The Colorado orogeny was an episode of

mountain building Mountain formation occurs due to a variety of geological processes associated with large-scale movements of the Earth's crust (List of tectonic plates, tectonic plates). Fold (geology), Folding, Fault (geology), faulting, Volcano, volcanic acti ...

(an ''

orogeny Orogeny () is a mountain-mountain formation, building process that takes place at a convergent boundary, convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is tectonic uplift, u ...

'') in

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

and surrounding areas. This took place from 1780 to 1650 million years ago ( Mya), during the

Paleoproterozoic The Paleoproterozoic Era (also spelled Palaeoproterozoic) is the first of the three sub-divisions ( eras) of the Proterozoic eon, and also the longest era of the Earth's geological history, spanning from (2.5–1.6 Ga). It is further sub ...

(

Statherian The Statherian Period (; , meaning "stable, firm") is the final geologic period in the Paleoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. Th ...

Period). It is recorded in the Colorado orogen, a >500-km-wide belt of

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

ic arc rock that extends southward into

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. The Colorado orogeny was likely part of the larger

Yavapai orogeny The Yavapai orogeny was an orogenic (mountain-building) event in what is now the Southwestern United States that occurred between 1710 and 1680 million years ago ( Mya), in the Statherian Period of the Paleoproterozoic. Recorded in the rocks o ...

Description

The Colorado orogen, formerly called the Colorado

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

, is a >500-km-wide belt of

ic arc rock (1.78–1.65 Ga) that extends southward into

and composes a major part of the

Proterozoic The Proterozoic ( ) is the third of the four geologic eons of Earth's history, spanning the time interval from 2500 to 538.8 Mya, and is the longest eon of Earth's geologic time scale. It is preceded by the Archean and followed by the Phanerozo ...

provinces of

southwestern United States The Southwestern United States, also known as the American Southwest or simply the Southwest, is a geographic and cultural list of regions of the United States, region of the United States that includes Arizona and New Mexico, along with adjacen ...

. This transcontinental collisional event occurred during the

(

Period).http://pubs.usgs.gov/of/2001/ofr-01-0364/colo_of_text.html#Co_orogeny USGS Open-File Report 01-0364: Preliminary Precambrian Basement Map of Colorado The

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

sector of the Colorado orogeny was formerly called the Medicine Bow orogeny. The eastern sector extends into the High Plains and is called the Central Plains orogeny. The boundary between the Colorado orogeny and the

Wyoming craton The Wyoming Craton is a craton in the west-central United States and western Canada – more specifically, in Montana, Wyoming, southern Alberta, southern Saskatchewan, and parts of northern Utah. Also called the Wyoming Province, it is the init ...

is the

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. It runs through the southeastern quadrant of the state of Wyoming, United States. It was f ...

, a 5-km-wide mylonitic

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...

that verges northward. The Cheyenne belt transects and cuts off the south edge of the older

Trans-Hudson orogeny The Trans-Hudson orogeny or Trans-Hudsonian orogeny was the major mountain building event (orogeny) that formed the Precambrian Canadian Shield and the North American Craton (also called Laurentia), forging the initial North American conti ...

. The Paleoproterozoic

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

and

sedimentary rocks Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedim ...

that resulted from the Colorado orogeny underwent

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

followed by plastic

folding Fold, folding or foldable may refer to: Arts, entertainment, and media * ''Fold'' (album), the debut release by Australian rock band Epicure * Fold (poker), in the game of poker, to discard one's hand and forfeit interest in the current pot *Abov ...

under moderate pressure and temperature (PT) conditions (temperature about 500 °C and pressures in excess of 1.2

GPa Grading in education is the application of standardized measurements to evaluate different levels of student achievement in a course. Grades can be expressed as letters (usually A to F), as a range (for example, 1 to 6), percentages, or as num ...

). The metamorphism was accompanied by intrusion of intermediate calc-alkalic rocks, such as the

granodiorite Granodiorite ( ) is a coarse-grained (phaneritic) intrusive igneous rock similar to granite, but containing more plagioclase feldspar than orthoclase feldspar. The term banatite is sometimes used informally for various rocks ranging from gra ...

s of the

Boulder Creek batholith In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In com ...

. The accompanying

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose ...

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...

metamorphism is characterized by

sillimanite Sillimanite or fibrolite is an aluminosilicate mineral with the chemical formula Al2SiO5. Sillimanite is named after the American chemist Benjamin Silliman (1779–1864). It was first described in 1824 for an occurrence in Chester, Connecticut ...

and, locally,

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. Garnet minerals, while sharing similar physical and crystallographic properties, exhibit a wide range of chemical compositions, de ...

andalusite Andalusite is an aluminium nesosilicate mineral with the chemical formula Al2SiO5. This mineral was called andalousite by Delamétherie, who thought it came from Andalusia, Spain. It soon became clear that it was a locality error, and that the sp ...

, and

cordierite Cordierite (mineralogy) or iolite (gemology) is a magnesium iron aluminium cyclosilicate. Iron is almost always present, and a solid solution exists between Mg-rich cordierite and Fe-rich sekaninaite with a series formula: to . A high-tempera ...

. Contemporaneity of emplacement of the granodioritic rocks with folding is indicated by concordant

plutonic Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: Marc ...

boundaries and by conformity of the internal structure (of solid-state recrystallization) in the batholith with that in the

supracrustal Supracrustal rocks (''supra'' (Latin for "above")) are rocks that were deposited on the existing basement rocks of the crust, hence the name. They may be further metamorphosed from both sedimentary Sedimentary rocks are types of rock form ...

wall rocks. Comparable mineral facies in the country rocks and batholiths indicate that emplacement took place at moderate depths. As is typical of large orogenies deformation patterns of the Colorado orogeny differ throughout the range. Adjacent to the Cheyenne belt, and extending across a width of at least 150 km to the south, foliation and upright folds predominantly trend westward. In the northern

Front Range The Front Range is a mountain range of the Southern Rocky Mountains of North America located in the central portion of the U.S. State of Colorado, and southeastern portion of the U.S. State of Wyoming. It is the first mountain range encounter ...

sector of this region, geologic mapping demonstrated three generations of northwest-trending folds that pre-date the ~1.4 Ga shear zones. Similar fold patterns are present in the northern Park Range and

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 Summ ...

. These structural

fabrics Textile is an umbrella term that includes various fiber-based materials, including fibers, yarns, filaments, threads, and different types of fabric. At first, the word "textiles" only referred to woven fabrics. However, weaving is not ...

indicate shortening in a north-south direction and can be explained by collision, subsequent subduction, and continued convergence along the Cheyenne belt. Farther south, more distant from the Cheyenne belt, fold patterns differ materially from those in the northernmost part of the Colorado orogeny. In the north-central Front Range, west of

Denver Denver ( ) is a List of municipalities in Colorado#Consolidated city and county, consolidated city and county, the List of capitals in the United States, capital and List of municipalities in Colorado, most populous city of the U.S. state of ...

, in an area of >2000 km² that has been mapped in detail the older regional folds mainly bear north-northeast; the folds range from broad open, upright folds to tight, upright folds that plunge gently to moderately northeast. In nearby areas to the east and west, however, the folds of the older orogenic event trend northwest; field observations indicate that these folds apparently are slightly older than the more prevalent north-trending folds, but both generations are part of the older

gneiss Gneiss (pronounced ) 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. This rock is formed under p ...

-forming episode inasmuch as they are cut by the Boulder Creek batholith. Both sets of these folds indicate shortening events resulting from regional

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phra ...

patterns. Because of the consistency of these fold patterns over relatively large areas, evidence for folding resulting from forceful

intrusion 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 ...

igneous Igneous rock ( ), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rocks are formed through the cooling and solidification of magma or lava. The magma can be derived from partial ...

rocks is generally lacking; intrusions of this orogenic event are

synkinematic Orogeny () is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involv ...

, as exemplified by the much-studied Boulder Creek batholith. The Colorado orogeny was likely part of the larger

, which extended across North America and probably to other continents that were joined to North America as part of the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

, Columbia.

References

{{reflist Orogenies of North America Paleoproterozoic orogenies Geography of Colorado Geology of Colorado