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74-510: The Columbia Plateau Province is a large igneous province of flood basalts erupted in Miocene and early Pliocence epochs across the states of Washington , Oregon , Idaho , Nevada , and California . The province was uplifted and divided into great blocks by faults or monoclinal flexures which were exposed to long-lasting denudation in a mid-Tertiary cycle of erosion. They were then broadly elevated again with renewed movement on some of

148-449: A consequence of the initial hot-spot activity in ocean basins as well as on continents. It is possible to track the hot spot back to the flood basalts of a large igneous province; the table below correlates large igneous provinces with the track of a specific hot spot. Eruptions or emplacements of LIPs appear to have, in some cases, occurred simultaneously with oceanic anoxic events and extinction events . The most important examples are

222-423: A high proportion of dykes relative to country rocks, particularly when the width of the linear field is less than 100 km. The dykes have a typical width of 20–100 m, although ultramafic dykes with widths greater than 1 km have been reported. Dykes are typically sub-vertical to vertical. When upward flowing (dyke-forming) magma encounters horizontal boundaries or weaknesses, such as between layers in

296-517: A large proportion (>75%) of the total igneous volume has been emplaced. They are dominantly mafic, but also can have significant ultramafic and silicic components, and some are dominated by silicic magmatism." This definition places emphasis on the high magma emplacement rate characteristics of the LIP event and excludes seamounts, seamount groups, submarine ridges and anomalous seafloor crust. The definition has since been expanded and refined, and remains

370-441: A sedimentary deposit, the magma can flow horizontally creating a sill. Some sill provinces have areal extents >1000 km. A series of related sills that were formed essentially contemporaneously (within several million years) from related dikes comprise a LIP if their area is sufficiently large. Examples include: Volcanic rifted margins are found on the boundary of large igneous provinces. Volcanic margins form when rifting

444-500: A solid convective mantle above a liquid core . The mantle's flow is driven by the descent of cold tectonic plates during subduction and the complementary ascent of mantle plumes of hot material from lower levels. The surface of the Earth reflects stretching, thickening and bending of the tectonic plates as they interact. Ocean-plate creation at upwellings, spreading and subduction are well accepted fundamentals of plate tectonics, with

518-406: A temporary shallow sheet on a dead level of clay, or playa, in a basin center, but the sheet of water vanishes in the warm season ( dry lake ) and the stream shrinks far up its course, the absolutely barren clay floor of the playa, impassable when wet, becomes firm enough for crossing when dry. One of the southwestern basins, with its floor below sea-level, has a plain of salt in its center. A few of

592-446: A very triangular shape. This formation is known as a triangular facet ; however, this landform is not limited to fault scarps. Fault scarps may vary in size from a few centimeters to many meters. Fault-line scarps are typically formed due to the differential erosion of weaker rocks along a fault. Such erosion, occurring over long time periods, may shift a physical cliff far from the actual fault location, which may be buried beneath

666-627: A volcanic province), and volcanic rifted margins . Mafic basalt sea floors and other geological products of 'normal' plate tectonics were not included in the definition. Most of these LIPs consist of basalt, but some contain large volumes of associated rhyolite (e.g. the Columbia River Basalt Group in the western United States); the rhyolite is typically very dry compared to island arc rhyolites, with much higher eruption temperatures (850 °C to 1000 °C) than normal rhyolites. Some LIPs are geographically intact, such as

740-554: A work in progress. Some new definitions of LIP include large granitic provinces such as those found in the Andes Mountains of South America and in western North America. Comprehensive taxonomies have been developed to focus technical discussions. Sub-categorization of LIPs into large volcanic provinces (LVP) and large plutonic provinces (LPP), and including rocks produced by normal plate tectonic processes, have been proposed, but these modifications are not generally accepted. LIP

814-400: Is a common geochemical proxy used to detect massive volcanism in the geologic record, although its foolproofness has been called into question. Jameson Land Thulean Plateau Brazilian Highlands These LIPs are composed dominantly of felsic materials. Examples include: These LIPs are comprised dominantly of andesitic materials. Examples include: This subcategory includes most of

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888-462: Is accompanied by significant mantle melting, with volcanism occurring before and/or during continental breakup. Volcanic rifted margins are characterized by: a transitional crust composed of basaltic igneous rocks, including lava flows, sills, dikes, and gabbros , high volume basalt flows, seaward-dipping reflector sequences of basalt flows that were rotated during the early stages of breakup, limited passive-margin subsidence during and after breakup, and

962-561: Is associated with subduction zones or mid-oceanic ridges, there are significant regions of long-lived, extensive volcanism, known as hotspots , which are only indirectly related to plate tectonics. The Hawaiian–Emperor seamount chain , located on the Pacific Plate , is one example, tracing millions of years of relative motion as the plate moves over the Hawaii hotspot . Numerous hotspots of varying size and age have been identified across

1036-857: Is in the Lower Colorado River Valley that an irrigation project, involving the diversion of some of the river water to the low plain of the Imperial Valley , led to disaster in 1904. The river flooded through a deliberately engineered breach of the Alamo Canal and flowed across the Imperial Valley plain into the Salton Sink , forming the Salton Sea . The endorheic Salton Sea remains, now supplied by subterranean flow from over-irrigated fields draining into

1110-779: Is located in all or parts of Oregon , Idaho , Nevada , California , Utah , New Mexico , Arizona in the Western United States; and Sonora , Chihuahua , Sinaloa , and other states southwards to the Trans-Mexican Volcanic Belt in Mexico . It involves some novel problems in its description, especially in Southern California and central Mexico. The province is characterized by numerous disconnected mountain ranges trending north and south, from 30–100 miles (48–161 km) in length,

1184-618: Is not now observable. The upper basalt layers of older LIPs may have been removed by erosion or deformed by tectonic plate collisions occurring after the layer is formed. This is especially likely for earlier periods such as the Paleozoic and Proterozoic . Giant dyke swarms having lengths over 300 km are a common record of severely eroded LIPs. Both radial and linear dyke swarm configurations exist. Radial swarms with an areal extent over 2,000 km and linear swarms extending over 1,000 km are known. The linear dyke swarms often have

1258-652: Is now frequently used to also describe voluminous areas of, not just mafic, but all types of igneous rocks. Further, the minimum threshold to be included as a LIP has been lowered to 50,000 km . The working taxonomy, focused heavily on geochemistry, is: Because large igneous provinces are created during short-lived igneous events resulting in relatively rapid and high-volume accumulations of volcanic and intrusive igneous rock, they warrant study. LIPs present possible links to mass extinctions and global environmental and climatic changes. Michael Rampino and Richard Stothers cite 11 distinct flood basalt episodes—occurring in

1332-644: Is to this newly introduced cycle of physiographic evolution that the deep canyons of the Plateau province are due. Thus the Virgin River , a northern tributary of the Colorado River , has cut a vertical slit, 1000 ft. deep, hardly wider at the top than at the bottom, in the heavy Triassic sandstones of southern Utah. However the most famous example is the Grand Canyon of Arizona , eroded by

1406-756: The Baffin Island flood basalt about 60 million years ago. Basalts from the Ontong Java Plateau show similar isotopic and trace element signatures proposed for the early-Earth reservoir. Seven pairs of hotspots and LIPs located on opposite sides of the earth have been noted; analyses indicate this coincident antipodal location is highly unlikely to be random. The hotspot pairs include a large igneous province with continental volcanism opposite an oceanic hotspot. Oceanic impacts of large meteorites are expected to have high efficiency in converting energy into seismic waves. These waves would propagate around

1480-477: The Cascade Range on the northwest. The river followed the temporary course long enough to erode a deep gorge, known as Grande Coulee , along part of its length. The lava plains are treeless and for the most part too dry for agriculture. However they support wildlife, and cattle and horses. Along parts of their eastern border, where the rainfall is a little increased by the approach of the westerly winds to

1554-497: The Colorado river across the uplifted platform of Carboniferous limestone. During the current cycle of erosion, several of the faults , whose scarps had been worn away in the previous cycle, have been brought to light again as topographic features by the removal of the weak strata along one side of the fault line, leaving the harder strata on the other side in relief. Such scarps are known as fault-line scarps, in distinction from

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1628-574: The Deccan Traps of India were not antipodal to (and began erupting several Myr before) the Chicxulub impact in Mexico. In addition, no clear example of impact-induced volcanism, unrelated to melt sheets, has been confirmed at any known terrestrial crater. Aerally extensive dike swarms , sill provinces, and large layered ultramafic intrusions are indicators of LIPs, even when other evidence

1702-869: The Mexican Plateau to central Mexico at the Trans-Mexican Volcanic Belt . Only a small part of the Basin and Range province is drained to the sea. A few intermont areas in the north-west part of the province have outlets westward via the Klamath River through the Cascade range. The Sacramento and San Joaquin Rivers from the Sierra Nevada pass through the Central Valley and California Coast Ranges to San Francisco Bay . A few basins in

1776-556: The crust towards the surface. The formation of LIPs is variously attributed to mantle plumes or to processes associated with divergent plate tectonics . The formation of some of the LIPs in the past 500 million years coincide in time with mass extinctions and rapid climatic changes , which has led to numerous hypotheses about causal relationships. LIPs are fundamentally different from any other currently active volcanoes or volcanic systems. In 1992, Coffin and Eldholm initially defined

1850-733: The Carboniferous platform one ascends in succession the Chocolate Cliffs ( Triassic sandstones), Vermilion and White Cliffs ( Jurassic sandstones), the Gray Cliffs ( Cretaceous sandstones, of remarkably cross-bedded structure, interpreted as the dunes of an ancient desert), and finally the Pink Cliffs ( Eocene strata of fluviatile and lacustrine origin) of the high, forested plateaus. Associated with these irregular escarpments are occasional rectilinear ridges,

1924-726: The Deccan Traps ( Cretaceous–Paleogene extinction event ), the Karoo-Ferrar ( Pliensbachian-Toarcian extinction ), the Central Atlantic magmatic province ( Triassic-Jurassic extinction event ), and the Siberian Traps ( Permian-Triassic extinction event ). Several mechanisms are proposed to explain the association of LIPs with extinction events. The eruption of basaltic LIPs onto the earth's surface releases large volumes of sulfate gas, which forms sulfuric acid in

1998-522: The LIP-triggered changes may be used as cases to understand current and future environmental changes. Plate tectonic theory explains topography using interactions between the tectonic plates, as influenced by viscous stresses created by flow within the underlying mantle . Since the mantle is extremely viscous, the mantle flow rate varies in pulses which are reflected in the lithosphere by small amplitude, long wavelength undulations. Understanding how

2072-481: The Rocky Mountains, there is a belt of very deep, impalpably fine soil, supposed to be a dust deposit brought from the drier parts of the plains farther west. Large igneous province A large igneous province ( LIP ) is an extremely large accumulation of igneous rocks , including intrusive ( sills , dikes ) and extrusive ( lava flows, tephra deposits), arising when magma travels through

2146-504: The aquifer. Many streams descend from the ravines only to wither away on the desert basin floors before uniting in a trunk river along the axis of a depression. Others succeed in uniting in the winter season, when evaporation is much reduced, and then their trunk flows for several additional miles only to disappear by sinking (evaporating) farther on. A few of the large streams, such as the Mojave River , when in flood may spread out in

2220-552: The atmosphere; this absorbs heat and causes substantial cooling (e.g., the Laki eruption in Iceland, 1783). Oceanic LIPs can reduce oxygen in seawater by either direct oxidation reactions with metals in hydrothermal fluids or by causing algal blooms that consume large amounts of oxygen. Large igneous provinces are associated with a handful of ore deposit types including: Enrichment in mercury relative to total organic carbon (Hg/TOC)

2294-794: The basaltic Deccan Traps in India, while others have been fragmented and separated by plate movements, like the Central Atlantic magmatic province —parts of which are found in Brazil, eastern North America, and northwestern Africa. In 2008, Bryan and Ernst refined the definition to narrow it somewhat: "Large Igneous Provinces are magmatic provinces with areal extents > 1 × 10  km , igneous volumes > 1 × 10  km and maximum lifespans of ~50 Myr that have intraplate tectonic settings or geochemical affinities, and are characterised by igneous pulse(s) of short duration (~1–5 Myr), during which

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2368-542: The basins are occupied by endorheic lakes without outlet, of which Great Salt Lake , in north-west Utah, is the largest. Other examples are Owens Lake and Mono Lake in California. Several smaller lakes occur in the basins of western Nevada, immediately east of the Sierra Nevada. During Pleistocene times all these lacustrine basins were occupied by lakes of much greater depth and larger size. The outlines of

2442-523: The blocks are monoclinal in structure as well as in attitude. Here, the amount of dissection is relatively moderate, for some of the fault faces are described as ravined but not yet deeply dissected. Hence these dislocations appear to be of recent date. In the Great Basin of western Utah and through most of Nevada , many of the blocks exhibit deformed structures involving folds and faults of relatively ancient ( Jurassic ) date. In fact so ancient that

2516-471: The core; roughly 15–20% have characteristics such as presence of a linear chain of sea mounts with increasing ages, LIPs at the point of origin of the track, low shear wave velocity indicating high temperatures below the current location of the track, and ratios of He to He which are judged consistent with a deep origin. Others such as the Pitcairn , Samoan and Tahitian hotspots appear to originate at

2590-446: The development of a series of cuestas : huge, south-facing, retreating escarpments of irregular outline on the edges of the higher formations farther north. Each escarpment stands forth where a resistant formation overlies a weaker, less resistant one. Each escarpment is separated from the next higher one by a broad step of weaker strata. A series of these geologic formations occurs in southern Utah , where in passing northward from

2664-424: The displacement of land surface by movement along the fault. Differential movement and erosion may occur either along older inactive geologic faults, or recent active faults . Fault scarps often involve zones of highly fractured rock and discontinuities of hard and weak consistencies of rock. Bluffs can form from upthrown blocks and can be very steep, as in the case of Pakistan's coastal cliffs. The height of

2738-460: The dramatic uplift along the fault, which exposes its surface, the fault scarp is very prone to erosion. This is especially true if the material being uplifted consists of unconsolidated sediment. Weathering, mass wasting, and water runoff can soon wear down these bluffs, sometimes resulting in V-shaped valleys along runoff channels. Adjacent V-shaped valley formations give the remaining fault spurs

2812-462: The eastern Lake Bonneville and the western Lake Lahontan water bodies are well recorded by shore lines and deltas on the enclosing slopes, hundreds of feet above the present lake surfaces. The abandoned shore lines have yielded evidence of past climatic changes second in importance only to those of the Pleistocene glaciated areas. The duration of the Pleistocene lakes was brief as compared with

2886-502: The face of the Vermilion Cliffs, so that huge slices of the cliff face have slid down and forward 1–2 miles (1.6–3.2 km), all shattered into a confused tumult of forms for a 20 miles (32 km) or more along the cliff base. Volcanic features occur in abundance in the Plateau province. Some of the high plateaus in the north are capped with remnants of heavy lava flows of early eruption. A group of large volcanoes occurs on

2960-480: The fault face. They are already somewhat battered and dissected by erosion. The most important line of cliffs of this class is associated with the western and southern boundary of the Plateau Province where it was uplifted from the lower ground. The few rivers of the region must have reached the quiescence of old age in the earlier cycle, but were revived by uplift to a vigorous youth in the current cycle. It

3034-417: The faults. The current erosion cycle started in the late Tertiary, when the deep canyons of the region were trenched. The results of the first cycle of erosion are seen in the widespread exposure of the resistant Carboniferous limestone as a broad platform in the southwestern area of greater uplift through central Arizona where the less resistant overlying formations have been eroded away. They are also seen in

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3108-425: The higher ranges reaching altitudes of 8,000–10,000 feet (2,400–3,000 m), separated by broad, intermontane desert plains or basins at altitudes varying from sea-level (or a little less) in the southwest, to 4,000–5,000 feet (1,200–1,500 m) farther inland. It is an arid region. Many of the intermontane plains , occurring mostly in the north, appear to be heavily aggraded with mountain waste. Others, mostly in

3182-462: The initial form of the uplifted blocks can hardly be perceived. Some of them still retain along one side the highly significant feature of a relatively simple base-line, transecting hard and soft structures alike indicating the faulted margin of a tilted block. Here the less uplifted blocks are now heavily aggraded with waste from the dissected ranges. The waste takes the form of huge alluvial fans, formed chiefly by occasional boulder-bearing floods from

3256-401: The interaction between mantle flow and lithosphere elevation influences formation of LIPs is important to gaining insights into past mantle dynamics. LIPs have played a major role in the cycles of continental breakup, continental formation, new crustal additions from the upper mantle , and supercontinent cycles . Earth has an outer shell made of discrete, moving tectonic plates floating on

3330-411: The large-scale plate tectonic circulation in which they are imbedded. Images reveal continuous but convoluted vertical paths with varying quantities of hotter material, even at depths where crystallographic transformations are predicted to occur. A major alternative to the plume model is a model in which ruptures are caused by plate-related stresses that fractured the lithosphere, allowing melt to reach

3404-583: The limestone platform south of the Grand Canyon, culminating in Mount San Francisco (Humphreys Peak) (12,794 feet (3,900 m), a moderately dissected cone, and associated with many more recent smaller cones and freshlooking lava flows. Mount Taylor in western New Mexico is of similar age, but here dissection seems to have advanced farther, probably because of the weaker nature of the underlying rocks. The dissection has resulted in removing

3478-457: The lower efficiency of kinetic energy conversion into seismic energy is not expected to create an antipodal hotspot. A second impact-related model of hotspot and LIP formation has been suggested in which minor hotspot volcanism was generated at large-body impact sites and flood basalt volcanism was triggered antipodally by focused seismic energy. This model has been challenged because impacts are generally considered seismically too inefficient, and

3552-410: The mountains formed by the folding were worn down to the lowland stage of old age before the block-faulting occurred. When this old-mountain lowland was broken into blocks and the blocks were tilted, their attitude, but not their structure, was monoclinal. In this new attitude, they have been so maturely re-dissected in the current new cycle of erosion as to have gained elaborately carved forms in which

3626-472: The mountains. Each fan heads in a ravine at the mountain base and becomes laterally confluent with adjacent fans as it stretches several miles forward with decreasing slope and increasing fineness of material. In the upper southern part of the Basin and Range Province, in the Mojave Desert of California, and Sonoran Desert of southern California and Arizona (U.S.) and northern Sonora (Mexico) states,

3700-564: The order of 1 million cubic kilometers. In most cases, the majority of a basaltic LIP's volume is emplaced in less than 1 million years. One of the conundra of such LIPs' origins is to understand how enormous volumes of basaltic magma are formed and erupted over such short time scales, with effusion rates up to an order of magnitude greater than mid-ocean ridge basalts. The source of many or all LIPs are variously attributed to mantle plumes, to processes associated with plate tectonics or to meteorite impacts. Although most volcanic activity on Earth

3774-441: The original fault scarps . They are peculiar in having their altitude dependent on the depth of revived erosion, instead of the amount of faulting, and they are sometimes topographically reversed, in that the revived scarp overlooks a lowland worn on a weak formation in the upheaved fault-block. Another consequence of revived erosion is seen in the occurrence of great landslides , where the removal of weak ( Permian ) clays has sapped

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3848-603: The past 250 million years—which created volcanic provinces and oceanic plateaus and coincided with mass extinctions. This theme has developed into a broad field of research, bridging geoscience disciplines such as biostratigraphy , volcanology , metamorphic petrology , and Earth System Modelling . The study of LIPs has economic implications. Some workers associate them with trapped hydrocarbons. They are associated with economic concentrations of copper–nickel and iron. They are also associated with formation of major mineral provinces including platinum group element deposits and, in

3922-545: The plains are higher and has disclosed the many lava sheets which build up the plains, occasionally revealing a buried mountain in which the superposed river has cut an even narrower canyon. One of the most remarkable features of the Intermediate Province is seen in the temporary course taken by the Columbia River across the plains, while its canyon was obstructed by Pleistocene glaciers that came from

3996-403: The pre-existent land forms over most of its extent. Some of the flows are still so young as to preserve their scoriaceous surface. Here, the shore-line of the lava contours evenly around the spurs and enters, bay-like, into the valleys of the enclosing mountains, occasionally isolating an outlying mass. Other parts of the lava flood are much older and have been more or less deformed and eroded. Thus

4070-558: The presence of a lower crust with anomalously high seismic P-wave velocities in lower crustal bodies, indicative of lower temperature, dense media. The early volcanic activity of major hotspots, postulated to result from deep mantle plumes, is frequently accompanied by flood basalts. These flood basalt eruptions have resulted in large accumulations of basaltic lavas emplaced at a rate greatly exceeding that seen in contemporary volcanic processes. Continental rifting commonly follows flood basalt volcanism. Flood basalt provinces may also occur as

4144-402: The present cycle introduced, inequalities of surface due to renewed faulting were again introduced. These still appear as cliffs, of more nearly rectilinear front than the retreating escarpments formed in the previous cycle. These cliffs are peculiar in gradually passing from one formation to another, and in having a height dependent on the displacement of the fault rather than on the structures in

4218-443: The provinces included in the original LIP classifications. It is composed of continental flood basalts, oceanic flood basalts, and diffuse provinces. Fault scarp A fault scarp is a small step-like offset of the ground surface in which one side of a fault has shifted vertically in relation to the other. The topographic expression of fault scarps results from the differential erosion of rocks of contrasting resistance and

4292-423: The ranges are well dissected and some of the intermontane depressions have rock floors with gentle, centripetal slopes. This area also has huge alluvial fans , with heads at canyons exiting the mountains, and laterally confluent with adjacent fans as they extend for miles with rather consistent slopes. The Basin and Range Province extends southeast down into Chihuahua state in northeast Mexico, and far south along

4366-419: The scarp formation tends to be defined in terms of the vertical displacement along the fault. Active scarp faults may reflect rapid tectonic displacement and can be caused by any type of fault including strike-slip faults . Vertical displacement of ten meters may occur in fault scarps in volcanic bedrock, but is usually the result of multiple episodic movements of 5 to 10 meters per tectonic event. Due to

4440-407: The silicic LIPs, silver and gold deposits. Titanium and vanadium deposits are also found in association with LIPs. LIPs in the geological record have marked major changes in the hydrosphere and atmosphere , leading to major climate shifts and maybe mass extinctions of species. Some of these changes were related to rapid release of greenhouse gases from the lithosphere to the atmosphere. Thus

4514-480: The smaller cones and exposing many lava conduits or pipes in the form of volcanic necks or buttes. The Henry Mountains in southwestern Utah are peculiar in owing their relief to the doming or blistering up of the plateau strata by the underground intrusion of large bodies or cisterns (laccolites) of lava, now more or less exposed by erosion. The large Basin and Range Province is a basin and range topography resulting from crustal extension ( extensional tectonics ). It

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4588-417: The south, are valleys also heavily aggraded by mountain erosion. The structure of the region previous to faulting was dependent on long antecedent processes of accumulation and deformation and the surface of the region then was dependent on the amount of erosion suffered in the prefaulting cycle. When the region was broken into fault blocks and the blocks were uplifted and tilted, the back slope of each block

4662-534: The southeast have outlet by the Rio Grande to the Gulf of Mexico . A much larger but still narrow medial area is drained southwestward by the Colorado River to the head of the Gulf of California , where this large and very turbid river has formed the extensive Colorado River Delta , north of which the former head of the gulf is now cut off from the sea and laid bare by evaporation as a plain below sea-level. It

4736-465: The surface from shallow heterogeneous sources. The high volumes of molten material that form the LIPs is postulated to be caused by convection in the upper mantle, which is secondary to the convection driving tectonic plate motion. It has been proposed that geochemical evidence supports an early-formed reservoir that survived in the Earth's mantle for about 4.5 billion years. Molten material is postulated to have originated from this reservoir, contributing

4810-432: The surface topography. The convective circulation drives up-wellings and down-wellings in Earth's mantle that are reflected in local surface levels. Hot mantle materials rising up in a plume can spread out radially beneath the tectonic plate causing regions of uplift. These ascending plumes play an important role in LIP formation. When created, LIPs often have an areal extent of a few million square kilometers and volumes on

4884-458: The term "large igneous province" as representing a variety of mafic igneous provinces with areal extent greater than 100,000 km that represented "massive crustal emplacements of predominantly mafic (magnesium- and iron-rich) extrusive and intrusive rock, and originated via processes other than 'normal' seafloor spreading." That original definition included continental flood basalts , oceanic plateaus , large dike swarms (the eroded roots of

4958-712: The time since the dislocation of the faulted blocks, as is shown by the small dimensions of the lacustrine beaches compared to the great volume of the ravine-heading fans on which the beaches often lie. The Intermediate Province is located in parts of Washington , Oregon and Idaho . The lava plains of the Columbia River Basin are among the most extensive volcanic outpourings in the world. They cover over 210,000 square kilometres (81,000 sq mi) in southeastern Washington, eastern Oregon, and southwestern Idaho, and are known to be 4,000 feet (1,200 m) deep in some river gorges. The lava completely buries

5032-472: The top of large, transient, hot lava domes (termed superswells) in the mantle. The remainder appear to originate in the upper mantle and have been suggested to result from the breakup of subducting lithosphere. Recent imaging of the region below known hotspots (for example, Yellowstone and Hawaii) using seismic-wave tomography has produced mounting evidence that supports relatively narrow, deep-origin, convective plumes that are limited in region compared to

5106-526: The uplifted, dislocated and dissected lava sheets of Yellowstone National Park in the Rocky Mountains on the east (at the headwaters of the Snake River ) are associated with the older lavas of the Columbian plains. The Columbia River has entrenched itself in a canyon-like valley around the northern and Western side of the lava plains. The Snake River has cut a deeper canyon farther southeast where

5180-399: The upwelling of hot mantle materials and the sinking of the cooler ocean plates driving the mantle convection. In this model, tectonic plates diverge at mid-ocean ridges , where hot mantle rock flows upward to fill the space. Plate-tectonic processes account for the vast majority of Earth's volcanism . Beyond the effects of convectively driven motion, deep processes have other influences on

5254-725: The work of extensive erosion on monoclinal structures. A good example of this is Echo Cliffs lying east of the Painted Desert . The Mogollon Rim escarpment is part of the transition zone between the Mogollon Plateau of the Colorado Plateau Province and the Sonoran Desert of the Basin and Range Province . With the renewal of uplift by which the earlier cycle of erosion was interrupted and

5328-399: The world and reconverge close to the antipodal position; small variations are expected as the seismic velocity varies depending upon the route characteristics along which the waves propagate. As the waves focus on the antipodal position, they put the crust at the focal point under significant stress and are proposed to rupture it, creating antipodal pairs. When the meteorite impacts a continent,

5402-415: The world. These hotspots move slowly with respect to one another but move an order of magnitude more quickly with respect to tectonic plates, providing evidence that they are not directly linked to tectonic plates. The origin of hotspots remains controversial. Hotspots that reach the Earth's surface may have three distinct origins. The deepest probably originate from the boundary between the lower mantle and

5476-418: Was a part of the previously eroded surface and the face of the block was a surface of fracture. The present form of the higher blocks is more or less affected by erosion since faulting, while many of the lower blocks have been buried under the waste of the higher ones. In the north, where dislocations have invaded the field of the horizontal Columbian lavas, as in southeastern Oregon and northeastern California,

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