Gahagan Rough draft October 5, 2001

2. Historical Aspects(From Cox, 1973) Key events • mapping of seafloor topography (presence of guyots, mid-ocean ridges, etc.)

3. Seafloor topography (Smith and Sandwell 1997)

4. Historical Aspects(From Cox, 1973) Key events • mapping of seafloor topography • measuring the seafloor’s magnetic field (‘magnetic stripes’)

5. ridge Magnetic ‘stripes’ along the Reykjanes Ridge. From Vine 1966

6. Historical Aspects(From Cox, 1973) Key events • mapping of seafloor topography • measuring the seafloor’s magnetic field • timing the north-south flips of earth’s magnetic field (paleomagnetism)

7. Historical Aspects(From Cox, 1973) Key events • mapping of seafloor topography • measuring the seafloor’s magnetic field • timing the north-south flips of earth’s magnetic field • accurate location of earthquakes (indicate present-day plate boundaries)

8. Earthquake epicenters (Engdahl et al. 1998) and Holocene volcanoes (Smithsonian Global Volcanism Project)

9. Key Papers Wegener (1912) – Continental drift: continents rafting through the upper mantle. Menard (1952), Dietz (1952) – fracture zones Irving (1956), Runcorn (1956) – used paleomagnetic data to show polar wandering and motion between plates. Ewing and Heezen (1956) – presence of a rift valley at crest of most mid-ocean ridges. Dietz (1961) – coined the term “sea-floor spreading” Hess (1962) – Plate tectonics: convecting mantle passively carries the continents. Vine and Matthews (1963) – magnetic stripes of the ocean sea floor are created by the magnetization of oceanic crust as it is formed at the mid-ocean ridges. The older crust moves away from the ridge as new crust forms.

10. ridge Magnetic ‘stripes’ along the Reykjanes Ridge. From Vine 1966

11. ‘picks’ synthetic wiggle chron Interpretation of marine magnetic anomalies. From Barckhausen et al. 2001.

12. Inpretation of magnetic anomalies from ship-track wiggles, (Barckhausen et al. 2001).

13. Key Papers Bullard et al. (1965) – fit of the South Atlantic plates; use Euler theorem for rotating plates; Wilson (1965) – division of earth into plates and importance of fracture zones for plate motion

14. Division of earth into plates (Wilson 1965).

15. Key Papers Bullard et al. (1965) – fit of the South Atlantic plates; use Euler theorem for rotating plates; Wilson (1965) – division of earth into plates and importance of fracture zones for plate motion McKenzie and Parker (1967) – worked with poles of rotation to describe plate motion on a sphere

16. Use of Euler poles to rotate plates on a sphere (Morgan, 1968).

17. Key Papers Bullard et al. (1965) – fit of the South Atlantic plates; use Euler theorem for rotating plates; Wilson (1965) – division of earth into plates and importance of fracture zones for plate motion McKenzie and Parker (1967) – worked with poles of rotation to describe plate motion on a sphere Morgan (1968) – use of fracture zones in plate motion; map of the major plates

18. Major plates as mapped by Morgan (1968)

19. Key Papers Bullard et al. (1965) – fit of the South Atlantic plates; use Euler theorem for rotating plates; Wilson (1965) – division of earth into plates and importance of fracture zones for plate motion McKenzie and Parker (1967) – worked with poles of rotation to describe plate motion on a sphere Morgan (1968) – use of fracture zones in plate motion; map of the major plates Le Pichon (1968) – used magnetic stripes and euler poles to reconstruct the plates

20. Plate Tectonics Today explains many geologic phenomena - volcanic/earthquake activity - trenches, mid-ocean ridges - hotspot tracks - similarity between fossils & geologic rock assemblages across oceans

21. Pangea • most scientists agree on the general configuration of Pangea

23. Pangea • most scientists agree on the general configuration of Pangea • well-constrained by the seafloor magnetic anomaly data • oldest anomalies in NW Pacific ~160 Ma

25. Age of the ocean floor (Mueller et al., 1996)

26. Pangea • most scientists agree on the general configuration of Pangea • well-constrained by the seafloor magnetic anomaly data • oldest anomalies in NW Pacific ~160 Ma • actually positions between continents always being ‘tweaked’ • ‘rigid’ vs. ‘non-rigid’ plates

27. Who’s using plate tectonics? • paleontologists • other geologists/scientists trying to put their data into a geologic timeframe • oil/mineral exploration • Where (i.e., at what latitude) was the plate at xx time? • What were its conjugate plates? • Middle/high school students

28. The PLATES ProjectWhat type of research do we do and how do we do it? • Refinement of our plate models • Breaking up the major plates into smaller elements as a means of dealing with the non-rigidity of plates • Extension of our plate model ever further into the past

29. Data • Seafloor-spreading data (anomalies/fracture zones) • Free-air gravity data (constrains fracture zones, shelf edges, other features) • Hotspot data/tracks, large igneous provinces • Paleomagnetic data • Onshore geologic data

33. Closure of the South Atlantic (Lawver et al. 1998). Blue lines are shelf edges that are closely matched. Red lines indicate where South America and Africa were broken into smaller elements (for non-rigid plate tectonics).

34. Tight-fit of Pangea (Lawver et al. 1998)

35. Tools • Interactive plate reconstruction software • Plotting software (both in-house & GMT)

36. References (incomplete)Bullard, E., Everett, J.E., and Gilbert Smith, A., 1965, The fit of the continents around the Atlantic, in P.M.S. Blackett, E. Bullard and S.K. Runcorn (eds.), A symposium on continental drift, 1088: 41-51, Royal Society of London, Phil. Trans.Cox, A., 1973, Plate Tectonics and Geomagnetic Reversals, W.H. Freeman and Company, San Francisco, p. 702. – Has reprints of key papers.Dietz, R.S., 1961, Continent and ocean basin evolution by spreading of the sea floor, Nature, 190:854-857.Ewing, M., and Heezen, B.C., 1956, Some problems of Antarctic submarine geology, in A. Crary, L.M. Gould, E.O. Hurlburt, H. Odishaw and W.E. Smith (eds.), Antarctica in the International Geophysical year, Monograph, 1: 75-81, American Geophysical Union.Hess, H. H., 1962, History of ocean basins, in Engel, A.E.J., James, H.L., and Leonard, B.F. (eds.), Petrologic studies: A volume in Honor of A.F. buddington, Geological Society of America, p. 599-620.Irving, E., 1956, Palaeomagnetic and palaeoclimatological aspects of polar wandering, Pure and Applied Geophysics, 33:23-41.Lawver, L.A., Gahagan, L.M., and Dalziel, I.W.D., 1998, A Tight fit-Early Mesozoic Gondwana, A Plate Reconstruction Perspective, in Y. Motoyoshi and K. Shiraishi (eds.), Origin and Evolution of Continents: Proceedings of the International Symposium "Origin and Evolution of Continents," 13-14 October, 1997, Tokyo, Memoirs, 214-229, National Institute of Polar Research

37. LePichon, X., 1968, Sea-floor spreading and continental drift, Journal of Geophysical Research, 73:3661-3697.McKenzie, D.P., and Parker, D.L., 1967, The North Pacific: An example of tectonics on a sphere, Nature, 216:1276-1280.Menard, H.W., and Dietz, R.S., 1952, Mendocino submarine escarpment, Journal of Geology, 60:266-278.Morgan, W.J., 1968, Rises, trenches, great faults, and crustal blocks, Journal of Geophysical Research, 73:1959-1982.Runcorn, S.K., 1956, Palaeomagnetic comparisons between Europe and North America, Geological Association of Canada, Proceedings, 8:77-85.Vine and Matthews (1963) – magnetic stripes of the ocean sea floor are created by the magnetization of oceanic crust as it is formed at the mid-ocean ridges. The older crust moves away from the ridge as new crust forms.Wegener, A., 1912, Die Entstehung der Kontinente, Geol. Rundschau, v. 3, 276-292.Wilson, J.T., 1965, A new class of faults and their bearing on continental drift, Nature, 207:343-347.