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The Afar Triple Junction (also called the Afro-Arabian Rift System) is located along a divergent plate boundary dividing the Nubian, Somalian, and Arabian plates. This area is considered a present-day example of continental rifting leading to seafloor spreading and producing an oceanic basin. Here, the Red Sea Rift meets the Aden Ridge and the East African Rift. It extends a total of 6500 km in three arms from the Afar Depression to Mozambique. The connecting three arms form a triple junction. The northern most branching arm extends North through the Red Sea and into the Dead Sea, while the eastern arm extends through the Gulf of Aden and connects to the Mid-Indian Ocean ridge further to the east. Both of these rifting arms are below sea level and are similar to a mid-ocean ridge.〔 The third rifting arm runs south extending around 4000 km through the countries of Kenya, Uganda, the Democratic Republic of Congo, Rwanda, Burundi, Tanzania, Zambia, Malawi, and finally Mozambique. This southern rifting arm is better known as the East African Rift or the East African Rift System (EARS), when it includes the Afar Triangle. ==Doming and rifting== A rift is the result of pulling apart or extension of both the lithosphere and crust (note that the crust is a part of the lithosphere). This is a product of what is referred to as mantle upwelling where hotter asthenosphere rises up into colder lithosphere. This rise is associated with thinning and stretching of the lithosphere. Rifting is said to have begun in the Late Cretaceous epoch to 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 of the subduction in the north there was mantle upwelling causing the crust to down warp and swell into domes. There are many domes throughout the East African Rift System. The plume is thought to have begun under Lake Tana in Ethiopia.〔 The Kenyan dome has been studied extensively. Gani 2007 proposes that episodic increase of incision of the Ethiopian Plateau suggests episodic growth rates within the plateau. This is proposed since the incision rates have no correlation to the past climate events. Using Archimedes’ principle of isostatic rebound, 2.05 km uplift has occurred within the last 30 Ma. Using the environmental correlations and current topographic locations of the Jurassic Upper Limestone and Cretaceous Upper Sandstone, the net rock uplift of the Ethiopian Plateau would be 2.2 km since ca. 150 Ma. The thinned Ethiopian lithosphere could have resulted in ponding from mantle plume and subsequent uplift. Baker, B.H. 1972 also suggests 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 400 m uplift and the end of the Neogene with a staggering 1,500 m 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 500 m 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 1000 m in the Afar region. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Afar Triple Junction」の詳細全文を読む スポンサード リンク
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