Red Sea Rift

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Red Sea Rift between the African (Nubian) Plate and the Arabian plate

The Red Sea Rift is a

Afar Depression of the Horn of Africa
.

The Red Sea Rift was formed by the divergence between the African and Arabian plates. The rift transitioned from a

Ma (million years), while the Arabian plate has a rotation rate of 1.1616 degrees/Ma.[2]

Spreading model

A two-stage spreading model explains the tectonic evolution in this region. The first major rift motion was seen in the lower/middle

evaporites were deposited. After this quiet period of deposition, a new period of activity started about five million years ago. This new phase of spreading caused considerable disturbance to the sediments that were deposited, which created an unstable situation as the crust and sediments parted and the axial trough evolved. Normal faulting along the rift valley during earthquakes shows that the extensional motion is continuing.[3]

Mechanism of rifting

A three-step process[4] has been proposed for the mechanism of rifting.

First, a thermal anomaly developed in the mantle in the earliest stages of rifting, causing the rise of the asthenosphere and the thinning of the subcrustal continental lithosphere. There have been several mechanisms proposed to achieve this, such as convective thermal thinning.

This was followed by

decompressions, which occurred due to uplift related to the gradual stretching and thinning of the crust as rifting continued. Stretching and thinning can take place either according to a symmetrical, pure shear, extension model, or due to an asymmetric, detachment-delamination model. Basaltic dykes
are also injected during the stretching and thinning.

As the basaltic injections become restricted to a narrow axial zone, true seafloor spreading initiates with the Vine-Matthews-type magnetic anomaly stripes. Axial propagation of the oceanic rift occurs, resulting in a continuous axis of spreading. The rift may be intersected by a shear or fracture zone, which act as locked zones and prevent further propagation. Zones of compression may develop.

Composition

While there is a general agreement that the axial trough of the Red Sea originated by seafloor spreading, and therefore is underlain by oceanic crust, the nature of the crust beneath the main trough and coastal plains of the Red Sea is still controversial, leading to the development of a few theories. One theory suggests that the entire Red Sea basin is underlain by oceanic crust, while another theory claims that the main trough is underlain only in part by oceanic crust. A third theory suggests that outside the axial trough, the crust has a continental composition, with the presence of basaltic dykes, while another hypothesis suggests that the lower crust in the rift consists of rift meta-sediments, in direct contact with the

seismic velocities typical for oceanic crust. The main trough, however, is characterized by a high degree of lateral variation, with abrupt changes in basement velocities from typical continental to typical oceanic signatures.[5]

Volcanic activity

The rift zone includes the island of

dormancy
.

Resources

The axial deep of the rift was the location of the first known hot

rift.[6]

See also

References

  1. doi:10.1029/jb094ib02p01677
    .
  2. doi:10.1038/226243a0
    .
  3. doi:10.1038/247007a0
    .
  4. doi:10.1130/0016-7606(1994)106<1474:geotsr>2.3.co;2
    .
  5. doi:10.1029/jb092ib12p12803
    .
  6. ISBN 978-3-662-28603-6
    .
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