observations related to plate tectonics • ocean and continent
TRANSCRIPT
![Page 1: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/1.jpg)
Observations Related to Plate Tectonics
David T. SandwellScripps Inst. Of Oceanography"
• Ocean and continent topography, hypsometry, and crustal thickness.
• Global seismicity, Benioff zones, and focal mechanisms
• Global volcanic activity
• Geoid Height and gravity anomaly
• Marine magnetic anomalies
![Page 2: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/2.jpg)
plate tectonics"
(Trujillo A. P. and H. V. Thurman, Essentials of Oceanography, Prentice Hall, New Jersey, 2004)
![Page 3: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/3.jpg)
What were they smoking in the 60’s?"
(Holden, J. C. and P. R. Vogt, Graphic Solutions to Problems of Plumacy, EOS Trans. AGU, 56, 573-560, 1977)
![Page 4: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/4.jpg)
Why wasn’t plate tectonics discovered until the 60’s?
Geologists examined continental rocks. Geodesists made maps of shorelines and mountains. Paleontologists studied the 500 million-year old fossil record in
sedimentary rocks. Glaciologists found evidence for glaciers at low latitudes.
Evidence from the continents is indirect Continental drift theory plate tectonic theory
≠
![Page 5: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/5.jpg)
Why wasn’t plate tectonics discovered until the 60’s?
seafloor bathymetry - ridges, fracture zones, trenches
seafloor and backarc volcanism
seismicity and focal mechanisms
marine magnetic anomalies
- Plate Tectonic evidence mainly from seafloor
- Need ships, echo sounders, magnetometers, seismometers mostly developed after WW2 and during the Cold War.
![Page 6: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/6.jpg)
[Smith and Sandwell, 1997] Google Earth version at http://topex.ucsd.edu or ftp://topex.ucsd.edu/pub/srtm30_plus/SRTM30_PLUS.kmz
![Page 7: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/7.jpg)
hypometric curve
![Page 8: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/8.jpg)
EXERCISE: The median seaflooor depth is ~4 km and the median ocean crustal thickness is ~6 km. The most likely elevation of the continent is 0 km. Assume oceanic and continental crust have the same density. How thick is the continental crust?
![Page 9: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/9.jpg)
[Laske et al., 2000]
![Page 10: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/10.jpg)
![Page 11: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/11.jpg)
active and passive margins
(The Ocean Basins, Open University)
![Page 12: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/12.jpg)
Atlantic profile
(The Ocean Basins, Open University)
![Page 13: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/13.jpg)
fast vs. slow spreading"
![Page 14: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/14.jpg)
abyssal hills: fast v. slow spreading rate
[Smith, W.H.F.: personal communication]
![Page 15: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/15.jpg)
volcanoes and seamounts
(The Ocean Basins, Open University)
![Page 16: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/16.jpg)
global seamount distribution
[Wessel JGR, 2001]
![Page 17: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/17.jpg)
land volcanoes
![Page 18: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/18.jpg)
uncharted seamounts > 3 km tall
![Page 19: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/19.jpg)
size distribution of seamounts
[Wessel JGR, 2001]
![Page 20: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/20.jpg)
global seismicity
![Page 21: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/21.jpg)
[Hayes et al., JGR 2012]
![Page 22: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/22.jpg)
![Page 23: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/23.jpg)
stress and focal mechanisms"
topo"high
topo"flat
reverse fault topo"low
normal fault
strike-slip"fault
[Luttrell and Sandwell, submitted to JGR, 2011]
![Page 24: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/24.jpg)
global mid-ocean ridge "
• alternating spreading ridge and transform offset segments"
• ridge earthquakes have normal focal mechanism"
• transform earthquakes have strike-slip focal mechanism"
[Luttrell and Sandwell, submitted to JGR, 2011]
![Page 25: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/25.jpg)
constrain the magnitude of the regional tectonic stress"• calculate topographic stress for wavelength < 350 km"• add to this a regional horizontal stress field"• adjust 3 components of regional stress to match style of faulting"
[Luttrell and Sandwell, submitted to JGR, 2011]
![Page 26: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/26.jpg)
Kurile Subduction
Zone "[Ammon, Kanamori & Lay Nature 2008)]
Why are there both thrust and normal fault mechanisms at a subduction zone?
![Page 27: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/27.jpg)
geoid height
![Page 28: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/28.jpg)
ridges and transforms"
500
km
gravity from satellite altimetry Google Earth version at http://topex.ucsd.edu
![Page 29: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/29.jpg)
fracture zones"
![Page 30: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/30.jpg)
subduction zones"
![Page 31: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/31.jpg)
triple junction"
![Page 32: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/32.jpg)
back-arc spreading"
![Page 33: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/33.jpg)
magnetic reversals
![Page 34: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/34.jpg)
figure: modified from Pitman and Heirtzler, 1966. Science, 154, 1164-1171
![Page 35: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/35.jpg)
FZ direction + magnetic anomalies = seafloor age [Mueller et al., 1997]"
![Page 36: Observations Related to Plate Tectonics • Ocean and continent](https://reader031.vdocuments.net/reader031/viewer/2022022418/58a2dc911a28abbe5a8bda60/html5/thumbnails/36.jpg)
Observations Related to Plate Tectonics
David T. SandwellScripps Inst. Of Oceanography"
• Ocean and continent topography, hypsometry, and crustal thickness. • Global seismicity, Benioff zones, and focal mechanisms • Global volcanic activity • Geoid Height and gravity anomaly • Marine magnetic anomalies
Next class: • triple junction closure • plate motions on a sphere