The Wyoming Craton is a

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 ...

in the west-central United States and western Canada – more specifically, in

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

Wyoming Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to t ...

, southern

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...

, southern

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

, and parts of northern

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 its ...

. Also called the Wyoming Province, it is the initial core of the

continental crust Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called '' sial'' be ...

of North America. The Wyoming Craton was sutured together with the

Superior Superior may refer to: *Superior (hierarchy), something which is higher in a hierarchical structure of any kind Places *Superior (proposed U.S. state), an unsuccessful proposal for the Upper Peninsula of Michigan to form a separate state *Lake ...

and Hearne- Rae cratons in the mountain-building episode that created the Trans-Hudson Suture Zone to form the core of North America (

Laurentia Laurentia or the North American Craton is a large continental craton that forms the ancient geological core of North America. Many times in its past, Laurentia has been a separate continent, as it is now in the form of North America, althoug ...

). It was incorporated into southwest Laurentia approximately 1.86 billion years ago. Local preservation of 3.6–3.0 Ga

gneiss Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. Gneiss forms at higher temperatures a ...

es and widespread isotopic evidence for crust of this age incorporated into younger plutons indicates that the Wyoming Craton originated as a 100,000 km² middle

Archean The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic. The Earth during the Arc ...

craton that was modified by late Archean volcanic magmatism and plate movements and

Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 538.8million years ago. It is the most recent part of the Precambrian "supereon". It is also the longest eon of the Earth's geologic time scale, and it is subdivided i ...

extension and

rift 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-grabe ...

ing. The Wyoming, Superior and Hearne-Ray cratons were once sections of separate continents, but today they are all welded together. The collisions of these cratons began before ca. 1.77 Ga, with post-

tectonic Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents ...

magmatism Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...

at ca. 1.715 Ga (the

Harney Peak Black Elk Peak is the highest natural point in the U.S. state of South Dakota and the Midwestern United States. It lies in the Black Elk Wilderness area, in southern Pennington County, in the Black Hills National Forest. The peak lies west-sou ...

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...

). This tectonic-magmatic interval is 50–60 million years younger than that reported for the Hearne-Superior collision of the Trans-Hudson orogeny in Canada. Younger

metamorphic Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

dates (1.81–1.71 Ga) also typify the eastern and northern Wyoming province peripheries in the western

Dakotas The Dakotas is a collective term for the U.S. states of North Dakota and South Dakota. It has been used historically to describe the Dakota Territory, and is still used for the collective heritage, culture, geography, fauna, sociology, econo ...

and southeastern

. The final assembly of the eastern Wyoming Craton as part of the continent

began during the ca. 1.78–1.74 Ga interval of island-arc

accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...

along the southern margin of the growing craton.

Geologic summary

The

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 th ...

basement of Wyoming consists mainly of three major geologic

terrane In geology, a terrane (; in full, a tectonostratigraphic terrane) is a crust fragment formed on a tectonic plate (or broken off from it) and accreted or " sutured" to crust lying on another plate. The crustal block or fragment preserves its ow ...

s, the

Wyoming Craton or Province, the

Paleoproterozoic The Paleoproterozoic Era (;, also spelled Palaeoproterozoic), spanning the time period from (2.5–1.6 Ga), is the first of the three sub-divisions ( eras) of the Proterozoic Eon. The Paleoproterozoic is also the longest era of the Earth's ...

Trans-Hudson orogen, and the Paleoproterozoic

Colorado orogeny The Colorado orogeny was an episode of mountain building (an ''orogeny'') in Colorado and surrounding areas. This took place from 1780 to 1650 million years ago ( Mya), during the Paleoproterozoic (Statherian Period). It is recorded in the Colorado ...

. The Colorado orogen collided with the Wyoming Craton at 1.78–1.75 Ga. Collision of the Colorado orogen and the Trans-Hudson orogen with the Archean craton produced strong structural overprinting along the southern and eastern margins of the Wyoming craton. The Wyoming Craton consists mainly of two gross rock units—granitoid

pluton In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s (2.8–2.55 Ga) and

and

migmatite Migmatite is a composite rock found in medium and high-grade metamorphic environments, commonly within Precambrian cratonic blocks. It consists of two or more constituents often layered repetitively: one layer is an older metamorphic rock th ...

—together with subordinate (<10 percent) supracrustal metavolcanic-metasedimentary rocks. The granitoid rocks are mainly potassic granite and were derived principally from reworked older (3.1–2.8 Ga) gneiss. Magnetic contrast between the granitoid rocks and gneiss provides a means to map these gross rock units in covered areas. The overall structural pattern of the Archean units shown by magnetic data is crudely semi-circular and open to the north.

Wyoming province subdivisions

The present-day lithospheric architecture of the Wyoming Province is the result of cumulative processes of crustal growth, tectonic modification, and lithospheric contrasts that have apparently persisted for billions of years. The Wyoming

province A province is almost always an administrative division within a country or state. The term derives from the ancient Roman ''provincia'', which was the major territorial and administrative unit of the Roman Empire's territorial possessions out ...

can be subdivided into three subprovinces, namely, from oldest to youngest, the Montana metasedimentary province, the Beartooth–Bighorn magmatic zone, and the Southern accreted terranes. Archean rocks of the Montana metasedimentary province and the Beartooth-Bighorn magmatic zone are characterized by (1) their antiquity (rock ages to 3.5 Ga, detrital

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of t ...

ages up to 4.0 Ga, and Nd model ages exceeding 4.0 Ga); (2) a distinctly enriched ²⁰⁷Pb/ ²⁰⁴Pb isotopic signature, which suggests that this part of the province was not produced by the amalgamation of already-formed exotic terranes; and (3) a distinctively thick (15–20 km),

mafic A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks in ...

lower crust. The Montana metasedimentary province and Beartooth–Bighorn magmatic zone were established as cratons by about 3.0–2.8 Ga. Crustal growth occurred through a combination of continental-arc magmatism resulting from oceanic crust subducted beneath continental crust on an adjacent plate, creating an arc-shaped mountain belt, together with terrane accretion in the Southern accreted terranes along the southern margin of the province at 2.68–2.50 Ga. By the end of the Archean, the three subprovinces were joined as part of what is now the Wyoming craton. Subsequent to amalgamation of the Wyoming crust to Laurentia at ca. 1.8–1.9 Ga, Paleoproterozoic crust (1.7–2.4 Ga) was juxtaposed along the southern and western boundaries of the province. Subsequent tectonism and magmatism in the Wyoming region are concentrated in the areas underlain by these Proterozoic mobile belts. An analysis by Kevin Chamberlain ''et al.'' (2003), on the basis of differences in late Archean histories, subdivides the Wyoming Province into five subprovinces: three in the Archean core, (1) the Montana metasedimentary province, (2) the Bighorn subprovince, and (3) the Sweetwater subprovince, and two Archean terrains that may have originated elsewhere (that is, allochthonous to the 3.0 Ga craton), (4) the Sierra Madre – Medicine Bow block, and (5) the Black Hills – Hartville block. Based on imaging by the "Deep Probe" analysis, a thick lower crustal layer corresponds geographically with the Bighorn subprovince and may be an underplate associated with ca. 2.70 Ga mafic magmatism. The Sweetwater subprovince is characterized by an east–west-tending tectonic grain that was established by three or more roughly contemporaneous late Archean, pulses of basin development, shortening, and arc magmatism. This tectonic grain, including the 2.62 Ga Oregon Trail structure, controlled the locations and orientations of Proterozoic rifting and uplifts related to 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 ...

. If there has been any net crustal growth of the Wyoming Province since 3.0 Ga, it has involved a combination of mafic underplating and arc magmatism.

Accretion events

During the

, island-arc terrane associated with the

accreted to the Wyoming Craton along the Cheyenne belt, a 500-km-wide belt of Proterozoic rocks named for

Cheyenne, Wyoming Cheyenne ( or ) is the capital and most populous city of the U.S. state of Wyoming, as well as the county seat of Laramie County, with 65,132 residents, per the 2020 US Census. It is the principal city of the Cheyenne metropolitan statistic ...

. As a result of the collision, older, Archean rocks of the Wyoming province were intensely deformed and metamorphosed for at least 75 km inboard from the suture, which is marked today by the Laramie Mountains. Along the east margin of the craton, collision with the Paleoproterozoic Trans-Hudson orogen intensely deformed Archean cratonic rocks in the Hartville uplift. Mesoproterozoic (~1.4 Ga)

anorthosite Anorthosite () is a phaneritic, intrusive igneous rock characterized by its composition: mostly plagioclase feldspar (90–100%), with a minimal mafic component (0–10%). Pyroxene, ilmenite, magnetite, and olivine are the mafic minerals most ...

and

syenite Syenite is a coarse-grained intrusive igneous rock with a general composition similar to that of granite, but deficient in quartz, which, if present at all, occurs in relatively small concentrations (< 5%). Some syenites contain larger prop ...

s of the Laramie Anorthosite Complex and granite (

ilmenite Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...

-bearing Sherman Granite) intrude into rocks of the Colorado orogen in the Laramie and adjacent

Medicine Bow Mountains The Medicine Bow Mountains are a mountain range in the Rocky Mountains that extend from northern Colorado into southern Wyoming. The northern extent of this range is the sub-range the Snowy Range. From the northern end of Colorado's Never Summe ...

. Both the anorthosite and granite transect the Cheyenne belt in the Laramide Mountains, and intrude crystalline rocks of the Wyoming province. These intrusions comprise the northernmost segment of a wide belt of 1.4 Ga granitic intrusions that occur throughout the Colorado orogen. Long after its assembly, the Wyoming Craton owes its spectacular mountainous terranes mainly to a regional episode of compressional deformation during the

(ca.60 Ma). The basement blocks composed of Precambrian rocks were uplifted locally to high levels in the crust during the deformation, and subsequent erosion has molded the uplifted rocks into the rugged present-day topography. Vertical displacement of the basement surface was as much as 30,000 ft. (9250 m). By contrast, in western Wyoming

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 ...

ing, associated with the

Sevier orogeny The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south. The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred fr ...

of approximately the same age, was thin-skinned, and the lack of disruption of magnetic anomalies in the region indicates that the basement rocks were little disturbed and not significantly uplifted during the thrusting. Even younger high-angle faulting of

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological Epoch (geology), epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was fina ...

age has formed the

Teton Range The Teton Range is a mountain range of the Rocky Mountains in North America. It extends for approximately in a north–south direction through the U.S. state of Wyoming, east of the Idaho state line. It is south of Yellowstone National Park and ...

. Vertical relief on the east face of the mountains is about 25,000 ft. (7800 m).

References

{{DEFAULTSORT:Wyoming Craton Cratons Proterozoic geology Proterozoic North America Geology of North America Precambrian Canada Precambrian United States Geology of Wyoming Geology of Montana Geology of Alberta Geology of Saskatchewan Geology of Utah Geology of the United States

Geologic summary

Wyoming province subdivisions

Accretion events

See also

References