|
Sonoma Orogeny
The Sonoma orogeny was a period of mountain building in western North America. The exact age and structure of the Sonoma orogeny is controversial. The orogeny is generally thought to have occurred during the Permian / Triassic transition, around 250 million years ago, following the Late Devonian Antler orogeny. The Sonoma orogeny was one of a sequence of accretionary events along the Cordilleran margin, possibly caused by the closure of the basin between the island arc of Sonomia and the North American continent. Evidence of this event has been reported throughout western North America, but most distinctly in northwest Nevada. The orogeny was named by Silberling and Roberts, who identified it with the Havallah Formation, originally thought to date to the Pennsylvanian and Permian ages but has since been revised to include rocks of Late Devonian and Mississippian age. Some geologists dispute whether convergent plate tectonics produced the Sonoma orogeny. Stratigraphy The Hava ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Permian
The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the region of Perm in Russia. The Permian witnessed the diversification of the two groups of amniotes, the synapsids and the sauropsids ( reptiles). The world at the time was dominated by the supercontinent Pangaea, which had formed due to the collision of Euramerica and Gondwana during the Carboniferous. Pangaea was surrounded by the superocean Panthalassa. The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior. Amniotes, which could better cope with these drier conditions, rose to dominance in place of their am ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial planet, rocky planet or natural satellite, moon. More than 90% of all volcanic rock on Earth is basalt. Rapid-cooling, fine-grained basalt is chemically equivalent to slow-cooling, coarse-grained gabbro. The eruption of basalt lava is observed by geologists at about 20 volcanoes per year. Basalt is also an important rock type on other planetary bodies in the Solar System. For example, the bulk of the plains of volcanism on Venus, Venus, which cover ~80% of the surface, are basaltic; the lunar mare, lunar maria are plains of flood-basaltic lava flows; and basalt is a common rock on the surface of Mars. Molten basalt lava has a low viscosity due to its relatively low silica content (between 45% and 52%), resulting in rapidly moving lava flo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oceanic Crust
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the rigid uppermost layer of the mantle. The crust and the rigid upper mantle layer together constitute oceanic lithosphere. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick; however, it is denser, having a mean density of about 3.0 grams per cubic centimeter as opposed to continental crust which has a density of about 2.7 grams per cubic centimeter. The crust uppermost is the result of the cooling of magma derived from mantle material below the plate. The magma is injected into the spreading center, which consists mainly of a partly solidified crystal mush derived from earlier ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Subduction Zone
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the heavier plate dives beneath the second plate and sinks into the mantle. A region where this process occurs is known as a subduction zone, and its surface expression is known as an arc-trench complex. The process of subduction has created most of the Earth's continental crust. Rates of subduction are typically measured in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Subduction is possible because the cold oceanic lithosphere is slightly denser than the underlying asthenosphere, the hot, ductile layer in the upper mantle underlying the cold, rigid lithosphere. Once initiated, stable subduction is driven mostly by the negative buoyancy of the dens ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Convergent Plate
A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Wadati–Benioff zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types. Plate tectonics is driven by convection cells in the mantle. Convection cells are the result of heat generated by the radioactive decay of elements in the mantle escaping to the surface and the return of cool materials from the surface to the mantle. These convection cells bring ho ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geology Of The Pacific Northwest
The geology of the Pacific Northwest includes the composition (including rock, minerals, and soils), structure, physical properties and the processes that shape the Pacific Northwest region of North America. The region is part of the Ring of Fire: the subduction of the Pacific and Farallon Plates under the North American Plate is responsible for many of the area's scenic features as well as some of its hazards, such as volcanoes, earthquakes, and landslides. The geology of the Pacific Northwest is vast and complex. Most of the region began forming about 200 million years ago as the North American Plate started to drift westward during the rifting of Pangaea. Since that date, the western edge of North America has grown westward as a succession of island arcs and assorted ocean-floor rocks have been added along the continental margin. There are at least five geologic provinces in the area: the Cascade Volcanoes, the Columbia Plateau, the North Cascades, the Coast Mountains, and th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sierra Nevada (U
The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily in Nevada. The Sierra Nevada is part of the American Cordillera, an almost continuous chain of mountain ranges that forms the western "backbone" of the Americas. The Sierra runs north-south and its width ranges from to across east–west. Notable features include General Sherman, the largest tree in the world by volume; Lake Tahoe, the largest alpine lake in North America; Mount Whitney at , the highest point in the contiguous United States; and Yosemite Valley sculpted by glaciers from one-hundred-million-year-old granite, containing high waterfalls. The Sierra is home to three national parks, twenty wilderness areas, and two national monuments. These areas include Yosemite, Sequoia, and Kings Canyon National Parks; and Devils ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Klamath Mountains
The Klamath Mountains are a rugged and lightly populated mountain range in northwestern California and southwestern Oregon in the western United States. As a mountain system within both the greater Pacific Coast Ranges and the California Coast Ranges, the Klamath Mountains have a varied geology, with substantial areas of serpentinite and marble, and a climate characterized by moderately cold winters with very heavy snowfall and warm, very dry summers with limited rainfall, especially in the south. As a consequence of the geology and soil types, the mountains harbor several endemic or near-endemic trees, forming one of the largest collections of conifers in the world. The mountains are also home to a diverse array of fish and animal species, including black bears, large cats, owls, eagles, and several species of Pacific salmon. Millions of acres in the mountains are managed by the United States Forest Service. The northernmost and largest sub-range of the Klamath Mountains are the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanic
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 are diverging or converging, and most are found underwater. For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary, deep in the Earth. This results in hotspot volcanism, of which the Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plate ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Golconda Thrust
The Golconda Thrust is a major oceanic terrane that was thrust over central and northern Nevada, North America, in possibly sometime between the Late Permian and the late Jurassic. It is considered equivalent to the Tobin thrust fault. It contains the Havallah sequence. Timing the Golconda Thrust The time of the Golconda Thrust is not perfectly clear, and it may pre-date the Sonoma orogeny. Other references suspect it appears to have thrust during the Sonoma orogeny. See also * Geology of Nevada * Golconda, Nevada * Sonomia Terrane The Sonomia Terrane is a geologic crustal block known as a "terrane" whose remnants today lie in northwest Nevada. The terrane acquired its name from the Sonoma Range in that region. The Sonomia Terrane is associated with the Golconda Thrust, a s ... References External links and references One link {{geology-stub Geology of Nevada Terranes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Argillite
:''"Argillite" may also refer to Argillite, Kentucky.'' Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts of silt-sized particles. The argillites grade into shale when the fissile layering typical of shale is developed. Another name for poorly lithified argillites is ''mudstone''. These rocks, although variable in composition, are typically high in aluminium and silica with variable alkali and alkaline earth cations. The term ''pelitic'' or ''pelite'' is often applied to these sediments and rocks. Metamorphism of argillites produces slate, phyllite, and pelitic schist. Belt Supergroup The Belt Supergroup, an assemblage of rocks of late Precambrian (Mesoproterozoic) age, includes thick sequences of argillite, as well as other metamorphosed or semi-metamorphosed mudstones.Schieber, J. 1990. Significance of styles of epicontinental shale sedime ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Conglomerate (geology)
Conglomerate () is a clastic sedimentary rock that is composed of a substantial fraction of rounded to subangular gravel-size clasts. A conglomerate typically contains a matrix of finer-grained sediments, such as sand, silt, or clay, which fills the interstices between the clasts. The clasts and matrix are typically cemented by calcium carbonate, iron oxide, silica, or hardened clay. Conglomerates form by the consolidation and lithification of gravel. They can be found in sedimentary rock sequences of all ages but probably make up less than 1 percent by weight of all sedimentary rocks. In terms of origin and depositional mechanisms, they are closely related to sandstones and exhibit many of the same types of sedimentary structures, e.g., tabular and trough cross-bedding and graded bedding.Boggs, S. (2006) ''Principles of Sedimentology and Stratigraphy.'', 2nd ed. Prentice Hall, New York. 662 pp. Friedman, G.M. (2003) ''Classification of sediments and sedimentary rocks.'' In G ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
