A
rift is the result of pulling apart or extension of
lithosphere, including the
crust, caused by mantle upwelling where hotter
asthenosphere magma rises up into the colder lithosphere to stretch and thin it. The triple rift is thought to have begun in the
Late Cretaceous epoch to the Paleogene period. At that time the African plate was experiencing far-field stresses caused by portions of the northern boundary of the African plate subducting under the Eurasian plate. Today, the Arabian plate is experiencing a crustal down pull, or
slab pull, that has separated from the African plate. At the same time as the
subduction in the north, there was mantle upwelling causing the crust to down warp and swell into
domes throughout the East African Rift System. The Kenyan dome has been studied extensively. The plume is thought to have begun under
Lake Tana in
Ethiopia. Baker et al. (1972) also suggest that the uplift of this area is sporadic and divided by long periods of stability and erosion. Some periods of uplift are recorded at the end of the Cretaceous that resulted in of uplift and the end of the Neogene with a staggering in magnitude. The Ethiopian dome experienced its largest uplift coinciding with the end of the Neogene uplift associated with the Kenyan dome. It has been argued that the current Ethiopian plateau is a result of the most recent uplift of estimated to be an Oligocene–early Miocene event. But the most accepted argument of the plateau is the result of the
Paleogene flood-basalts. The uplift associated with both domes has resulted in major structural features due to the swelling and warped crustal extension. The two areas of swelling resulted in a large
depression between the two
domes and subsidence along the coastal regions. The uplift caused by the Ethiopian dome resulted in a massive faulting area of in the Afar region.
East African Rift The
East African Rift is an active rift between the Nubian and Somali protoplates. This rift is caused by elevated heat flow from the mantle under
Kenya and the Afar region. Trending NNE to SSW, the East African Rift is composed of a western and an eastern branch. The eastern branch (sometimes called the
Gregory Rift) is characterized by high
volcanic activity and the western branch (sometimes called the
Albertine Rift) is characterized by deeper
basins, which contain lakes and sediments. The lakes in this area (e.g. Lake Tanganyika and Lake Rukwa) are located in highly rifted basins and have an inter-fingering relationship with faults. Many of the lakes are bounded by normal or strike-slip faults.
Red Sea Rift in the background The
Red Sea Rift is between the African (or Nubian) and Arabian plates. The rift runs along the length of the Red Sea, starting from the
Dead Sea to the Afar triple junction. Within the rift, in the Red Sea, there are many volcanoes, including the
Jabal al-Tair. The extension rate for this rift varies from about .
Aden Ridge The
Aden Ridge is a divergent plate boundary that divides the African (or Somali) and Arabian plate. It extends from the triple junction eastward to the
Owen fracture zone, where it meets the Aden–Owen–Carlsberg triple junction between the African, Arabian, and
Indo-Australian plates. The spreading rate for Aden Ridge is about near the Afar triple junction.
Afar Depression Before the initial rifting began, Africa was one plate, but as rifting proceeded the plate it began to tear into the Arabian, Somali, and Nubian plates (with the Nubian still sometimes called the African plate). According to McKenzie and Morgan's 1969 classification, the Afar triple junction is of ridge-ridge-ridge (RRR) type, describing the movement of the three plates with respect to each other. The Arabian, Somali, and Nubian plates are all
divergent margins with respect to the adjacent plates. Following Mackenzie and Morgan's stability model, RRR geometry will continue stably through time until there is a change in the tectonic movement. The
Afar Depression is a geological depression that ranges in height from The area has experienced many domal uplifts, including the Afar dome beginning 40 Mya. This uplift caused massive crustal extension leading to horst and graben structures associated with normal, extensional, faults. The uplift ended in collapse around 25 Mya into the Afar depression covering more than and spreading at a rate of . ==Implications of volcanism==