The Red Sea Rift is a

mid-ocean ridge A mid-ocean ridge (MOR) is a undersea mountain range, seafloor mountain system formed by plate tectonics. It typically has a depth of about and rises about above the deepest portion of an ocean basin. This feature is where seafloor spreading ...

between two

tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

s, the African plate and the Arabian plate. It extends from the

Dead Sea Transform The Dead Sea Transform (DST) fault system, also sometimes referred to as the Dead Sea Rift, is a series of Fault (geology), faults that run for about 1,000 km from the Marash triple junction (a junction with the East Anatolian Fault in south ...

fault system, and ends at an intersection with the Aden Ridge 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. It was formerly considered to be part of a l ...

, forming the Afar triple junction in the Afar Depression 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 and Arabian plates. 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 (million years), 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 ( ) is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene'' comes ...

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

Oligocene The Oligocene ( ) is a geologic epoch (geology), epoch of the Paleogene Geologic time scale, Period that extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that defin ...

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

evaporites An evaporite () is a water-soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...

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 The asthenosphere () is the mechanically weak and ductile region of the upper mantle of Earth. It lies below the lithosphere, at a depth between c. below the surface, and extends as deep as . However, the lower boundary of the asthenosphere i ...

and the thinning of the subcrustal continental

lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...

. 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

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...

. 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 is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

velocities from typical continental to typical oceanic signatures.

Volcanic activity

The rift zone includes the island of

Jabal al-Tair Jabal al-Tair Island (or Jebel Teir, Jabal al-Tayr, Tair Island, Al-Tair Island, Jazirat at-Tair) ( ''Jazīrat Jabal aṭ-Ṭayr'', 'Bird Mountain Island') is a roughly oval volcano, volcanic island in Yemen, northwest of the constricted Bab al-M ...

, 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 is a sea inlet of the Indian Ocean, lying between Africa and Asia. Its connection to the ocean is in the south, through the Bab-el-Mandeb Strait and the Gulf of Aden. To its north lie the Sinai Peninsula, the Gulf of Aqaba, and th ...

, about halfway between

Yemen Yemen, officially the Republic of Yemen, is a country in West Asia. Located in South Arabia, southern Arabia, it borders Saudi Arabia to Saudi Arabia–Yemen border, the north, Oman to Oman–Yemen border, the northeast, the south-eastern part ...

and

Eritrea Eritrea, officially the State of Eritrea, is a country in the Horn of Africa region of East Africa, with its capital and largest city being Asmara. It is bordered by Ethiopia in the Eritrea–Ethiopia border, south, Sudan in the west, and Dj ...

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

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

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 In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

References

{{Major African geological formations

Rift In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...