Rifting and Extensionnal TectonicsEarth 238-25

*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

Normal faultsEarth 238-25

GeometryEarth 238-25

Pure shear rifting

Simple shear rifting

GeometryEarth 238-25

High relief accomodationzone

Low relief accomodationzone

*C structures

Rifting and Extensionnal TectonicsEarth 238-25

*Tectonic Environments:

-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

Continental Margin Slope FailuresEarth 238-25

*landslides

*Continental Margin Slope Failures

RiftingEarth 238-25

*Why rifts form:

-Upwelling of hot mantle material

-Change in plate geometry

-Extension and reactivation of weakness zones (ancient rifts, orogenicSuture zones)

RiftingEarth 238-25

*Change in plate geometry

Continental riftEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

Kilimandjaro volcano: 5895 m

RiftingEarth 238-25

*Passive margin

RiftingEarth 238-25

RiftingEarth 238-25

*From continental rifting to ocean:

RiftingEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

RiftingEarth 238-25

*Tansform faults:

RiftingEarth 238-25

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

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.