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Darfur Dome
Darfur Dome or Darfur Volcanic Province is an area of about 100x400 km in Western Sudan. As well as its best-known and central feature, Deriba Crater, it encompasses the surrounding Marra Mountains (Jebel Marra) and Tagabo Hills, both formed around 16–10 Ma., and the Meidob Hills, formed around 6.8 Ma. There are currently two competing theories concerning Darfur Dome’s formation. The conventional view is that magmatism is the product of a rising mantle plume, with active volcanism being triggered by stress resolution along the Central African Fault Zone. Evidence for a plume origin includes domal uplift, gravity anomalies, and low seismic velocity zones in the mantle, though there is disagreement over whether these indicate a discreet, narrow plume under the Darfur region or a broad superplume with conduits feeding several African hotspots. Recently, some scientists have argued for a tectonic origin in which lithospheric extension, asthenospheric shear, and small-scale ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lithosphere
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time scales of up to thousands of years or more. The crust and upper mantle (Earth), upper mantle are distinguished on the basis of chemistry and mineralogy. Earth's lithosphere Earth's lithosphere, which constitutes the hard and rigid outer vertical layer of the Earth, includes the crust and the uppermost mantle. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, and deeper part of the upper mantle. The lithosphere–asthenosphere boundary is defined by a difference in response to stress. The lithosphere remains rigid for very long periods of geologic time in which it deforms elastically and through brittle failure, while the asthenosphere deforms viscously and accommodates strain through plasticity (physics), pl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Darfur
Darfur ( ; ar, دار فور, Dār Fūr, lit=Realm of the Fur) is a region of western Sudan. ''Dār'' is an Arabic word meaning "home f – the region was named Dardaju ( ar, دار داجو, Dār Dājū, links=no) while ruled by the Daju, who migrated from Meroë , and it was renamed Dartunjur ( ar, دار تنجر, Dār Tunjur, links=no) when the Tunjur ruled the area. Darfur was an independent sultanate for several hundred yearsRichard Cockett Sudan: Darfur and the failure of an African state. 2010. Hobbs the Printers Ltd., Totten, Hampshire. until it was incorporated into Sudan by Anglo-Egyptian forces in 1916. As an administrative region, Darfur is divided into five federal states: Central Darfur, East Darfur, North Darfur, South Darfur and West Darfur. Because of the War in Darfur between Sudanese government forces and the indigenous population, the region has been in a state of humanitarian emergency and genocide since 2003. The factors include religious and ethn ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanoes Of Sudan ...
This is a list of active and extinct volcanoes in Sudan. References {{Global Volcanism Program Sudan Volcanoes A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Central African Shear Zone
The Central African Shear Zone (CASZ) (or Shear System) is a wrench fault system extending in an ENE direction from the Gulf of Guinea through Cameroon into Sudan. The structure is not well understood. , there was still no general agreement about how the individual shears along the lineament link up. Description The shear zone dates to at least 640 Ma (million years ago). Motion occurred along the zone during the break-up of Gondwanaland in the Jurassic and Cretaceous periods. Some of the faults in the zone were rejuvenated more than once before and during the opening of the South Atlantic in the Cretaceous period. It has been proposed that the Pernambuco fault in Brazil is a continuation of the shear zone to the west. In Cameroon, the CASZ cuts across the Adamawa uplift, a post-Cretaeous formation. The Benue Trough lies to the north, and the Foumban Shear Zone to the south. Volcanic activity has occurred along most of the length of the Cameroon line from 130 Ma to the present ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Isotopes Of Helium
Although there are nine known isotopes of helium (2He) ( standard atomic weight: ), only helium-3 () and helium-4 () are stable. All radioisotopes are short-lived, the longest-lived being with a half-life of . The least stable is , with a half-life of (), although it is possible that may have an even shorter half-life. In the Earth's atmosphere, the ratio of to is . However, the isotopic abundance of helium varies greatly depending on its origin. In the Local Interstellar Cloud, the proportion of to is , which is times higher than that of atmospheric helium. Rocks from the Earth's crust have isotope ratios varying by as much as a factor of ten; this is used in geology to investigate the origin of rocks and the composition of the Earth's mantle. The different formation processes of the two stable isotopes of helium produce the differing isotope abundances. Equal mixtures of liquid and below separate into two immiscible phases due to differences in quantum statistics: ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
S Wave
__NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because they move through the body of an object, unlike surface waves. S waves are transverse waves, meaning that the direction of particle motion of a S wave is perpendicular to the direction of wave propagation, and the main restoring force comes from shear stress. Therefore, S waves cannot propagate in liquids with zero (or very low) viscosity; however, they may propagate in liquids with high viscosity. The name ''secondary wave'' comes from the fact that they are the second type of wave to be detected by an earthquake seismograph, after the compressional primary wave, or P wave, because S waves travel more slowly in solids. Unlike P waves, S waves cannot travel through the molten outer core of the Earth, and this causes a shadow zone for S ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mantle Convection
Mantle convection is the very slow creeping motion of Earth's solid silicate mantle as convection currents carrying heat from the interior to the planet's surface. The Earth's surface lithosphere rides atop the asthenosphere and the two form the components of the upper mantle. The lithosphere is divided into a number of tectonic plates that are continuously being created or consumed at plate boundaries. Accretion occurs as mantle is added to the growing edges of a plate, associated with seafloor spreading. Upwelling beneath the spreading centers is the rising component of mantle convection. The hot material added at spreading centers cools down by conduction and convection of heat as it moves away from the spreading centers. At the consumption edges of the plate, the material has thermally contracted to become dense, and it sinks under its own weight in the process of subduction usually at an ocean trench. Subduction is the descending component of mantle convection. This sub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Shear (geology)
Boudinaged quartz vein (with strain fringe) showing ''Fault (geology)">sinistral shear sense'', Starlight Pit, Fortnum Gold Mine, Western Australia In geology, shear is the response of a rock to deformation usually by compressive stress and forms particular textures. Shear can be homogeneous or non-homogeneous, and may be pure shear or simple shear. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics. The process of shearing occurs within brittle, brittle-ductile, and ductile rocks. Within purely brittle rocks, compressive stress results in fracturing and simple faulting. Rocks Rocks typical of shear zones include mylonite, cataclasite, S-tectonite and L-tectonite, pseudotachylite, certain breccias and highly foliated versions of the wall rocks. Shear zone A shear zone is a tabular to sheetlike, planar or curviplanar zone composed of rocks that are more highly strained than rocks adjacent to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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 ~ below the surface, and extends as deep as . However, the lower boundary of the asthenosphere is not well defined. The asthenosphere is almost solid, but a slight amount of melting (less than 0.1% of the rock) contributes to its mechanical weakness. More extensive decompression melting of the asthenosphere takes place where it wells upwards, and this is the most important source of magma on Earth. It is the source of mid-ocean ridge basalt (MORB) and of some magmas that erupted above subduction zones or in regions of continental rifting. Characteristics The asthenosphere is a part of the upper mantle just below the lithosphere that is involved in plate tectonic movement and isostatic adjustments. It is composed of peridotite, a rock containing mostly the minerals olivine and pyroxene. The lithosphere-asthenosphere boundary is con ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Plate Theory (volcanism)
The plate theory is a model of volcanism that attributes all volcanic activity on Earth, even that which appears superficially to be anomalous, to the operation of plate tectonics. According to the plate theory, the principal cause of volcanism is extension of the lithosphere. Extension of the lithosphere is a function of the lithospheric stress field. The global distribution of volcanic activity at a given time reflects the contemporaneous lithospheric stress field, and changes in the spatial and temporal distribution of volcanoes reflect changes in the stress field. The main factors governing the evolution of the stress field are: # Changes in the configuration of plate boundaries. # Vertical motions. # Thermal contraction. Lithospheric extension enables pre-existing melt in the crust and mantle to escape to the surface. If extension is severe and thins the lithosphere to the extent that the asthenosphere rises, then additional melt is produced by decompression upwelling. Or ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Deriba (caldera)
Deriba is a Pleistocene or Holocene caldera in Darfur, Sudan. Part of the volcanoes of the Marra Mountains, it lies on the Darfur dome and like the Tagabo Hills and Meidob Hills volcanism may be the product of a mantle plume. After the separation of South Sudan, the highest point of Sudan is on the margin of the caldera. The caldera lies atop a shield volcano or ash cone in the southern Marra Mountains, which developed first as a pile of basaltic lava flows and later as layers of volcanic ash and tuff, including the eruptions that formed the caldera. A large eruption occurred about 3,520 ± 100 years before present, and hot springs and fumaroles are active to the present day. Deriba contains two lakes, one in the northeastern side of the main caldera and the other in a cone in the southwestern sector of the Deriba caldera. The fresher southwestern lake is smaller but considerably deeper than the saltier northeastern lake; in the late Pleistocene the caldera was filled with a la ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
