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Plate Tectonics
By L.M. Gahagan
Rough draft
October 5, 2001
Historical Aspects
(From Cox, 1973)
Key events
1.
mapping of seafloor topography
(presence of guyots, mid-ocean ridges, etc.)
Seafloor topography (Smith and Sandwell 1997)
Historical Aspects
(From Cox, 1973)
Key events
1.
2.
mapping of seafloor topography
measuring the seafloor’s magnetic field
(‘magnetic stripes’)
ridge
Magnetic ‘stripes’ along the Reykjanes Ridge. From Vine 1966
Historical Aspects
(From Cox, 1973)
Key events
1.
2.
3.
mapping of seafloor topography
measuring the seafloor’s magnetic field
timing the north-south flips of earth’s magnetic field
(paleomagnetism)
Historical Aspects
(From Cox, 1973)
Key events
1.
2.
3.
4.
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)
Earthquake epicenters (Engdahl et al. 1998) and Holocene volcanoes (Smithsonian Global Volcanism Project)
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.
ridge
Magnetic ‘stripes’ along the Reykjanes Ridge. From Vine 1966
synthetic wiggle
‘picks’
chron
Interpretation of marine magnetic anomalies. From Barckhausen et al. 2001
.
Inpretation of magnetic anomalies from shiptrack wiggles, (Barckhausen et al. 2001).
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
Division of earth into plates (Wilson 1965).
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
Use of Euler poles to rotate plates on a sphere (Morgan, 1968).
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
Major plates as mapped by Morgan (1968)
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
Plate Tectonics Today
explains many geologic phenomena
- volcanic/earthquake activity
- trenches, mid-ocean ridges
- hotspot tracks
- similarity between fossils & geologic rock
assemblages across oceans
Pangea
o
most scientists agree on the general configuration of Pangea
Pangea
o
o
o
most scientists agree on the general configuration of Pangea
well-constrained by the seafloor magnetic anomaly data
oldest anomalies in NW Pacific ~160 Ma
Age of the ocean floor (Mueller et al., 1996)
Pangea
o
o
o
o
o
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
Who’s using plate tectonics?
o
o
o
paleontologists
other geologists/scientists trying to put their data into a geologic timeframe
oil/mineral exploration
o
o
•
Where (i.e., at what latitude) was the plate at xx time?
What were its conjugate plates?
Middle/high school students
The PLATES Project
What type of research do we do and
how do we do it?
o Refinement of our plate models
o 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
Data
o Seafloor-spreading data (anomalies/fracture
zones)
o Free-air gravity data (constrains fracture
zones, shelf edges, other features)
o Hotspot data/tracks, large igneous provinces
o Paleomagnetic data
• Onshore geologic data
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).
Tight-fit of Pangea (Lawver et al. 1998)
Tools
o Interactive plate reconstruction software
• Plotting software (both in-house & GMT)
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
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.