Wyoming craton - AbsoluteAstronomy.com

The Wyoming craton is a 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...

located in the west-central United States

United States

The United States of America is a federal constitutional republic comprising fifty states and a federal district...

and western Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

– more specifically, in Montana

Montana

Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...

, Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

, southern Alberta

Alberta

Alberta is a province of Canada. It had an estimated population of 3.7 million in 2010 making it the most populous of Canada's three prairie provinces...

, southern Saskatchewan

Saskatchewan

Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....

, and parts of northern 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...

. Also called the Wyoming province, it is the initial core of the continental crust

Continental crust

The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...

of North America

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...

.

The Wyoming craton was sutured

Suture (geology)

In structural geology, a suture is a major fault zone through an orogen or mountain range. Sutures separate terranes, tectonic units that have different plate tectonic, metamorphic and paleogeographic histories...

together with the Superior

Superior craton

The Superior craton forms the core of the Canadian Shield at the heart of the North American continent. It extends from Quebec in the east to eastern Manitoba in the west...

and Hearne-Rae

Rae craton

right|thumb|250px|North America cratons and basement rock.The Rae craton is an Archean craton located in northern Canada north of the Superior craton.-Ungava Peninsula:...

cratons in the mountain-building episode

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...

that created the Trans-Hudson Suture Zone

Trans-Hudson orogeny

The Trans-Hudson orogeny, Trans-Hudsonian orogeny, Trans-Hudson orogen , or Trans-Hudson Orogen Transect , , was the major mountain building event that formed the Precambrian Canadian Shield, the North American craton , and the...

to form the core of North America (Laurentia

Laurentia

Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

). It was incorporated into southwest Laurentia approximately 1.86 billion years ago.

Local preservation of 3.6–3.0 Ga gneiss

Gneiss

Gneiss is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from pre-existing formations that were originally either igneous or sedimentary rocks.-Etymology:...

es and widespread isotopic

Isotope

Isotopes are variants of atoms of a particular chemical element, which have differing numbers of neutrons. Atoms of a particular element by definition must contain the same number of protons but may have a distinct number of neutrons which differs from atom to atom, without changing the designation...

evidence for crust of this age incorporated into younger plutons indicates that the Wyoming craton was, and still is, a 100,000 km² middle Archean

Archean

The Archean , also spelled Archeozoic or Archæozoic) is a geologic eon before the Paleoproterozoic Era of the Proterozoic Eon, before 2.5 Ga ago. Instead of being based on stratigraphy, this date is defined chronometrically...

craton that was modified by late Archean magmatism and tectonism and Proterozoic

Proterozoic

The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...

extension and rifting.

The Wyoming, Superior and Hearne cratons were once sections of separate continent

Continent

A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...

s, but today they are all welded together. The collision of these cratons began before ca. 1.77 Ga, with post-tectonic magmatism

Magmatism

The formation of igneous rocks from magma is known as Magmatism.Magmatism is a process responsible for mountain formation. The process of magmatism produces an additional mass and volume to the Earth’s surface. For example the formation of volcanoes or island arcs at convergent plate boundaries...

at ca. 1.715 Ga (the Harney Peak

Harney Peak

Harney Peak is the highest natural point in South Dakota. Harney Peak is located within the Black Elk Wilderness area, in southern Pennington County, within Black Hills National Forest...

granite

Granite

Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...

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

Trans-Hudson orogeny

in Canada

Canada

.

Younger metamorphic

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...

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

The Dakotas

The Dakotas is a collective term that refers to the U.S. states of North Dakota and South Dakota together. The term has been used historically to describe the Dakota Territory, and is continued to be used to describe the collective heritage, culture, geography, fauna, sociology, the economy, and...

and southeastern Montana

Montana

. The final assembly of the eastern Wyoming craton with Laurentia

Laurentia

Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

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

Volcanic arc

A volcanic arc is a chain of volcanoes positioned in an arc shape as seen from above. Offshore volcanoes form islands, resulting in a volcanic island arc. Generally they result from the subduction of an oceanic tectonic plate under another tectonic plate, and often parallel an oceanic trench...

accretion

Accretion (geology)

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.-Description:...

along the southern margin of the growing craton.

Geologic summary

The Precambrian

Precambrian

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...

basement of Wyoming consists mainly of three major geologic terrane

Terrane

A terrane in geology is short-hand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or "sutured" to crust lying on another plate...

s, the Archean

Archean

Wyoming craton (province), the Paleoproterozoic

Paleoproterozoic

The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...

Trans-Hudson orogen, and the Paleoproterozoic Colorado orogeny

Colorado orogeny

The Colorado orogeny, or Colorado orogen, was an orogeny in Colorado and surrounding areas which was a part of the development of the ancestral Rockies...

. 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

Pluton

A pluton in geology is a body of intrusive igneous rock that crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies...

s (2.8–2.55 Ga) and gneiss

Gneiss

and migmatite

Migmatite

Migmatite is a rock at the frontier between igneous and metamorphic rocks. They can also be known as diatexite.Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally...

—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 Wyoming province 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

Detrital

Detritus is a geological term used to describe particles of rock derived from pre-existing rock through processes of weathering and erosion. Detrital particles can consist of lithic fragments , or of monomineralic fragments...

zircon

Zircon

Zircon is a mineral belonging to the group of nesosilicates. Its chemical name is zirconium silicate and its corresponding chemical formula is ZrSiO4. A common empirical formula showing some of the range of substitution in zircon is 1–x4x–y...

ages up to 4.0 Ga, and Nd model ages exceeding 4.0 Ga); (2) a distinctly enriched 207Pb

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

/204Pb isotopic

Isotope

signature, which suggests that this part of the province was not produced by the amalgamation of exotic terranes; and (3) a distinctively thick (15–20 km), mafic

Mafic

Mafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...

lower crust. The Montana metasedimentary province and Beartooth-Bighorn magmatic zone were cratonized by about 3.0–2.8 Ga. Crustal growth occurred via continental-arc magmatism and 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.

In another analysis by Chamberlain (2003), on basis of differences in late Archean histories, the Wyoming Province is subdivided 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 be 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 tectonic grain that was established by three or more temporally related, 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 Laramide uplifts. 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. 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 Paleoproterozoic

Paleoproterozoic

The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...

the Colorado orogeny

Colorado orogeny

The Colorado orogeny, or Colorado orogen, was an orogeny in Colorado and surrounding areas which was a part of the development of the ancestral Rockies...

accreted to the Wyoming craton along the Cheyenne belt

Cheyenne belt

The Cheyenne Belt is the tectonic suture zone between the Archean-age Wyoming craton to the north and the Paleoproterozoic-age Yavapai province to the south. In runs through the southeastern quadrant of the state of Wyoming, USA. It was formed during the Paleoproterozoic Medicine Bow orogeny...

, a 500-km-wide belt of Proterozoic island-arc rocks named for Cheyenne, Wyoming. As a result of the collision, Archean rocks of the Wyoming province were intensely deformed and metamorphosed for at least 75 km inboard from the suture marked by the Laramie Mountains. Collision along the east margin of the craton with the Paleoproterozoic Trans-Hudson orogen intensely deformed Archean cratonic rocks in the Hartville uplift and the Laramie Mountains.

Mesoproterozoic (~1.4 Ga) anorthosite

Anorthosite

Anorthosite is a phaneritic, intrusive igneous rock characterized by a predominance of plagioclase feldspar , and a minimal mafic component...

and syenite

Syenite

Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or present in relatively small amounts Syenite is a coarse-grained intrusive igneous rock of the same general composition as granite but with the quartz either absent or...

s of the Laramie Anorthosite Complex and granite (ilmenite

Ilmenite

Ilmenite is a weakly magnetic titanium-iron oxide mineral which is iron-black or steel-gray. It is a crystalline iron titanium oxide . It crystallizes in the trigonal system, and it has the same crystal structure as corundum and hematite....

-bearing Sherman Granite) intrude rocks of the Colorado orogen in the Laramie and adjacent Medicine Bow Mountains

Medicine Bow Mountains

The Medicine Bow Mountains are a mountain range in the Rocky Mountains that extend for from northern Colorado into southern Wyoming. The northern extent of this range is the sub-range the Snowy Range...

. 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.

The Wyoming craton owes its spectacular mountainous terranes mainly to a regional episode of compressional deformation during the Laramide orogeny (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 present-day topography. Vertical displacement of the basement surface was as much as 30,000 ft. (9250 m). By contrast, Sevier-aged

Sevier orogeny

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 ago and 50 Ma. The Sevier River area of central Utah...

thrusting

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...

, of approximately the same age, in western Wyoming 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. High-angle faulting of Pliocene

Pliocene

The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...

-Pleistocene

Pleistocene

The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

age formed the Teton Range

Teton Range

The Teton Range is a mountain range of the Rocky Mountains in North America. A north-south range, it is on the Wyoming side of the state's border with Idaho, just south of Yellowstone National Park. Most of the range is in Grand Teton National Park....

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

Geologic summary

Wyoming province subdivisions

Accretion events

See also