The Red Sea Rift is a spreading center between two

tectonic plate Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

s, the

African Plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plate ...

and the

Arabian Plate The Arabian Plate is a minor tectonic plate in the Northern and Eastern Hemispheres. It is one of the three continental plates (along with the African and the Indian Plates) that have been moving northward in geological history and colliding ...

. It extends from the Dead Sea Transform fault system, and ends at an intersection with the

Aden Ridge The Aden Ridge is a part of an active oblique rift system located in the Gulf of Aden, between Somalia and the Arabian Peninsula to the north. The rift system marks the divergent boundary between the Somali and Arabian tectonic plates, extending ...

and the

East African Rift The East African Rift (EAR) or East African Rift System (EARS) is an active continental rift zone in East Africa. The EAR began developing around the onset of the Miocene, 22–25 million years ago. In the past it was considered to be part of ...

, forming the

Afar Triple Junction The Afar Triple Junction (also called the Afro-Arabian Rift System) is located along a divergent plate boundary dividing the Nubian, Somali, and Arabian plates. This area is considered a present-day example of continental rifting leading to s ...

in the

Afar Depression The Afar Triangle (also called the Afar Depression) is a geological depression caused by the Afar Triple Junction, which is part of the Great Rift Valley in East Africa. The region has disclosed fossil specimens of the very earliest hominins; ...

of the

Horn of Africa The Horn of Africa (HoA), also known as the Somali Peninsula, is a large peninsula and geopolitical region in East Africa.Robert Stock, ''Africa South of the Sahara, Second Edition: A Geographical Interpretation'', (The Guilford Press; 2004 ...

. The Red Sea Rift was formed by the divergence between the African Plate and the Arabian Plate. The rift transitioned from a continental rift to an oceanic rift. Magnetic anomalies suggest that the spreading rate on either side of the Red Sea is about 1 cm/year. The African plate has a rotation rate of 0.9270 degrees/ Ma, while the Arabian plate has a rotation rate of 1.1616 degrees/Ma.

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

Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', ...

, followed by major seafloor spreading in the late Eocene and early

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but t ...

. This was followed by a period of 30 Ma of no motion, during which a large amount of 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.

Mechanism of rifting

A three-step process 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 Delamination is a mode of failure where a material fractures into layers. A variety of materials including laminate composites and concrete can fail by delamination. Processing can create layers in materials such as steel formed by rolling a ...

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 upper mantle. All geophysical data from the axial trough reveal seismic velocities typical for oceanic crust. The main trough, however, is characterized by a high degree of lateral variation, with abrupt changes in

basement A basement or cellar is one or more Storey, floors of a building that are completely or partly below the storey, ground floor. It generally is used as a utility space for a building, where such items as the Furnace (house heating), furnace, ...

velocities from typical continental to typical oceanic signatures.

Volcanic activity

The rift zone includes the island of Jabal al-Tair, formed by the basaltic stratovolcano of the same name, located northwest of the Bab al-Mandab passage at the mouth of the

Red Sea The Red Sea ( ar, البحر الأحمر - بحر القلزم, translit=Modern: al-Baḥr al-ʾAḥmar, Medieval: Baḥr al-Qulzum; or ; Coptic: ⲫⲓⲟⲙ ⲛ̀ϩⲁϩ ''Phiom Enhah'' or ⲫⲓⲟⲙ ⲛ̀ϣⲁⲣⲓ ''Phiom ǹšari''; ...

, about halfway between

Yemen Yemen (; ar, ٱلْيَمَن, al-Yaman), officially the Republic of Yemen,, ) is a country in Western Asia. It is situated on the southern end of the Arabian Peninsula, and borders Saudi Arabia to the north and Oman to the northeast and ...

and

Eritrea Eritrea ( ; ti, ኤርትራ, Ertra, ; ar, إرتريا, ʾIritriyā), officially the State of Eritrea, is a country in the Horn of Africa region of Eastern Africa, with its capital and largest city at Asmara. It is bordered by Ethiopi ...

. The volcano erupted on 30 September 2007, after 124 years of

dormancy Dormancy is a period in an organism's life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolic activity and therefore helps an organism to conserve energy. Dormancy tends to be c ...

Resources

The axial deep of the rift was the location of the first known hot hydrothermal brines discovered on the sea floor. Workers from 1949 through the 1960s confirmed the presence of hot () saline brines and associated metalliferous muds. The hot solutions were emanating from an active subseafloor rift.

References