Aspen anomaly is a geological structure in Colorado, United States. It consists of a low-

seismic velocity A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large man ...

anomaly in the mantle which underpins the highest sector of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in great-circle distance, straight-line distance from the northernmost part of Western Can ...

Characteristics

The Aspen anomaly is a

anomaly in the mantle beneath central

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 ...

(in the region of

Aspen, Colorado Aspen is the List of municipalities in Colorado#Home rule municipality, home rule city that is the county seat and the List of municipalities in Colorado, most populous municipality of Pitkin County, Colorado, United States. The city population ...

), which appears to reach down into the

upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (geology), crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle (Earth), lower man ...

Helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

with

isotope ratio The term stable isotope has a meaning similar to stable nuclide, but is preferably used when speaking of nuclides of a specific element. Hence, the plural form stable isotopes usually refers to isotopes of the same element. The relative abundan ...

s indicative of mantle origin emanates from the terrain above the anomaly. The Aspen anomaly coincides with the highest region of the

(such as the

San Juan Mountains The San Juan Mountains is a high and rugged mountain range in the Rocky Mountains in southwestern Colorado and northwestern New Mexico. The area is highly mineralized (the Colorado Mineral Belt) and figured in the gold and silver mining industry ...

and the

Sawatch Range The Sawatch Range or Saguache RangeThe place name "Saguache” is pronounced “Sawatch” . This name derives from the Ute language noun "''sawup''" meaning "sand dunes" and is spelled using the Spanish language version of this name "Saguach ...

) and divergent

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess water. The internal drainage of most agricultural soils can prevent severe waterlogging (anaerobic conditions that harm root gro ...

s (

Arkansas River The Arkansas River is a major tributary of the Mississippi River. It generally flows to the east and southeast as it traverses the U.S. states of Colorado, Kansas, Oklahoma, and Arkansas. The river's source basin lies in Colorado, specifically ...

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

and

Gunnison River The Gunnison River is located in western Colorado, United States and is one of the largest tributaries of the Colorado River. Description The river flows east to west and has a drainage area of according to the USGS. The drainage basin of the ...

) which have cut deep gorges. This region underwent significant uplift during the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

starting from 10-5 million years ago and was subsequently eroded by the Colorado River. Ongoing present-day uplift of the San Juan Mountains may be linked to the Aspen anomaly. River knickpoints in Gore Canyon and Black Canyon may mark the point at which the rivers pass through the edge of the region above the anomaly. The Colorado River may be influenced by the anomaly all the way to Lees Ferry, Arizona.

Hot spring A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...

s and

geyser A geyser (, ) is a spring with an intermittent water discharge ejected turbulently and accompanied by steam. The formation of geysers is fairly rare and is caused by particular hydrogeological conditions that exist only in a few places on Ea ...

s above the anomaly are a major source of

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

and other gases, some linked to chemolithotrophic bacterial communities.

volcanism is also associated with the anomaly, such as potentially the Twin Lakes

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 ...

close to

Leadville, Colorado Leadville ( ) is a List of municipalities in Colorado#Statutory city, statutory city that is the county seat, the most populous community, and the only List of municipalities in Colorado, incorporated municipality in Lake County, Colorado, Lak ...

Context

In seismic tomography images, the Aspen anomaly is characterized by a northwards tilted low seismic velocity anomaly. The anomaly is one among several low velocity anomalies beneath the western United States, although unlike the others known as the Jemez, Yellowstone and St. George it does not have a northeastward throw. Other structures that may be related to the Aspen anomaly are the Lester Mountain zone, the Colorado mineral belt and the

Rio Grande Rift The Rio Grande rift is a north-trending continental rift zone. It separates the Colorado Plateau in the west from the interior of the North American craton on the east. The rift extends from central Colorado in the north to the state of Chihuah ...

. The Aspen anomaly has been compared with the Yellowstone hotspot, but it lacks a volcanic

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

that Yellowstone has.

Origin

The Aspen anomaly has been interpreted in several ways. * It may be a

mantle plume A mantle plume is a proposed mechanism of convection within the Earth's mantle, hypothesized to explain anomalous volcanism. Because the plume head partially melts on reaching shallow depths, a plume is often invoked as the cause of volcanic ho ...

, but the steep tilt angle is unusual for a mantle plume. * It may be a lithospheric melt zone, but the lithosphere is not thick enough to contain such a structure. * It may be a

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 ...

structure, maybe the leftover of a

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

zone. Prolonged subduction would have enriched a segment of mantle with

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

and thus lowered its

melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature at which it changes state of matter, state from solid to liquid. At the melting point the solid and liquid phase (matter), phase exist in Thermodynamic equilib ...

. * Shallower upwelling (such as asthenospheric upwelling), possibly linked with slab rollback or crustal delamination processes. * Crustal weaknesses.

References

Sources

* * {{refend Geology of Colorado Rocky Mountains