Sevier orogeny
Encyclopedia
The Sevier orogeny was a mountain-building event that affected western North America
from Canada to the north to Mexico to the south. This orogeny was the result of convergent boundary
tectonic activity between approximately 140 million years (Ma) ago and 50 Ma. The Sevier River
area of central Utah
is the namesake of this event. This orogeny
was produced 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 in the Sevier region which caused folding and thrusting. The mountains that were formed as a result were located in western Utah
and eastern Nevada
. The size, shape, and depth of the thrust faults created in the Sevier event are determined by seismic studies and deep well data because they are mostly still buried by overlying rock and sediment. The Sevier and Laramide orogenies ended when subduction along the western edge of North America was overcome by western extension of the North American Plate to start the Basin and Range
Orogeny. The well known and familiar 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
.
and Mesozoic
sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “thin-skinned
” thrust fault
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 the Late Precambrian during the breakup of the supercontinent Rodinia
or during the Ancestral Rocky Mountains orogeny.
to Mesozoic
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
. 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 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 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 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 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 the most deformed in orogenic events the interior of continental plates can also enjoy deformation. In the Sevier-Laramide orogenic events evidence for interior plate deformation includes folds, cleavage
and joint fabrics, distorted fossils, persistent faulting, and calcite twinning.
through Eocene
time. The actual age of initiation of the belt is not entirely agreed upon by researchers. The beginning of deformation in the earliest stages of the orogeny started about 120-80 Ma (millions of years ago) with the formation and continuation of a magmatic arc and foreland fold-thrust belt. However, data from the southern portion of the belt shows contraction in southern Nevada
and southeastern California
beginning about 200 to 92 Ma largely based on intrusions and the formation of the Lavinia Wash conglomerate
sequence due to mountain building and erosion. This deformation continued and intensified around 105 to 100 Ma caused by the continued subduction of the Farallon plate beneath the North American plate. Deformation spread eastward starting around 80 to 75 Ma. 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 to 70 Ma in the present Great Basin
region.
. Mapping Sevier thrusting in 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 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 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 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.
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 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.
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.
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 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 the North American plate.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
from Canada to the north to Mexico to the south. This orogeny was the result of convergent boundary
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
tectonic activity between approximately 140 million years (Ma) ago and 50 Ma. The Sevier River
Sevier River
The Sevier River , extending , is the longest Utah river entirely in the state and drains an extended chain of mountain farming valleys to the intermittent Sevier Lake...
area of central Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
is the namesake of this event. This orogeny
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
was produced by the subduction of the oceanic Farallon Plate
Farallon Plate
The Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate— then located in modern Utah— as Pangaea broke apart during the Jurassic Period...
underneath the continental North American Plate
North American Plate
The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...
. Crustal thickening that led to mountain building was caused by a combination of compressive forces and conductive heating initiated by subduction in the Sevier region which caused folding and thrusting. The mountains that were formed as a result were located in western Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
and eastern Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
. The size, shape, and depth of the thrust faults created in the Sevier event are determined by seismic studies and deep well data because they are mostly still buried by overlying rock and sediment. The Sevier and Laramide orogenies ended when subduction along the western edge of North America was overcome by western extension of the North American Plate to start the Basin and Range
Basin and Range
The Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
Orogeny. The well known and familiar 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
Nevadan orogeny
The Nevadan Orogeny was a major mountain building event that took place along the western edge of ancient North America between the Mid to Late Jurassic...
, the Sonoman orogeny
Sonomia Terrane
The Sonomia Terrane is a geologic crustal block known as a "terrane" whose remnants today lie in northwest Nevada. The terrane acquired its name from the Sonoma Range in that region. The Sonoma Terrane is associated with the Golconda Thrust, a formation named for its proximity to the town of...
, and the Antler orogeny
Antler orogeny
The Antler orogeny is a mountain-building episode that is named for Antler Peak, at Battle Mountain, Nevada. The orogeny extensively deformed Paleozoic rocks of the Great Basin in Nevada and western Utah during Late Devonian and Early Mississippian time...
, and partially overlapped in time and space with the Laramide orogeny
Laramide orogeny
The Laramide orogeny was a 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 orogeny are in dispute, as is the cause. The Laramide...
.
Sevier or Laramide?
Since the Sevier and Laramide orogenies occurred at similar times and places, they are sometimes confused. In general the Sevier orogeny defines a more western compressional event that took advantage of weak bedding planes in overlying PaleozoicPaleozoic
The Paleozoic era is the earliest of three geologic eras of the Phanerozoic eon, spanning from roughly...
and Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
sedimentary rock. As the crust was shortened, pressure was transferred eastward along the weak sedimentary layers, producing “thin-skinned
Thin-skinned deformation
Thin-skinned deformation is a style of deformation in plate tectonics at a convergent boundary which occurs with shallow thrust faults that only involves cover rocks , and not deeper basement rocks....
” thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
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 the Late Precambrian during the breakup of the supercontinent Rodinia
Rodinia
In geology, Rodinia is the name of a supercontinent, a continent which contained most or all of Earth's landmass. According to plate tectonic reconstructions, Rodinia existed between 1.1 billion and 750 million years ago, in the Neoproterozoic era...
or during the Ancestral Rocky Mountains 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. These thin skinned thrusts moved late PrecambrianPrecambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
to Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
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
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. 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
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
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, Utah
Delta is a city in Millard County, Utah, United States. The population was 3,209 at the 2000 census.-Geography:Delta is located at ....
. 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
The Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
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.
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 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, Nevada
Las Vegas is the most populous city in the U.S. state of Nevada and is also the county seat of Clark County, Nevada. Las Vegas is an internationally renowned major resort city for gambling, shopping, and fine dining. The city bills itself as The Entertainment Capital of the World, and is famous...
. 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 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 the most deformed in orogenic events the interior of continental plates can also enjoy deformation. In the Sevier-Laramide orogenic events evidence for interior plate deformation includes folds, cleavage
Cleavage
Cleavage may refer to:*Cleavage , partial exposure of the separation between a woman's breasts.**Cleavage enhancement, methods of making a person's breast cleavage look more substantial than it really is....
and joint fabrics, distorted fossils, persistent faulting, and calcite twinning.
How and when
The Sevier fold and thrust belt was active between late JurassicJurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
through Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
time. The actual age of initiation of the belt is not entirely agreed upon by researchers. The beginning of deformation in the earliest stages of the orogeny started about 120-80 Ma (millions of years ago) with the formation and continuation of a magmatic arc and foreland fold-thrust belt. However, data from the southern portion of the belt shows contraction in southern Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
and southeastern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
beginning about 200 to 92 Ma largely based on intrusions and the formation of the Lavinia Wash conglomerate
Conglomerate (geology)
A conglomerate is a rock consisting of individual clasts within a finer-grained matrix that have become cemented together. Conglomerates are sedimentary rocks consisting of rounded fragments and are thus differentiated from breccias, which consist of angular clasts...
sequence due to mountain building and erosion. This deformation continued and intensified around 105 to 100 Ma caused by the continued subduction of the Farallon plate beneath the North American plate. Deformation spread eastward starting around 80 to 75 Ma. At this time the elevated crust ran into the Colorado Plateau
Colorado Plateau
The Colorado Plateau, also called the Colorado Plateau Province, is a physiographic region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. The province covers an area of 337,000 km2 within western Colorado, northwestern New Mexico,...
. The collision resulted in lateral spreading of deformation and led to a weakened lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
and crustal thickening. Metamorphism
Metamorphism
Metamorphism is the solid-state recrystallization of pre-existing rocks due to changes in physical and chemical conditions, primarily heat, pressure, and the introduction of chemically active fluids. Mineralogical, chemical and crystallographic changes can occur during this process...
due to the crustal heating and thickening is prevalent between 90 to 70 Ma in the present Great Basin
Great Basin
The Great Basin is the largest area of contiguous endorheic watersheds in North America and is noted for its arid conditions and Basin and Range topography that varies from the North American low point at Badwater Basin to the highest point of the contiguous United States, less than away at the...
region.
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 Laramide orogenyLaramide orogeny
The Laramide orogeny was a 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 orogeny are in dispute, as is the cause. The Laramide...
. Mapping Sevier thrusting in the Basin and Range
Basin and Range
The Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
province 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
American Fork Canyon is a canyon located in the Wasatch Mountains of Utah. The canyon is famous for the Timpanogos Cave National Monument, which resides on its south side...
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
Basin and Range
The Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
province extending across Nevada
Nevada
Nevada is a state in the western, mountain west, and southwestern regions of the United States. With an area of and a population of about 2.7 million, it is the 7th-largest and 35th-most populous state. Over two-thirds of Nevada's people live in the Las Vegas metropolitan area, which contains its...
, into western Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, and south into Mexico
Mexico
The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
now consists of N-S normal faulting due to crustal extension. If these normal faults show any extension in late Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
to early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
, 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. 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 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 thrust. The Gass Peak thrust is located in the Las Vegas RangeLas 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.-Description:...
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
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
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, isotopicIsotopic
The word isotopic has a number of different meanings, including:* In the physical sciences, to do with chemical isotopes;* In mathematics, to do with a relation called isotopy.* In geometry, isotopic refers to facet-transitivity....
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 stressDifferential 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
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
. 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
Minnesota is a U.S. state located in the Midwestern United States. The twelfth largest state of the U.S., it is the twenty-first most populous, with 5.3 million residents. Minnesota was carved out of the eastern half of the Minnesota Territory and admitted to the Union as the thirty-second state...
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.
See also
- Geology of the Rocky MountainsGeology of the Rocky MountainsThe 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 Canada through central New Mexico and which is part of the great mountain system known as...
- Basin and RangeBasin and RangeThe Basin and Range Province is a vast physiographic region defined by a unique topographic expression. Basin and Range topography is characterized by abrupt changes in elevation, alternating between narrow faulted mountain chains and flat arid valleys or basins...
- thrust faults
- Laramide OrogenyLaramide orogenyThe Laramide orogeny was a 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 orogeny are in dispute, as is the cause. The Laramide...