The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south. Sevier Fold and Thrust Belt

The Sevier orogeny was the result of

convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more Plate tectonics, lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can ...

tectonic activity, and deformation occurred from approximately 160 million years (Ma) ago to around 50 Ma. This

orogeny Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...

was caused by the subduction of the oceanic

Farallon Plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west c ...

underneath the continental

North American Plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...

Crustal thickening Thrust tectonics or contractional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere. It is one of the three main types of tectonic regime, ...

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 The Sevier River (pronounced "severe") is a -long river in the Great Basin of southwestern Utah in the United States. Originating west of Bryce Canyon National Park, the river flows north through a chain of high farming valleys and steep canyons ...

area of central

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

is the namesake of this event.

Extent

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 Nevadan orogeny occurred along the western margin of North America during the Middle Jurassic to Early Cretaceous time which is approximately from 155 Ma to 145 Ma. Throughout the duration of this orogeny there were at least two different kin ...

, the Sonoman orogeny, and the

Antler orogeny The Antler orogeny was a tectonic event that began in the early Late Devonian with widespread effects continuing into the Mississippian and early Pennsylvanian. Most of the evidence for this event is in Nevada but the limits of its reach are un ...

, and partially overlapped in time and space with the

Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

Sevier or Laramide?

Early Sevier thrusting began well before initial Laramide deformation. However, there is evidence that suggests late Sevier faults were active during the early Laramide.Anderson, L.P., and Dinter, D.A., 2010, Deformation and sedimentation in the southern Sevier foreland, Red Hills, southwestern Utah, in Carney, S.M., Tabet, D.E., and Johnson, C.L., editors, Geology of south-central Utah: Utah Geological Association Publication 39, p. 338–366.Biek, R.F., Rowley, P.D., Anderson, J.J., Maldonado, F., Moore, D.W., Hacker, D.B., Eaton, J.G., Hereford, R., Filkorn, H.F., and Matyjasik, B., 2015, Geologic map of the Panguitch 30′ x 60′ quadrangle, Garfield, Iron, and Kane Counties, Utah: Utah Geological Survey Map, 4 plates, scale 1:62,500 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 The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

. Since 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 The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

and

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “ thin-skinned”

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

s that generally get younger to the east. In contrast, the Laramide orogeny produced “basement-cored” uplifts that often took advantage of pre-existing faults that formed during

rifting In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics. Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-graben ...

in the late Precambrian during the breakup of the supercontinent

Rodinia Rodinia (from the Russian родина, ''rodina'', meaning "motherland, birthplace") was a Mesoproterozoic and Neoproterozoic supercontinent that assembled 1.26–0.90 billion years ago and broke up 750–633 million years ago. were probably ...

or during the

Ancestral Rocky Mountains The geology of the Rocky Mountains is that of a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Northern British Columbia through cen ...

orogeny.

Geologic structures

The Sevier orogenic belt consisted of a series of thin plates along gently dipping west thrust sheets and moving from west to east.Burtner, R.G. and Nigrini, A., 1994, Thermochronology of the Idaho-Wyoming thrust belt during the Sevier Orogeny; a new, calibrated, multiprocess thermal model, AAPG Bulletin, Vol. 78, Issue 10, pp. 1586-1612. These thin skinned thrusts moved late

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

age rock of 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 Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. They are comparable because the younger Laramide faults and structures were a geometric response to the shallow dipping Sevier thrusts.Craddock, J.P. and van der Plujim, B.A., 1999, Sevier-Laramide deformation of the continental interior from calcite twinning analysis, west-central North, Tectonophysics, Vol. 205, Issue 1-3, pp. 275-286. 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 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 Delta is the largest city in Millard County, Utah, United States. It is located in the northeastern area of Millard County along the Sevier River and is surrounded by farmland. The population was 3,436 at the 2010 census. History Delta was ori ...

. 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 Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...

faulting. The earliest thrusts of 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.Hintze, L., 2005, Utah’s Spectacular Geology, Department of Geology, Brigham Young University, pp. 57, 60-62, 65. The Sevier thrust belt in Utah can be divided in two, north of

Salt Lake City Salt Lake City (often shortened to Salt Lake and abbreviated as SLC) is the Capital (political), capital and List of cities and towns in Utah, most populous city of Utah, United States. It is the county seat, seat of Salt Lake County, Utah, Sal ...

and South of Salt Lake City. The thrusts to 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 Las Vegas (; Spanish for "The Meadows"), often known simply as Vegas, is the 25th-most populous city in the United States, the most populous city in the state of Nevada, and the county seat of Clark County. The city anchors the Las Vegas ...

. The total crustal shortening of the northern portion was roughly 60 miles. TransZ

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 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.Paulsen, T. and Marshak, S., 1999, Origin of the Uinta Recess, Sevier fold-thrust belt, Utah; influence of basin and architecture on fold-thrust belt geometry, Tectonophysics, Vol. 312, Issue 2-4, pp. 203-216. While continental margins are typically 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 A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in ...

, persistent

faulting In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

, and calcite twinning. Sevierorogeny

How and when

The Sevier fold and thrust belt was active between late

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

(201 - 145 Mya) through

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

(56 - 34 Mya) time.Taylor, W.J., Bartley, J.M., Martin, M.W., Geissman, J.W., Walker, J.D., Armstrong, P.A., and Fryxell, J.E., 2000, Relations between hinterland and foreland shortening: Sevier orogeny, central North America Cordillera, Tectonophysics, Vol. 19, Issue 6, pp. 1124-1143. The actual age of initiation of 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 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 Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area of ...

. The collision resulted in lateral spreading of deformation and led to a weakened

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 sca ...

and crustal thickening.

Metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...

due to the crustal heating and thickening is prevalent between 90 and 70 Ma in the present

Great Basin The Great Basin is the largest area of contiguous endorheic basin, endorheic watersheds, those with no outlets, in North America. It spans nearly all of Nevada, much of Utah, and portions of California, Idaho, Oregon, Wyoming, and Baja California ...

region.Livacarri, R.F. and Perry, F.V., 1993, Isotopic evidence for preservation of Cordilleran lithospheric mantle during the Sevier-Laramide Orogeny, Western-United States, Geology oulder Vol. 21, Issue 8, pp. 719-722.

Studies

Transverse zones and the Uinta recess

Parallel thrust faults and folds make up 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

.Paulsen, T. and Marshak, S., 1998, Charleston transverse zone, Wasatch Mountains, Utah; structure of the Provo Salient’s northern margin, Sevier fold-thrust belt, Geological Society of America Bulletin, Vol. 116, Issue 4, pp. 512-522. Mapping Sevier thrusting in the

Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...

suggests Sevier structures curve around the Uinta/Cottonwood arch defining the Uinta recess. Looking closely at Sevier faults in

American Fork Canyon American Fork Canyon is a canyon in the Wasatch Mountains of Utah, United States. The canyon is famous for the Timpanogos Cave National Monument, which resides on its south side. It is named after the American Fork River, which runs through the b ...

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 Nevada ( ; ) is a U.S. state, state in the Western United States, Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. N ...

, into western

, and south into Mexico now consists of N-S normal faulting due to crustal extension. If these normal faults show any extension in late

to early

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

, this could be evidence 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.Livacarri, R.F., 1991, Role of crustal thickening and extensional collapse in the tectonic evolution of the Sevier-Laramide Orogeny, Western United States, Geology oulder Vol. 19, Issue 11, pp. 1104-1107. 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 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 An isopach map () illustrates thickness variations within a tabular unit, layer or stratum. Isopachs are contour lines of equal thickness over an area. Isopach maps are utilized in hydrographic survey, stratigraphy, sedimentology, structural geolo ...

maps. Thus sediment thickened quickly to the south. To the north strata changed gradually throughout 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 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 the shaping of the curvature of the Uinta recess prior to uplift of the Uinta/Cottonwood arch.

Related thrust belts

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 the southward

Gass Peak Gass Peak is the highest peak in the Las Vegas Range of Southern Nevada with a summit of 6,937 feet (2,114 m). It is easily seen to the north of the Las Vegas Valley, bordering the city of North Las Vegas. The peak is located about 20 miles (32&n ...

thrust. The Gass Peak thrust is located in the

Las Vegas Range The Las Vegas Range is an arid mountain range in Clark County, Nevada. The range is located in the southeast of the Desert National Wildlife Refuge. Geography The Las Vegas Range is a north–south range, with two main north–south ridgelines. ...

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 The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...

due to reactivation of the thrusts. Such a correlation suggests that 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.

Cordilleran and Sevier orogenesis relationships

Thinning of the Cordilleran has previously been thought to be evidence and reason for flat subduction in 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 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.

Crustal shortening

A study on calcite twinning and carbonate relationships with the Sevier orogenic belt showed that shortening directions were parallel to the thrust faulting, which was an E-W direction.

Differential stress Differential stress is the difference between the greatest and the least compressive stress experienced by an object. For both the geological and civil engineering convention \sigma_1 is the greatest compressive stress and \sigma_3 is the weakest, ...

magnitudes determined from calcite twinning showed a decreasing trend exponentially toward the

craton A craton (, , or ; from grc-gre, κράτος "strength") is an old and stable part of the continental lithosphere, which consists of Earth's two topmost layers, the crust and the uppermost mantle. Having often survived cycles of merging and ...

. 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 the Laramide orogenic event. Sevier shortening has been recorded throughout much of the western United States as far east as

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over to ...

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 the North American plate.

Sevier volcanism

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 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.

Foreland sedimentation

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 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.

References

* {{refend Orogenies of North America Cretaceous North America Eocene North America Paleocene North America Cretaceous orogenies Paleogene orogenies Eocene geology Paleocene geology Cretaceous British Columbia Cretaceous Colorado Cretaceous Montana Cretaceous geology of Utah Cretaceous geology of Wyoming Paleogene British Columbia Paleogene Colorado Paleogene Montana Paleogene geology of Utah Paleogene geology of Wyoming