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 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 6,500 kilometers (4,000 mi) in three arms from the Afar Triangle 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.
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 million years.
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 Mya. 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 1,000 m in the Afar region.
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. The extension rate for this rift starts at about 6 millimeters per year in the north, and declines to the south.
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 7 to 17 millimeters per year.
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. The Aden Ridge is also a part of another triple junction in the Indian Ocean to the east, called the Aden-Owen-Carlsberg triple junction, which include the African, Arabian, and Indo-Australian plates. The spreading rate for Aden Ridge is about 17 millimeters per year near the Afar Triple Junction.
Before the initial rifting began, Africa was one plate but as rifting proceeded the plate began to tear in three directions. The rifting propagated along three branches that have now formed three separate plates: the Arabian, Somali, and the Nubian (also mentioned as the African plate). In 1969 McKenzie and Morgan published a paper and systematically explained types of triple junctions and their stability.
The Afar Triple Junction is known as a ridge-ridge-ridge or RRR triple junction. This describes the movement of the three plates with respect to each other. The Arabian, Somali, and Nubian plates are all divergent margins, or ridges, with respect to the adjacent plates. Following Mackenzie and Morgan's triple junction stability model, RRR geometry is stable and will continue through time until there is a change in the tectonic movement.
The Afar Depression is a geological depression that ranges in heights from 1,000 to −120 m (3,280 to −390 ft) This area, as mentioned above, experienced many domal uplifts. One of these uplifts was called the Afar dome. It began rising 40 Mya. This uplift caused massive crustal extension leading to horst and graben structures associated with normal, extensional, faults. The uplift of the Afar dome ultimately led to its collapse around 25 Mya. The Afar depression encompasses an area of more than 200,000 km2 and is spreading at a rate of 6 to 17 mm/yr.
There are many active volcanic areas centralized in the East African Rift System in comparison to the other areas in the Afro-Arabian rift system. Many protruding horsts show many layers of flood basalts. Using 40Ar/39Ar-isotope dating an age constraint can be implied on this basaltic series. It is found to be approximately 30 million years old. The trap series is dated to a time soon before the major rifting events began. Chorowicz, J. 2005 illustrated the trap series surrounding the newer Neogene volcanics. This helps quantify the amount of crustal extension and gives a model of pre-rifting crustal connection.
Seismic tomography compiles P-wave and S-wave data from movements within the earth to create a 3D velocity model of the Earth's subsurface. The models distinguish between fast velocity, high anomaly, and slow velocity, slow anomaly, time measurements.
Multiple tomography models show a slow anomaly structure beneath southern Africa. Grand, S. (1997) models the large anomaly to extend from the base of the mantle to approximately 1000 km depth. This slow anomaly is considered to be a plume upwelling.
Horsts and grabens are very well documented throughout this region. Although horsts and grabens do show and produce crustal extension, for a sufficient ocean basin to form, there needs to be extension that can accommodate for the extensive down fall of the grabens. Listric faults produce the correct model for this sufficient crustal extension. These faults have been documented by Chorowicz, J. 2005 and aid in further verification of the future of this region and the potential for continued extension and subsidence.
Past rifting events have been recorded in the geologic record and major rifting events have been seen to have an aulacogen with two successful rifting arms. Some geologists have proposed that the East African Rift System will be the aulacogen in the future but as of present-day there seems to be no aulacogen and the rifting in the EARS does not show any evidence of slowing its motion.
There is also the possibility to a subduction zone forming along the eastern most side of the continental Somali plate. This could be associated by the spreading of the Mid-Indian Oceanic ridge and the East African rift. To accommodate the compression of the Somali plate due to two extensional edges of the plate the oceanic plate might begin to subduct below the continental plate.
Evidence is showing that the East African Rift System is a classic continental-continental rifting event but the extent of research due to its age and continuing formation is diverse and filled with many hypothetical models that support and contrast each other. The rifting began in the Paleogene due to the far-field stress from the subduction of the Arabian plate under the Eurasian plate and the mantle upwelling that has been seen to move over time because of the multiple area of hot spots around the EARS.
This crustal uplift has created extension and horst and grabens and even listric faults which indicate a pre-oceanic basin structure. The future of this area is unknown. If current tectonics continue without change it is thought that an ocean basin with a mid-oceanic ridge will eventually separate the Nubian, Somali and Arabian plates.
The 1982 North Yemen earthquake hit near the city of Dhamar, North Yemen (now part of Yemen) on December 13. Measuring 6.2 on the moment magnitude scale, with a maximum perceived intensity of VIII (Severe) on the Mercalli intensity scale, as many as 2,800 people were killed and another 1,500 injured. The shock occurred within several hundred kilometers of a plate boundary in a geologically complex region that includes active volcanoes and seafloor spreading ridges. Yemen has a history of destructive earthquakes, though this was the first instrumentally recorded event to be detected on global seismograph networks.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 from the Owen Transform Fault in the Arabian Sea to the Afar Triple Junction or Afar Plume beneath the Gulf of Tadjoura in Djibouti.The Gulf of Aden is divided east to west into three distinct regions by large-scale discontinuities, the Socotra, Alula Fartak, and Shukra-El Shiek transform faults. Located in the central region, bounded by the Alula Fartak fault and Shukra-El Shiek fault, is the Aden spreading ridge. The Aden Ridge connects to the Sheba Ridge in the eastern region and to the Tadjoura Ridge in the western region. Due to oblique nature of the Aden Ridge, it is highly segmented. Along the ridge there are seven transform faults that offset it to the north.Afar Triangle
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, that is, the earliest of the human clade; and it is thought by some paleontologists to be the cradle of the evolution of humans, see Middle Awash, Hadar. The Depression overlaps the borders of Eritrea, Djibouti and the entire Afar Region of Ethiopia; and it contains the lowest point in Africa, Lake Asal, Djibouti, at 155 m (or 509 ft) below sea level.
The Awash River is the main waterflow into the region, but it runs dry during the annual dry season, and ends as a chain of saline lakes. The northern part of the Afar Depression is also known as the Danakil Depression. The lowlands are affected by heat, drought, and minimal air circulation, and contain the hottest places (year-round average temperatures) of anywhere on Earth.
The Afar Triangle is bordered as follows (see the topographic map): on the west by the Ethiopian Plateau and escarpment; to the north-east (between it and the Red Sea) by the Danakil block; to the south by the Somali Plateau and escarpment; and to the south-east by the Ali-Sabieh block (adjoining the Somali Plateau).Many important fossil localities exist in the Afar region, including the Middle Awash region and the sites of Hadar, Dikika, and Woranso-Mille. These sites have produced specimens of the earliest (fossil) hominins and of human tool culture, as well as many fossils of various flora and fauna.Basin and Range Province
The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins. The physiography of the province is the result of tectonic extension that began around 17 million years ago in the early Miocene epoch.
The numerous ranges within the province in the United States are collectively referred to as the "Great Basin Ranges", although many are not actually in the Great Basin. Major ranges include the Snake Range, the Panamint Range, the White Mountains, the Sandia Mountains, and the Tetons. The highest point fully within the province is White Mountain Peak in California, while the lowest point is the Badwater Basin in Death Valley at −282 feet (−86 m). The province's climate is arid, with numerous ecoregions. Most North American deserts are located within it.
Clarence Dutton famously compared the many narrow parallel mountain ranges that distinguish the unique topography of the Basin and Range to an "army of caterpillars marching toward Mexico." The Basin and Range Province should not be confused with The Great Basin, which is a sub-section of the greater Basin and Range physiographic region defined by its unique hydrological characteristics (internal drainage).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 a larger Great Rift Valley that extended north to Asia Minor.
The rift, a narrow zone, is a developing divergent tectonic plate boundary where the African Plate is in the process of splitting into two tectonic plates, called the Somali Plate and the Nubian Plate, at a rate of 6–7 mm (0.24–0.28 in) annually. As extension continues, lithospheric rupture will occur within 10 million years; the Somali Plate will break off and a new ocean basin will form.Gondwana
Gondwana ( ) or Gondwanaland was a supercontinent that existed from the Neoproterozoic (about 550 million years ago) until the Jurassic (about 180 million years ago).
It was formed by the accretion of several cratons. Eventually, Gondwana became the largest piece of continental crust of the Paleozoic Era, covering an area of about 100,000,000 km2 (39,000,000 sq mi). During the Carboniferous Period, it merged with Euramerica to form a larger supercontinent called Pangaea. Gondwana (and Pangaea) gradually broke up during the Mesozoic Era. The remnants of Gondwana make up about two thirds of today's continental area, including South America, Africa, Antarctica, Australia, Indian Subcontinent and Arabia.
The formation of Gondwana began c. 800 to 650 Ma with the East African Orogeny, the collision of India and Madagascar with East Africa, and was completed c. 600 to 530 Ma with the overlapping Brasiliano and Kuunga orogenies, the collision of South America with Africa and the addition of Australia and Antarctica, respectively.Great Rift Valley
The Great Rift Valley is a series of contiguous geographic trenches, approximately 6,000 kilometres (3,700 mi) in total length, that runs from the Beqaa Valley in Lebanon in Asia to Mozambique in southeastern Africa. While the name continues in some usages, it is rarely used in geology as it is considered an imprecise merging of separate though related rift and fault systems.
Today, the term is most often used to refer to the valley of the East African Rift, the divergent plate boundary which extends from the Afar Triple Junction southward across eastern Africa, and is in the process of splitting the African Plate into two new separate plates. Geologists generally refer to these incipient plates as the Nubian Plate and the Somali Plate.Great Rift Valley, Ethiopia
The Great Rift Valley of Ethiopia, (or Main Ethiopian Rift or Ethiopian Rift Valley) is a branch of the East African Rift that runs through Ethiopia in a southwest direction from the Afar Triple Junction. In the past, it was seen as part of a "Great Rift Valley" that ran from Mozambique to Syria.Gregory Rift
The Gregory Rift is the eastern branch of the East African Rift fracture system. The rift is being caused by the separation of the Somali plate from the Nubian plate, driven by a thermal plume. Although the term is sometimes used in the narrow sense of the Kenyan Rift, the larger definition of the Gregory Rift is the set of faults and grabens extending southward from the Gulf of Aden through Ethiopia and Kenya into Northern Tanzania, passing over the local uplifts of the Ethiopian and Kenyan domes.
Ancient fossils of early hominins, the ancestors of humans, have been found in the southern part of the Gregory Rift.Hotspot (geology)
In geology, the places known as hotspots or hot spots are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the surrounding mantle. Their position on the Earth's surface is independent of tectonic plate boundaries. There are two hypotheses that attempt to explain their origins. One suggests that hotspots are due to mantle plumes that rise as thermal diapirs from the core–mantle boundary. The other hypothesis is that lithospheric extension permits the passive rising of melt from shallow depths. This hypothesis considers the term "hotspot" to be a misnomer, asserting that the mantle source beneath them is, in fact, not anomalously hot at all. Well-known examples include the Hawaii, Iceland and Yellowstone hotspots.Jon Kalb
Jon Kalb August 17, 1941 (Houston, Texas) - October 27, 2017 (Austin, Texas) was a research geologist with the Vertebrate Paleontology Laboratory (Texas Memorial Museum), University of Texas at Austin. He received a pre-doctoral fellowship from the
Carnegie Geophysical Laboratory in 1968, a graduate fellowship from Johns Hopkins University in 1969, and a BSc from American University in 1970.Lake Abbe
Lake Abbe, also known as Lake Abhe Bad, is a salt lake, lying on the Ethiopia-Djibouti border. It is one of a chain of six connected lakes, which also includes (from north to south) lakes Gargori, Laitali, Gummare, Bario and Afambo. The river Awash flows into the no-drain lake. The Lake Abbe is the center of the Afar Depression. The Lac Abbe is considered one of the most inaccessible areas of the earth. The water itself is known for its flamingos. The scenery is unique.List of Northern Cordilleran volcanoes
The geography of northwestern British Columbia and Yukon, Canada is dominated by volcanoes of the Northern Cordilleran Volcanic Province formed due to continental rifting of the North American Plate. It is the most active volcanic region in Canada. Some of the volcanoes are notable for their eruptions, for instance, Tseax Cone for its catastrophic eruption estimated to have occurred in the 18th century which was responsible for the death of at least 2,000 Nisga'a people from poisonous volcanic gases, the Mount Edziza volcanic complex for at least 20 eruptions throughout the past 10,000 years, and The Volcano (also known as Lava Fork volcano) for the most recent eruption in Canada during 1904. The majority of volcanoes in the Northern Cordilleran Volcanic Province lie in Canada while a very small portion of the volcanic province lies in the U.S. state of Alaska.
Volcanoes of the Northern Cordilleran Volcanic Province are a part of the Pacific Ring of Fire. The largest and most persistent volcanoes are the Mount Edziza volcanic complex and Level Mountain in northwestern British Columbia which have had volcanic activity for millions of years. In the past 7.5 million years, the Mount Edziza volcanic complex has had five phases of volcanic activity while Level Mountain north of Edziza has had three phases of volcanic activity in the past 14.9 million years. The 1,000 km2 (390 sq mi) Mount Edziza volcanic complex has been made into a provincial park since 1972 to protect its volcanic landscape. The 102 Northern Cordilleran volcanoes in the list below are grouped into their political regions in north-south order.Mid-ocean ridge
A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics. It typically has a depth of ~ 2,600 meters (8,500 ft) and rises about two kilometers above the deepest portion of an ocean basin. This feature is where seafloor spreading takes place along a divergent plate boundary. The rate of seafloor spreading determines the morphology of the crest of the mid-ocean ridge and its width in an ocean basin. The production of new seafloor and oceanic lithosphere results from mantle upwelling in response to plate separation. The melt rises as magma at the linear weakness in the oceanic crust, and emerges as lava, creating new crust and lithosphere upon cooling. The Mid-Atlantic Ridge is a spreading center that bisects the North and South Atlantic basins; hence the origin of the name 'mid-ocean ridge'. Most oceanic spreading centers are not in the middle of their hosting ocean basis but regardless, are called mid-ocean ridges. Mid-ocean ridges around the globe are linked by plate tectonic boundaries and the outline of the ridges across the ocean floor appears similar to the seam of a baseball. The mid-ocean ridge system thus is the longest mountain range on Earth, reaching about 65,000 km (40,000 mi).Outline of plate tectonics
This is a list of articles related to plate tectonics and tectonic plates.Red Sea Rift
The Red Sea Rift is a spreading center between two tectonic plates, the African Plate and the Arabian Plate. It extends from the Dead Sea Transform fault system, and ends at an intersection with the Aden Ridge and the East African Rift, forming the Afar Triple Junction in the Afar Depression of the Horn of Africa.
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.Triple junction
A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of 3 types - a ridge (R), trench (T) or transform fault (F) - and triple junctions can be described according to the types of plate margin that meet at them (e.g. Transform-Transform-Trench, Ridge-Ridge-Ridge, or abbreviated F-F-T, R-R-R). Of the many possible types of triple junction only a few are stable through time ('stable' in this context means that the geometrical configuration of the triple junction will not change through geologic time). The meeting of 4 or more plates is also theoretically possible but junctions will only exist instantaneously.Volcanology of Canada
Volcanology of Canada includes lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds. It has a very complex volcanological history spanning from the Precambrian eon at least 3.11 billion years ago when this part of the North American continent began to form.Although the country's volcanic activity dates back to the Precambrian eon, volcanism continues to occur in Western and Northern Canada where it forms part of an encircling chain of volcanoes and frequent earthquakes around the Pacific Ocean called the Pacific Ring of Fire. But because volcanoes in Western and Northern Canada are in remote rugged areas and the level of volcanic activity is less frequent than with other volcanoes around the Pacific Ocean, Canada is commonly thought to occupy a gap in the Pacific Ring of Fire between the volcanoes of western United States to the south and the Aleutian volcanoes of Alaska to the north. However, the mountainous landscape of Western and Northern Canada includes more than 100 volcanoes that have been active during the past two million years and whose eruptions have claimed many lives. Volcanic activity has been responsible for many of Canada's geological and geographical features and mineralization, including the nucleus of North America called the Canadian Shield.
Volcanism has led to the formation of hundreds of volcanic areas and extensive lava formations across Canada, indicating volcanism played a major role in shaping its surface. The country's different volcano and lava types originate from different tectonic settings and types of volcanic eruptions, ranging from passive lava eruptions to violent explosive eruptions. Canada has a rich record of very large volumes of magmatic rock called large igneous provinces. They are represented by deep-level plumbing systems consisting of giant dike swarms, sill provinces and layered intrusions. The most capable large igneous provinces in Canada are Archean (3,800–2,500 million years ago) age greenstone belts containing a rare volcanic rock called komatiite.
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