The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south.
74-510: The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred from approximately 160 million years (Ma) ago to around 50 Ma. This orogeny was caused by the subduction of the oceanic Farallon Plate underneath the continental North American Plate . Crustal thickening that led to mountain building was caused by a combination of compressive forces and conductive heating initiated by subduction, which led to deformation. The Sevier River area of central Utah
148-737: A volcanic arc and are associated with extensional tectonics and high heat flow, often being home to seafloor spreading centers. These spreading centers are like mid-ocean ridges , though the magma composition of back-arc basins is generally more varied and contains a higher water content than mid-ocean ridge magmas. Back-arc basins are often characterized by thin, hot lithosphere. Opening of back-arc basins may arise from movement of hot asthenosphere into lithosphere, causing extension. Oceanic trenches are narrow topographic lows that mark convergent boundaries or subduction zones. Oceanic trenches average 50 to 100 km (31 to 62 mi) wide and can be several thousand kilometers long. Oceanic trenches form as
222-421: A fold axis is called a cylindrical fold . This term has been broadened to include near-cylindrical folds. Often, the fold axis is the same as the hinge line. Minor folds are quite frequently seen in outcrop; major folds seldom are except in the more arid countries. Minor folds can, however, often provide the key to the major folds they are related to. They reflect the same shape and style, the direction in which
296-601: A fold-thrust belt on a regional scale. At the local scale segments of the belt are connected by transverse zones. The Charleston transverse zone mentioned earlier runs perpendicular to the thrust faults within the Sevier belt. It has been debated among geologists if this transverse zone developed during the Sevier orogeny or the Uinta/Cottonwood arch formation during the Laramide orogeny . Mapping Sevier thrusting in
370-444: A hinge need to accommodate large deformations in the hinge zone. This results in voids between the layers. These voids, and especially the fact that the water pressure is lower in the voids than outside of them, act as triggers for the deposition of minerals. Over millions of years, this process is capable of gathering large quantities of trace minerals from large expanses of rock and depositing them at very concentrated sites. This may be
444-427: A mechanism that is responsible for the veins. To summarize, when searching for veins of valuable minerals, it might be wise to look for highly folded rock, and this is the reason why the mining industry is very interested in the theory of geological folding. Anticlinal traps are formed by folding of rock. For example, if a porous sandstone unit covered with low permeability shale is folded into an anticline, it may form
518-629: A planar detachment without further fault propagation, detachment folds may form, typically of box-fold style. These generally occur above a good detachment such as in the Jura Mountains , where the detachment occurs on middle Triassic evaporites . Shear zones that approximate to simple shear typically contain minor asymmetric folds, with the direction of overturning consistent with the overall shear sense. Some of these folds have highly curved hinge-lines and are referred to as sheath folds . Folds in shear zones can be inherited, formed due to
592-621: 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
666-553: A result of bending of the subducting slab. Depth of oceanic trenches seems to be controlled by age of the oceanic lithosphere being subducted. Sediment fill in oceanic trenches varies and generally depends on abundance of sediment input from surrounding areas. An oceanic trench, the Mariana Trench , is the deepest point of the ocean at a depth of approximately 11,000 m (36,089 ft). Earthquakes are common along convergent boundaries. A region of high earthquake activity,
740-541: A strong axial planar cleavage . Folds in the rock are formed about the stress field in which the rocks are located and the rheology , or method of response to stress, of the rock at the time at which the stress is applied. The rheology of the layers being folded determines characteristic features of the folds that are measured in the field. Rocks that deform more easily form many short-wavelength, high-amplitude folds. Rocks that do not deform as easily form long-wavelength, low-amplitude folds. Layers of rock that fold into
814-435: A thrust fault cuts up section from one detachment level to another. Displacement over this higher-angle ramp generates the folding. Fault propagation folds or tip-line folds are caused when displacement occurs on an existing fault without further propagation. In both reverse and normal faults this leads to folding of the overlying sequence, often in the form of a monocline . When a thrust fault continues to displace above
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#1732776816523888-504: Is accommodated by slip between the pages of the book. The fold formed by the compression of competent rock beds is called "flexure fold". Typically, folding is thought to occur by simple buckling of a planar surface and its confining volume. The volume change is accommodated by layer parallel shortening the volume, which grows in thickness . Folding under this mechanism is typical of a similar fold style, as thinned limbs are shortened horizontally and thickened hinges do so vertically. If
962-417: Is also a feature of many igneous intrusions and glacier ice. Folding of rocks must balance the deformation of layers with the conservation of volume in a rock mass. This occurs by several mechanisms. Flexural slip allows folding by creating layer-parallel slip between the layers of the folded strata, which, altogether, result in deformation. A good analogy is bending a phone book, where volume preservation
1036-405: 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 hot mantle material to the surface along spreading centers creating new crust. As this new crust is pushed away from the spreading center by
1110-531: Is evidence that suggests late Sevier faults were active during the early Laramide. The majority of Sevier deformation occurred west of Laramide deformation, but there is some geographic overlap between the eastern Sevier margin and the western Laramide margin. In southwestern Utah, Sevier thrusts may have remained active until the Eocene, while Laramide deformation began in the Late Cretaceous . Since
1184-444: Is likely that the plate may break along the boundary of continental and oceanic crust. Seismic tomography reveals pieces of lithosphere that have broken off during convergence. Subduction zones are areas where one lithospheric plate slides beneath another at a convergent boundary due to lithospheric density differences. These plates dip at an average of 45° but can vary. Subduction zones are often marked by an abundance of earthquakes,
1258-412: Is most characteristic of oceanic volcanic arcs, though this is also found in continental volcanic arcs above rapid subduction (>7 cm/year). This series is relatively low in potassium . The more oxidized calc-alkaline series , which is moderately enriched in potassium and incompatible elements, is characteristic of continental volcanic arcs. The alkaline magma series (highly enriched in potassium)
1332-425: Is relatively weak. When rock behaves as a fluid, as in the case of very weak rock such as rock salt, or any rock that is buried deeply enough, it typically shows flow folding (also called passive folding , because little resistance is offered): the strata appear shifted undistorted, assuming any shape impressed upon them by surrounding more rigid rocks. The strata simply serve as markers of the folding. Such folding
1406-415: Is scraped from the subducting lithosphere and emplaced against the overriding lithosphere. These sediments include igneous crust, turbidite sediments, and pelagic sediments. Imbricate thrust faulting along a basal decollement surface occurs in accretionary wedges as forces continue to compress and fault these newly added sediments. The continued faulting of the accretionary wedge leads to overall thickening of
1480-427: Is sometimes present in the deeper continental interior. The shoshonite series, which is extremely high in potassium, is rare but sometimes is found in volcanic arcs. The andesite member of each series is typically most abundant, and the transition from basaltic volcanism of the deep Pacific basin to andesitic volcanism in the surrounding volcanic arcs has been called the andesite line. Back-arc basins form behind
1554-454: Is the midpoint of the limb. The axial surface is defined as a plane connecting all the hinge lines of stacked folded surfaces. If the axial surface is planar, it is called an axial plane and can be described in terms of strike and dip . Folds can have a fold axis . A fold axis "is the closest approximation to a straight line that when moved parallel to itself, generates the form of the fold". (Ramsay 1967). A fold that can be generated by
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#17327768165231628-722: Is the namesake of this event. The Sevier Fold and Thrust Belt extends from southern California near the Mexican border to Canada. Basin and Range faults cut the older Sevier thrust faults. The Sevier orogeny was preceded by several other mountain-building events including the Nevadan orogeny , the Sonoman orogeny , and the Antler orogeny , and partially overlapped in time and space with the Laramide orogeny . Early Sevier thrusting began well before initial Laramide deformation. However, there
1702-414: Is thought to be a parallel model of the Sevier and Laramide events so there are possibly answers to this question in this modern model. Explanations may include a combination of plate motion rates increasing, the underriding oceanic plate becoming younger as the older portion subducts, and thus the underriding plate being hotter and more buoyant. A study on calcite twinning and carbonate relationships with
1776-821: The Basin and Range Province suggests Sevier structures curve around the Uinta/Cottonwood arch defining the Uinta recess. Looking closely at Sevier faults in American Fork Canyon indicate that these faults are the oldest in the Charleston transverse zone suggested by cross cutting relationships observed in the area. The Basin and Range Province extending across Nevada , into western Utah , and south into Mexico now consists of N-S normal faulting due to crustal extension. If these normal faults show any extension in late Eocene to early Miocene , this could be evidence
1850-502: The Wadati–Benioff zone , generally dips 45° and marks the subducting plate. Earthquakes will occur to a depth of 670 km (416 mi) along the Wadati-Benioff margin. Both compressional and extensional forces act along convergent boundaries. On the inner walls of trenches, compressional faulting or reverse faulting occurs due to the relative motion of the two plates. Reverse faulting scrapes off ocean sediment and leads to
1924-648: The Cordilleran passive margin east. The Sevier meets the Laramide orogenic belt on its eastern side. The Sevier and Laramide combination is similar to the modern day Andean margin in Chile . They are comparable because the younger Laramide faults and structures were a geometric response to the shallow dipping Sevier thrusts. The location of the eastern edge of the Sevier orogeny was determined by conglomerates largely made up of boulders that would have been shed from
1998-567: The Garden Valley thrust system has a direct link to the Sevier thrust belt. The interpretation of this data led to the central Nevada thrust belt as being an interior section of the Sevier. This correlation provides evidence that the Sevier thrust belt was a result of compression moving eastward through the North American plate. Thinning of the Cordilleran has previously been thought to be evidence and reason for flat subduction in
2072-504: The Laramide orogenic event. Sevier shortening has been recorded throughout much of the western United States as far east as Minnesota in the Cretaceous Greenhorn Limestone as preserved by calcite twinning. The distance of stress transfer is roughly equivalent to more than 2000 km. The E-W shortening shown in calcite twinning of the Sevier is parallel to today's principal stresses in the western interior of
2146-645: The North American plate. Voluminous volcanism is also associated with the Sevier Orogeny. Volcanic activity can be observed at modern subduction zones, (such as along the west coast of South America) like the one that caused the Sevier Orogeny. Several volcanic flare-ups occurred in the Sierra Nevada arc, associated with the Sevier Orogeny: one from 170 Ma to 150 Ma, and one from 100 Ma to 85 Ma. Volcanic centers migrated generally eastward during
2220-503: The Sevier and Laramide orogenic events. However, isotopic data suggests that preservation of Cordilleran lithosphere implies Cordilleran thinning is not a sufficient answer for Sevier and Laramide flat subduction. This implies thinning and shearing of the Cordilleran was confined to the fore-arc region. Data suggests throughout the Sevier-Laramide thrusting the crust was also uplifted and extended. The modern Chilean subduction
2294-455: The Sevier and Laramide orogenies occurred at similar times and places, they are sometimes confused. In general the Sevier orogeny defines an older, more western compressional event that took advantage of weak bedding planes in overlying Paleozoic and Mesozoic sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “ thin-skinned ” thrust faults that generally get younger to
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2368-629: The Sevier are located furthest west with each newer thrust cutting the older thrust. This pattern caused the older thrusts to ride on top of the younger thrusts as they moved eastward. The Paris-Willard thrust in Utah was determined to be the oldest thrust in the series using this pattern. The youngest thrust is the Hogback in Wyoming. The Sevier thrust belt in Utah can be divided in two, north of Salt Lake City and South of Salt Lake City. The thrusts to
2442-434: The Sevier orogenic belt showed that shortening directions were parallel to the thrust faulting, which was an E-W direction. Differential stress magnitudes determined from calcite twinning showed a decreasing trend exponentially toward the craton . Differential stresses causing compressional deformation in the Sevier thrust were greater than 150 MPa. The E-W contraction during the Sevier changed to roughly N-S oblique during
2516-468: The Sevier orogenic event collapsing after deactivation. Thickening of the crust due to Sevier and Laramide faulting is thought to have led to current Basin and Range extension throughout the Cenozoic. This could have caused the Charleston thrust fault to reactivate as an extensional fault. The Charleston transverse zone contained high angle faults which suggests it initiated as a response to connecting
2590-407: The Sevier thrusting migrated eastward, the sedimentary basins also migrated eastward. Balanced cross-sections show that significant erosion of this Sevier-age synorogenic sediment has occurred. Convergent boundary 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,
2664-517: The Tethyan suture zone (the Alps – Zagros – Himalaya mountain belt). The oceanic crust contains hydrated minerals such as the amphibole and mica groups. During subduction, oceanic lithosphere is heated and metamorphosed, causing breakdown of these hydrous minerals, which releases water into the asthenosphere. The release of water into the asthenosphere leads to partial melting. Partial melting allows
2738-441: The accommodation of strains between neighboring faults. Fault-bend folds are caused by displacement along a non-planar fault. In non-vertical faults, the hanging-wall deforms to accommodate the mismatch across the fault as displacement progresses. Fault bend folds occur in both extensional and thrust faulting. In extension, listric faults form rollover anticlines in their hanging walls. In thrusting, ramp anticlines form whenever
2812-457: The asthenosphere and volcanism. Both dehydration and partial melting occur along the 1,000 °C (1,830 °F) isotherm, generally at depths of 65 to 130 km (40 to 81 mi). Some lithospheric plates consist of both continental and oceanic lithosphere . In some instances, initial convergence with another plate will destroy oceanic lithosphere, leading to convergence of two continental plates. Neither continental plate will subduct. It
2886-493: The axis of the fold. Those with limbs of relatively equal length are termed symmetrical , and those with highly unequal limbs are asymmetrical . Asymmetrical folds generally have an axis at an angle to the original unfolded surface they formed on. Vergence is calculated in a direction perpendicular to the fold axis. Folds that maintain uniform layer thickness are classed as concentric folds. Those that do not are called similar folds . Similar folds tend to display thinning of
2960-661: The belt is not entirely agreed upon by researchers. However, Sevier deformation had begun by the Jurassic. Deformation in the southern portion of the Sevier fold and thrust belt began around 160 Ma. Strain was transferred eastward to the Keystone thrust by 99 Ma. In northern Utah, the Willard thrust sheet was emplaced around 120 Ma. Strain was progressively transferred to the Hogsback Thrust in western Wyoming. Faults near
3034-412: The closures of the major folds lie, and their cleavage indicates the attitude of the axial planes of the major folds and their direction of overturning A fold can be shaped like a chevron , with planar limbs meeting at an angular axis, as cuspate with curved limbs, as circular with a curved axis, or as elliptical with unequal wavelength . Fold tightness is defined by the size of the angle between
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3108-519: The dense oceanic lithosphere subducts beneath the less dense continental lithosphere. An accretionary wedge forms on the continental crust as deep-sea sediments and oceanic crust are scraped from the oceanic plate. Volcanic arcs form on continental lithosphere as the result of partial melting due to dehydration of the hydrous minerals of the subducting slab. Some lithospheric plates consist of both continental and oceanic crust. Subduction initiates as oceanic lithosphere slides beneath continental crust. As
3182-571: The east. In contrast, the Laramide orogeny produced “basement-cored” uplifts that often took advantage of pre-existing faults that formed during rifting in the late Precambrian during the breakup of the supercontinent Rodinia or during the Ancestral Rocky Mountains orogeny. The Sevier orogenic belt consisted of a series of thin plates along gently dipping west thrust sheets and moving from west to east. These thin skinned thrusts moved late Precambrian to Mesozoic age rock of
3256-663: The eastern and steepest edge of the rising mountains. Such conglomerates can be seen throughout Utah in Echo Canyon, the Red Narrows in Spanish Fork Canyon, and in Leamington Canyon near Delta, Utah . Today Sevier faults at the surface have been broken up and tilted steeply from their original gently dipping positions due to the extension of the Basin and Range faulting. The earliest thrusts of
3330-409: The effects of a high-level igneous intrusion e.g. above a laccolith . The fold hinge is the line joining points of maximum curvature on a folded surface. This line may be either straight or curved. The term hinge line has also been used for this feature. A fold surface seen perpendicular to its shortening direction can be divided into hinge and limb portions; the limbs are the flanks of
3404-450: The fold's limbs (as measured tangential to the folded surface at the inflection line of each limb), called the interlimb angle. Gentle folds have an interlimb angle of between 180° and 120°, open folds range from 120° to 70°, close folds from 70° to 30°, and tight folds from 30° to 0°. Isoclines , or isoclinal folds , have an interlimb angle of between 10° and zero, with essentially parallel limbs. Not all folds are equal on both sides of
3478-409: The fold, and the limbs converge at the hinge zone. Within the hinge zone lies the hinge point, which is the point of minimum radius of curvature (maximum curvature) of the fold. The crest of the fold represents the highest point of the fold surface whereas the trough is the lowest point. The inflection point of a fold is the point on a limb at which the concavity reverses; on regular folds, this
3552-439: The folding deformation cannot be accommodated by a flexural slip or volume-change shortening (buckling), the rocks are generally removed from the path of the stress. This is achieved by pressure dissolution , a form of metamorphic process, in which rocks shorten by dissolving constituents in areas of high strain and redepositing them in areas of lower strain. Folds generated in this way include examples in migmatites and areas with
3626-485: The formation of an accretionary wedge. Reverse faulting can lead to megathrust earthquakes . Tensional or normal faulting occurs on the outer wall of the trench, likely due to bending of the downgoing slab. A megathrust earthquake can produce sudden vertical displacement of a large area of ocean floor. This in turn generates a tsunami . Some of the deadliest natural disasters have occurred due to convergent boundary processes. The 2004 Indian Ocean earthquake and tsunami
3700-420: The formation of newer crust, it cools, thins, and becomes denser. Subduction begins when this dense crust converges with a less dense crust. The force of gravity helps drive the subducting slab into the mantle. As the relatively cool subducting slab sinks deeper into the mantle, it is heated, causing hydrous minerals to break down. This releases water into the hotter asthenosphere, which leads to partial melting of
3774-471: The full spectrum of metamorphic rocks , and even as primary flow structures in some igneous rocks . A set of folds distributed on a regional scale constitutes a fold belt , a common feature of orogenic zones . Folds are commonly formed by shortening of existing layers, but may also be formed as a result of displacement on a non-planar fault ( fault bend fold ), at the tip of a propagating fault ( fault propagation fold ), by differential compaction or due to
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#17327768165233848-497: The leading edge of the Sevier remained active until at least the Eocene. At this time the elevated crust ran into the Colorado Plateau . The collision resulted in lateral spreading of deformation and led to a weakened lithosphere and crustal thickening. Metamorphism due to the crustal heating and thickening is prevalent between 90 and 70 Ma in the present Great Basin region. Parallel thrust faults and folds make up
3922-548: The limbs and thickening of the hinge zone. Concentric folds are caused by warping from active buckling of the layers, whereas similar folds usually form by some form of shear flow where the layers are not mechanically active. Ramsay has proposed a classification scheme for folds that often is used to describe folds in profile based upon the curvature of the inner and outer lines of a fold and the behavior of dip isogons . that is, lines connecting points of equal dip on adjacent folded surfaces: (A homocline involves strata dipping in
3996-406: The low angle thrust faults of the Sevier. The Charleston transverse zone outlines a main sidewall ramp that would have been part of the Sevier belt. To the north of the Uinta/Cottonwood arch during the Sevier orogeny there was a basement high area gently dipping to the north identified by isopach maps. Thus sediment thickened quickly to the south. To the north strata changed gradually throughout
4070-609: The mechanical layering and the contrast in properties between the layers. If the layering does begin to fold, the fold style is also dependent on these properties. Isolated thick competent layers in a less competent matrix control the folding and typically generate classic rounded buckle folds accommodated by deformation in the matrix. In the case of regular alternations of layers of contrasting properties, such as sandstone-shale sequences, kink-bands, box-folds and chevron folds are normally produced. Many folds are directly related to faults, associated with their propagation, displacement and
4144-441: The most deformed in orogenic events, the interior of continental plates can also deform. In the Sevier-Laramide orogenic events evidence for interior plate deformation includes folds , cleavage and joint fabrics, distorted fossils , persistent faulting , and calcite twinning . The Sevier fold and thrust belt was active between late Jurassic (201 - 145 Mya) through Eocene (56 - 34 Mya) time. The actual age of initiation of
4218-469: The north are much better understood because oil and gas are often associated with them. The northern portion runs through present day Utah, Idaho, and Wyoming. The southern portion stops around Las Vegas . The total crustal shortening of the northern portion was roughly 60 miles. The Sevier belt left behind many distinctive geologic features in the Wyoming and Utah region, namely recesses and salients. Transverse zones can accompany thrust faults connecting
4292-417: The oceanic lithosphere subducts to greater depths, the attached continental crust is pulled closer to the subduction zone. Once the continental lithosphere reaches the subduction zone, subduction processes are altered, since continental lithosphere is more buoyant and resists subduction beneath other continental lithosphere. A small portion of the continental crust may be subducted until the slab breaks, allowing
4366-552: The oceanic lithosphere to continue subducting, hot asthenosphere to rise and fill the void, and the continental lithosphere to rebound. Evidence of this continental rebound includes ultrahigh pressure metamorphic rocks , which form at depths of 90 to 125 km (56 to 78 mi), that are exposed at the surface. Seismic records have been used to map the torn slabs beneath the Caucasus continental – continental convergence zone, and seismic tomography has mapped detached slabs beneath
4440-540: The orientation of pre-shearing layering or formed due to instability within the shear flow. Recently deposited sediments are normally mechanically weak and prone to remobilization before they become lithified, leading to folding. To distinguish them from folds of tectonic origin, such structures are called synsedimentary (formed during sedimentation). Slump folding: When slumps form in poorly consolidated sediments, they commonly undergo folding, particularly at their leading edges, during their emplacement. The asymmetry of
4514-593: The progression of the Sevier and the transition to Laramide deformation, and by the late Cretaceous volcanism related to Farallon Plate subduction could be found as far east as the Colorado Mineral Belt, east of the leading edge of the Sevier fold and thrust belt. As Sevier thrust faults were uplifted, thrust sheet erosion occurred; those eroded sediments were then deposited where accommodation space existed. Dynamic subsidence and flexure due to crustal loading created space where sediments could accumulate. As
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#17327768165234588-399: The result of internal deformation of the plate, convergence with the opposing plate, and bending at the oceanic trench. Earthquakes have been detected to a depth of 670 km (416 mi). The relatively cold and dense subducting plates are pulled into the mantle and help drive mantle convection. In collisions between two oceanic plates, the cooler, denser oceanic lithosphere sinks beneath
4662-461: The rise of more buoyant, hot material and can lead to volcanism at the surface and emplacement of plutons in the subsurface. These processes which generate magma are not entirely understood. Where these magmas reach the surface they create volcanic arcs. Volcanic arcs can form as island arc chains or as arcs on continental crust. Three magma series of volcanic rocks are found in association with arcs. The chemically reduced tholeiitic magma series
4736-400: The same direction, though not necessarily any folding.) Folds appear on all scales, in all rock types , at all levels in the crust . They arise from a variety of causes. When a sequence of layered rocks is shortened parallel to its layering, this deformation may be accommodated in a number of ways, homogeneous shortening, reverse faulting or folding. The response depends on the thickness of
4810-526: The segments of the belt. One such zone is the Charleston transverse zone linking the Provo salient to the southern arm of the Uinta/Cottonwood arch. Although the Uinta/Cottonwood arch is a Laramide structure the Sevier helped the arch form. Another important zone is the Mount Raymond transverse zone connecting the Wyoming salient and the northern arm of the arch. While continental margins are typically
4884-471: The shaping of the curvature of the Uinta recess prior to uplift of the Uinta/Cottonwood arch. Focusing on the southern portion of the Sevier thrust belt many thrust faults can be found. One thrust system is known as the Garden Valley thrust system in the central Nevada thrust belt. Thrusts within this system include the Pahranagat, Mount Irish, and Golden Gate thrusts. These thrusts were correlated with
4958-420: The slump folds can be used to determine paleoslope directions in sequences of sedimentary rocks. Dewatering: Rapid dewatering of sandy sediments, possibly triggered by seismic activity, can cause convolute bedding. Compaction: Folds can be generated in a younger sequence by differential compaction over older structures such as fault blocks and reefs . The emplacement of igneous intrusions tends to deform
5032-523: The southward Gass Peak thrust. The Gass Peak thrust is located in the Las Vegas Range and is a Sevier age structure. This thrust may have been responsible for the largest slip of the major belt along that latitude. These thrusts were located all along the same strike. This region showed small scale extension in the Cenozoic due to reactivation of the thrusts. Such a correlation suggests that
5106-482: The surrounding country rock . In the case of high-level intrusions, near the Earth's surface, this deformation is concentrated above the intrusion and often takes the form of folding, as with the upper surface of a laccolith . The compliance of rock layers is referred to as competence : a competent layer or bed of rock can withstand an applied load without collapsing and is relatively strong, while an incompetent layer
5180-404: The thrust and a gradual curve developed around the Wyoming salient and to the south around the Provo salient. The Charleston and Mount Raymond transverse zones formed the Uinta recess indicating the recess was initiated during the Sevier orogeny. The results were interpreted to support the Charleston transverse zone forming during the Sevier orogeny to accommodate geometric changes along strike of
5254-417: The thrusts. The zone served as a linking tool of the various segments of the orogeny. The transverse zone varied throughout the region in terms of depth and displacement. The zone was later tilted and was reactivated through crustal extension. Results also support the Uinta recess forming during the Sevier orogeny due to similar geometric crustal accommodation. Displacement on Sevier aged thrust faults caused
5328-447: The warmer, less dense oceanic lithosphere. As the slab sinks deeper into the mantle, it releases water from dehydration of hydrous minerals in the oceanic crust. This water reduces the melting temperature of rocks in the asthenosphere and causes partial melting. Partial melt will travel up through the asthenosphere, eventually, reach the surface, and form volcanic island arcs . When oceanic lithosphere and continental lithosphere collide,
5402-759: The wedge. Seafloor topography plays some role in accretion, especially emplacement of igneous crust. [REDACTED] Media related to Subduction at Wikimedia Commons Fold (geology) In structural geology , a fold is a stack of originally planar surfaces, such as sedimentary strata , that are bent or curved ( "folded" ) during permanent deformation . Folds in rocks vary in size from microscopic crinkles to mountain-sized folds. They occur as single isolated folds or in periodic sets (known as fold trains ). Synsedimentary folds are those formed during sedimentary deposition. Folds form under varied conditions of stress , pore pressure , and temperature gradient , as evidenced by their presence in soft sediments ,
5476-552: Was triggered by a megathrust earthquake along the convergent boundary of the Indian plate and Burma microplate and killed over 200,000 people. The 2011 tsunami off the coast of Japan , which caused 16,000 deaths and did US$ 360 billion in damage, was caused by a magnitude 9 megathrust earthquake along the convergent boundary of the Eurasian plate and Pacific plate. Accretionary wedges (also called accretionary prisms ) form as sediment
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