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The Rio Grande rift is a north-trending continental
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 ...
zone. It separates the Colorado Plateau in the west from the interior of the North American
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 an ...
on the east. The rift extends from central
Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...
in the north to the state of Chihuahua,
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
, in the south. The rift zone consists of four basins that have an average width of . The rift can be observed on location at
Rio Grande National Forest Rio Grande National Forest is a 1.86 million-acre (7,530 km²) U.S. National Forest located in southwestern Colorado. The forest encompasses the San Luis Valley, which is the world's largest agricultural alpine valley, as well as one of ...
, White Sands National Park,
Santa Fe National Forest The Santa Fe National Forest is a protected United States National Forest, national forest in northern New Mexico in the Southwestern United States. It was established in 1915 and covers . Elevations range from 5,300 feet (1600 m) to 13,103 ...
, and
Cibola National Forest The Cibola National Forest (pronounced SEE-bo-lah) is a 1,633,783 acre (6,611.7 km2) United States National Forest in New Mexico, USA. The name Cibola is thought to be the original Zuni Indian name for their pueblos or tribal lands. The name w ...
, among other locations. The Rio Grande rift has been an important site for humans for a long time, because it provides a north–south route that follows a major river. The
Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...
follows the course of the rift from southern Colorado to El Paso, where it turns southeast and flows toward the
Gulf of Mexico The Gulf of Mexico ( es, Golfo de México) is an oceanic basin, ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of ...
. Important cities, including
Albuquerque Albuquerque ( ; ), ; kee, Arawageeki; tow, Vakêêke; zun, Alo:ke:k'ya; apj, Gołgéeki'yé. abbreviated ABQ, is the most populous city in the U.S. state of New Mexico. Its nicknames, The Duke City and Burque, both reference its founding in ...
, Santa Fe,
Taos Taos or TAOS may refer to: Places * Taos, Missouri, a city in Cole County, Missouri, United States * Taos County, New Mexico, United States ** Taos, New Mexico, a city, the county seat of Taos County, New Mexico *** Taos art colony, an art colo ...
, Española, Las Cruces,
El Paso El Paso (; "the pass") is a city in and the seat of El Paso County in the western corner of the U.S. state of Texas. The 2020 population of the city from the U.S. Census Bureau was 678,815, making it the 23rd-largest city in the U.S., the s ...
, and
Ciudad Juárez Ciudad Juárez ( ; ''Juarez City''. ) is the most populous city in the Mexican state of Chihuahua. It is commonly referred to as Juárez and was known as El Paso del Norte (''The Pass of the North'') until 1888. Juárez is the seat of the Ju ...
, lie within the rift.


Geology

The Rio Grande rift represents the easternmost manifestation of widespread extension in the western U.S. during the past 35 million years. The rift consists of three major basins and many smaller basins, less than . The three major basins (from northernmost to southernmost) are the San Luis, Española, and
Albuquerque Albuquerque ( ; ), ; kee, Arawageeki; tow, Vakêêke; zun, Alo:ke:k'ya; apj, Gołgéeki'yé. abbreviated ABQ, is the most populous city in the U.S. state of New Mexico. Its nicknames, The Duke City and Burque, both reference its founding in ...
basins. The rift's northern extent is delineated by the upper Arkansas River basin between
Leadville The City of Leadville is a statutory city that is the county seat, the most populous community, and the only incorporated municipality in Lake County, Colorado, United States. The city population was 2,602 at the 2010 census and an estimated ...
and
Salida, Colorado The City of Salida ( ; Spanish: , "exit") is the Statutory city that is the county seat and the most populous municipality of Chaffee County, Colorado, United States. The population was 5,666 at the 2020 census. History A post office has bee ...
. Further south, the rift is defined by a network of smaller, less topographically distinct alternating basins and ranges. The distinction between these smaller basins and those of the
Basin and Range Province The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...
becomes blurred in northern
Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...
. Basin size generally decreases to the north in the rift, though the Española covers approximately north–south and east–west, and the San Luis is roughly . These basins may contain smaller units within them, such as the
Alamosa Alamosa is a home rule municipality and the county seat of Alamosa County, Colorado, United States. The city population was 9,806 at the 2020 United States Census. The city is the commercial center of the San Luis Valley in south-central Colora ...
basin within the San Luis, which is bounded by the San Juan and Tusas mountains on the west and the
Sangre de Cristo Mountains ) , country= United States , subdivision1_type= States , subdivision1= , parent= Rocky Mountains , geology= , orogeny= , area_mi2= 17193 , range_coordinates= , length_mi= 242 , length_orientation= north-south , width_mi= 120 , w ...
in the east. The Albuquerque basin is the largest of the three basins, spanning north–south and east–west at its widest points. It is the oldest of the three major basins, and contains of
Paleogene The Paleogene ( ; British English, also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period, geologic period and system that spans 43 million years from the end of the Cretaceous Period million yea ...
clastic
sediments Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand a ...
deposited on
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 the ...
basement. The southernmost Albuquerque basin contains pre-rift volcanic deposits, while the central and northern portions contain volcanics erupted during rifting. In cross-section, the geometry of the basins within the rift are asymmetrical half-grabens, with major fault boundaries on one side and a downward hinge on the other. Which side of the basin has the major fault or the hinge alternates along the rift. The alternation between these half-grabens occurs along transfer faults, which trend across the rift to connect the major basin-bounding faults and occur between basins or, in places, within basins. The Precambrian basement changes relief sharply in this area, from below sea level at the bottom of the Albuquerque basin to above sea level in the nearby
Sandia Mountains The Sandia Mountains (Southern Tiwa: ''Posu gai hoo-oo'', Keres: ''Tsepe,'' Navajo: ''Dził Nááyisí''; Tewa: ''O:ku:p’į'', Northern Tiwa: ''Kep’íanenemą''; Towa: ''Kiutawe'', Zuni: ''Chibiya Yalanne'') are a mountain range located in ...
, which flanks the Albuquerque basin to the east. Flanking mountains are generally taller along the east side of the rift (although some of this relief may be
Laramide 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 th ...
in origin). The thickness of the crust increases to the north beneath the rift, where it may be as much as thicker than it is in the south. The crustal thickness underneath the rift is on average , thinner by than the Colorado Plateau on the west and the Great Plains to the east. Formation of the rift began with significant deformation and faulting with offsets of many kilometers starting about 35 Ma. The largest-scale manifestation of rifting involves a pure-shear rifting mechanism, in which both sides of the rift pull apart evenly and slowly, with the lower crust and
upper mantle The upper mantle of Earth is a very thick layer of rock inside the planet, which begins just beneath the crust (at about under the oceans and about under the continents) and ends at the top of the lower mantle at . Temperatures range from appr ...
(the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
) stretching like taffy. This extension is associated with very low seismic velocities in the upper mantle above approximately depth associated with relatively hot mantle and low degrees of partial melting. This intrusion of the asthenosphere into the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
and
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 ...
is thought to be responsible for nearly all of the volcanism associated with the Rio Grande rift. The sedimentary fill of the basins consists largely of
alluvial fan An alluvial fan is an accumulation of sediments that fans outwards from a concentrated source of sediments, such as a narrow canyon emerging from an escarpment. They are characteristic of mountainous terrain in arid to semiarid climates, but a ...
and
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 incl ...
volcanic flows. The most alkalic lavas erupted outside the rift. The sediments that were deposited during rifting are commonly known as the Santa Fe Group. This group contains
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...
s, conglomerates, and volcanics.
Aeolian deposits Aeolian commonly refers to things related to either of two Greek mythological figures: * Aeolus (son of Hippotes), ruler of the winds * Aeolus (son of Hellen), son of Hellen and eponym of the Aeolians * Aeolians, an ancient Greek tribe thought to ...
are also present in some basins. The Rio Grande rift is intersected in northern New Mexico by the NE-SW trending
Jemez Lineament The Jemez Lineament is a chain of late Cenozoic volcanic fields, long, reaching from the Springerville and White Mountains volcanic fields in East-Central Arizona to the Raton-Clayton volcanic field in Northeastern New Mexico. The lineament ...
which extends well into
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...
. The lineament is defined by aligned volcanic fields and several calderas in the area, including the
Valles Caldera National Preserve Valles Caldera (or Jemez Caldera) is a wide volcanic caldera in the Jemez Mountains of northern New Mexico. Hot springs, streams, fumaroles, natural gas seeps and volcanic domes dot the caldera floor landscape. The highest point in the caldera i ...
in the
Jemez Mountains The Jemez Mountains are a group of mountains in Rio Arriba, Sandoval, and Los Alamos counties, New Mexico, United States. Numerous Puebloan Indian tribes have lived in the Jemez Mountains region since before the Spanish arrived in New Mexico. ...
. The Jemez Lineament is thought to be a hydrous subduction zone scar, separating
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 the ...
basement rock of the
Yavapai The Yavapai are a Native American tribe in Arizona. Historically, the Yavapai – literally “people of the sun” (from ''Enyaava'' “sun” + ''Paay'' “people”) – were divided into four geographical bands who identified as separate, i ...
- Mazatzal transition zone from the Mazaztl Province proper. Also on the Colorado Plateau but further north lies the
San Juan volcanic field The San Juan volcanic field is part of the San Juan Mountains in southwestern Colorado. It consists mainly of volcanic rocks that form the largest remnant of a major composite volcanic field that covered most of the southern Rocky Mountains in t ...
in 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 ...
of Colorado. The youngest eruptions in the rift region are in the Valley of Fires, New Mexico, and are approximately 5,400 years old. The Socorro, New Mexico, region of the central rift hosts an inflating mid-crustal sill-like magma body at a depth of 19 km that is responsible for anomalously high earthquake activity in the vicinity, including the largest rift-associated earthquakes in historic times (two events of approximately magnitude 5.8) in July and November 1906. Earth and space-based geodetic measurements indicate ongoing surface uplift above the Socorro magma body at approximately 2 mm/year. (Doi fails redirect.) File:Riogranderift deepXsection.png, alt=Generalized cross section of the Rio Grande Rift, showing lithospheric and asthenospheric structure., A generalized cross section of the Rio Grande Rift, showing
lithospheric A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the portion of the upper mantle that behaves elastically on time scales of up to thousands of years or ...
and asthenospheric structure. Note the magma lenses and volcanics caused by the welling up of the asthenosphere into the crust, and the thinning of the lithosphere Image:RioGrande Rift RISTRA Seismic Image.jpg, Deep seismic image of the Rio Grande rift compiled from the seismic transect shown in the previous figure, showing inferred mantle flow and imaged crust-mantle ( Moho) topography (after Wilson et al.)(2005).\ File:Riogranderift timeline.png, alt=Timeline for extension and volcanism in the area of the Rio Grande rift., A brief timeline showing extension and volcanism in the Rio Grande rift area. The end of the Laramide orogeny was followed by volcanism and then extension. Changes in lava chemistry are also found, resulting from changes in magmatic sources.


Geologic history

The Rio Grande rift's
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 ...
evolution is fairly complex. The fundamental change in the western margin of the North American plate from one of
subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
to a
transform boundary A transform fault or transform boundary, is a fault along a plate boundary where the motion is predominantly horizontal. It ends abruptly where it connects to another plate boundary, either another transform, a spreading ridge, or a subductio ...
occurred during
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
time. The
Farallon plate The Farallon Plate was an ancient oceanic plate. It formed one of the three main plates of Panthalassa, alongside the Phoenix Plate and Izanagi Plate, which were connected by a triple junction. The Farallon Plate began subducting under the west ...
continued to be subducted beneath western North America for at least 100 million years during Late
Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...
and early
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
time. Compressional and transpressional deformation incurred by 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 o ...
lasted until about 40  Ma in New Mexico. This deformation may have been a result of the coupling between the subducting Farallon plate and the overlying
North American plate The North American Plate is a tectonic plate covering most of North America, Cuba, the Bahamas, extreme northeastern Asia, and parts of Iceland and the Azores. With an area of , it is the Earth's second largest tectonic plate, behind the Pacific ...
. Crustal thickening occurred due to Laramide compression. After the Laramide Orogeny and until 20 Ma, a major period of volcanic activity occurred throughout the southwestern United States. Injection of hot magmas weakened the lithosphere and allowed for later extension of the region.
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
extension Extension, extend or extended may refer to: Mathematics Logic or set theory * Axiom of extensionality * Extensible cardinal * Extension (model theory) * Extension (predicate logic), the set of tuples of values that satisfy the predicate * E ...
started about 30 million years ago (Ma). There are two phases of extension observed: late
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
and middle
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
. The first period of extension produced broad, shallow basins bounded by low-angle faults. The crust may have been extended as much as 50% during this episode. Widespread
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...
tism in mid-
Cenozoic The Cenozoic ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterised by the dominance of mammals, birds and flowering plants, a cooling and drying climate, and the current configura ...
time suggests that the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
was hot, the brittle-ductile transition was relatively shallow. There is evidence that the second period of extension began earlier in the central and northern Rio Grande rift than in the south. A third period of extension may have begun in the early
Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58 One theory is that the Colorado Plateau acts as a semi-independent microplate and one way of explaining the creation of the Rio Grande rift is by the simple rotation of the Colorado Plateau 1-1.5° in a clockwise direction relative to the North American craton. Other explanations that have been offered are that the extension is driven by mantle forces, such as large-scale mantle upwelling or small-scale mantle convection at the edge of the stable craton; collapse of over-thickened continental crust; initiation of transform faulting along the western margin of the North American plate; or detachment of a fragment of the Farallon plate beneath the Rio Grande region that enhanced asthenospheric upwelling in the slab window.


See also

*
Caja del Rio Caja del Rio (Spanish: " box of the river") is a dissected plateau, of volcanic origin, which covers approximately 84,000 acres of land in northern Santa Fe County, New Mexico, United States. The region is also known as the Caja, Caja del Rio Pl ...
*
Geologic timeline of Western North America A timeline of significant geological events in the evolution of Western North America Western North America is the western edge of the North American continent that borders the Pacific Ocean. It consists of Alaska at the farthest north, down t ...
* Lucero volcanic field *
Pajarito Plateau The Pajarito Plateau is a volcanic plateau in north central New Mexico, United States. The plateau, part of the Jemez Mountains, is bounded on the west by the Sierra de los Valles, the range forming the east rim of the Valles Caldera, and on the ea ...
*
Potrillo volcanic field The Potrillo volcanic field is a Monogenetic volcanic field, monogenetic volcanic field located on the Rio Grande Rift in southern New Mexico, United States and northern Chihuahua (state), Chihuahua, Mexico. The volcanic field lies southwest of ...
*
Rio Grande Trail The Rio Grande Trail is a proposed long distance trail along the Rio Grande in the U.S. state of New Mexico. The river extends over 1,800 total miles, some of which pass through the heart of New Mexico. It is the state's primary drainage featur ...


References

{{DEFAULTSORT:Rio Grande Rift Cenozoic rifts and grabens Rio Grande Basin and Range Province Geologic provinces of Colorado Geology of New Mexico Geology of Texas Geology of Mexico