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Rifting and Extensionnal Tectonics

Earth 238-25. Rifting and Extensionnal Tectonics. *Tectonic extension : crustal scale extension in the horizontal plane (parallel to the surface of earth). Crustal thinning *Extension in general: (stretching, elongation). Increase in lenght of a line or a distance between two points.

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Rifting and Extensionnal Tectonics

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  1. Earth 238-25 Rifting and Extensionnal Tectonics *Tectonic extension : crustal scale extension in the horizontal plane (parallel to the surface of earth). Crustal thinning *Extension in general: (stretching, elongation). Increase in lenght of a line or a distance between two points. Elongation: e= (l-l0)/l0 Extension or Stretching s= l/ l0= 1+e http://www.uib.no/people/nglhe/Extension.swf

  2. Earth 238-25 Normal faults

  3. Earth 238-25 Geometry Pure shear rifting Simple shear rifting

  4. Earth 238-25 Geometry *C structures Low relief accomodation zone High relief accomodation zone

  5. Earth 238-25 Rifting and Extensionnal Tectonics *TectonicEnvironments: -Continental Margin Slope Failures, Gulf of Mexico, also landslides -Continental Rifts: North Africa -Rifted continental margins: Continental margins around Atlantic for example -Compressional tectonic setting: metamorphic core complex

  6. Earth 238-25 Continental Margin Slope Failures *landslides *Continental Margin Slope Failures

  7. Earth 238-25 Rifting *Why rifts form: -Upwelling of hot mantle material -Change in plate geometry -Extension and reactivation of weakness zones (ancient rifts, orogenic Suture zones)

  8. Earth 238-25 Rifting *Change in plate geometry

  9. Earth 238-25 Continental rift

  10. Earth 238-25 Rifting

  11. Earth 238-25 Rifting

  12. Earth 238-25 Rifting

  13. Earth 238-25 Rifting

  14. Earth 238-25 Rifting Kilimandjaro volcano: 5895 m

  15. Earth 238-25 Rifting *Passive margin

  16. Earth 238-25 Rifting

  17. Earth 238-25 Rifting *From continental rifting to ocean:

  18. Earth 238-25 Rifting

  19. Earth 238-25 Rifting

  20. Earth 238-25 Rifting

  21. Earth 238-25 Rifting *Tansform faults:

  22. Earth 238-25 Rifting Fast-spreading ridges like the northern and southern East Pacific Rise have smoother topography at the ridge crest and look more like domes. They have relief of only a few hundred meters down the sides of the ridge to the crest. They have valleys at the crest of the ridge but usually they are much smaller. Sometimes these small valleys, or troughs, are less than 100 m wide and only 10-20 meters deep. Slow spreading ridges like the Mid-Atlantic Ridge generally have large, wide rift valleys, sometimes as big as 10-20 km wide and very rugged terrain at the ridge crest that can have relief of up to a thousand meters

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