Monturaqui is an

impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact crater ...

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

. It lies south of the

Salar de Atacama Salar de Atacama is the largest salt flat in Chile. It is located south of San Pedro de Atacama, is surrounded by mountains, and has no drainage outlets. In the east it is enclosed by the main chain of the Andes, while to the west lies a secondar ...

and was formed 663,000 ± 90,000 years ago by the impact of an

IAB meteorite IAB meteorites are a group of iron meteorites according to their overall composition and a group of primitive achondrites because of silicate inclusions that show a strong affinity to winonaites and chondrites. Description The IAB meteorites are ...

. It is wide and deep and contains a salt pan. Only a few remnants of the meteorite that formed the crater have been collected, with most of the rocks being of local origin. The crater was discovered in 1962 and identified as an impact crater in 1966.

Human history

The crater was first suspected to be an impact crater in 1962, when it was found on aerial images. After geologic research on the site found evidence of the impact event, it was identified as an impact crater in 1966. The crater has not been drilled. Its name is derived from the mountain range where it is located and from the town of Monturaqui . The closest town is

Peine Peine (; Eastphalian: ''Paane'') is a town in Lower Saxony, Germany, capital of the district Peine. It is situated on the river Fuhse and the Mittellandkanal, approximately west of Braunschweig, and east of Hanover. History A deed from 11 ...

, northeast of the crater. An old Inka road, which goes from the Pacific Ocean to

San Pedro de Atacama San Pedro de Atacama is a Chilean town and commune in El Loa Province, Antofagasta Region. It is located east of Antofagasta, some 106 km (60 mi) southeast of Calama and the Chuquicamata copper mine, overlooking the Licancabur volcano. ...

and further to Argentina, runs from the crater. The crater has been deemed by Stanislav Kaniansky and Kristian Molnár to be one of the "most impressive" in the world and has a high scenic and historical value. The Chilean Geological Society has defined it as one of the

geosite Geoheritage is the geological aspect of natural and cultural heritage. A geosite is a particular geoheritage asset. The word is a blend of ''geological'' and ''heritage''. It is thus a heritage category comparable to other forms of natural he ...

s of Chile, although such a classification has no legal effect and the crater is threatened by erosion caused by vehicles and the over-collection of rocks. In 2017, several Chilean organizations and the community of Peine petitioned the Chilean government to declare the site a

historic monument A monument is a type of structure that was explicitly created to commemorate a person or event, or which has become relevant to a social group as a part of their remembrance of historic times or cultural heritage, due to its artistic, his ...

. Monturaqui crater is a

tourist Tourism is travel for pleasure or business; also the theory and practice of touring (disambiguation), touring, the business of attracting, accommodating, and entertaining tourists, and the business of operating tour (disambiguation), tours. Th ...

attraction in the area.

Geography and geomorphology

Monturaqui lies in a remote region of the

Atacama Desert The Atacama Desert ( es, Desierto de Atacama) is a desert plateau in South America covering a 1,600 km (990 mi) strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert is the driest nonpolar desert in th ...

south of the

, in the " precordillera". The city of

Antofagasta Antofagasta () is a port city in northern Chile, about north of Santiago. It is the capital of Antofagasta Province and Antofagasta Region. According to the 2015 census, the city has a population of 402,669. After the Spanish American wars ...

lies northwest of the crater. Administratively, the crater is in the

Antofagasta Region The Antofagasta Region ( es, Región de Antofagasta, ) is one of Chile's sixteen first-order administrative divisions. The second-largest region of Chile in area, it comprises three provinces, Antofagasta, El Loa and Tocopilla. It is bordered t ...

. Monturaqui is a nearly circular, well-preserved wide and deep

. It has the shape of a bowl and is elongated in northwest-southeast direction. The height of its rim ranges between with the southern rim being about higher than the northern. Sedimentation in rain-fed ponds has left a playa in the crater, which lies in its northeastern quadrant and is surrounded by lake sediments. Bushes grow close to the salt pan deposits and it could be considered a "salt pan oasis". The dry climate (the annual precipitation is less than ) means that water in the crater tends to evaporate. A

magnetic anomaly In geophysics, a magnetic anomaly is a local variation in the Earth's magnetic field resulting from variations in the chemistry or magnetism of the rocks. Mapping of variation over an area is valuable in detecting structures obscured by overlying ...

is associated with the crater. It is located at about elevation. The terrain in the area consists of

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

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 under ...

s that are covered by

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...

s, and slopes northward to the Salar de Atacama, thus explaining the tilt of the crater. Dykes cut through the granitic units, and both ignimbrites and granites are faulted. The impact primarily affected the granitic units but both units are apparent in the crater walls and the ignimbrites cover the rim crest.

Impact event

The impact has been dated with

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares ...

to have occurred about 663,000 ± 28,000 years ago. Various

surface exposure dating Surface exposure dating is a collection of geochronological techniques for estimating the length of time that a rock has been exposed at or near Earth's surface. Surface exposure dating is used to date glacial advances and retreats, erosion histo ...

techniques yield ages of about 500,000–780,000 years. Since then, erosion has altered the crater by depositing fluvial and

mass wasting Mass wasting, also known as mass movement, is a general term for the movement of rock or soil down slopes under the force of gravity. It differs from other processes of erosion in that the debris transported by mass wasting is not entrained in ...

deposits in it, gullying its sides and by lowering the rim. Originally, the Monturaqui crater was connected with the

Campo del Cielo Campo del Cielo refers to a group of iron meteorites and the area in Argentina where they were found. The site straddles the provinces of Chaco and Santiago del Estero, located north-northwest of Buenos Aires, Argentina and approximately south ...

or the Rio Cuarto impact structures in Argentina. The meteorite probably hit from the northwest at an angle of 41° and was travelling at a velocity of about . Because of the elevation at which it hit the ground, the meteorite had traversed only a little more than half the atmosphere and thus had not lost as much mass as it would have had it hit ground at sea level. The impact heated the ground to temperatures exceeding , probably reaching , and had an energy comparable to that of 2.2 Hiroshima bombs. The formation of the crater disrupted the local

drainage Drainage is the natural or artificial removal of a surface's water and sub-surface water from an area with excess of water. The internal drainage of most agricultural soils is good enough to prevent severe waterlogging (anaerobic condition ...

network, which redeveloped to run around the crater.

Impactor

The impacting body was a metallic asteroid containing

iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

. It has been identified as a group I

octahedrite Octahedrites are the most common structural class of iron meteorites. The structures occur because the meteoric iron has a certain nickel concentration that leads to the exsolution of kamacite out of taenite while cooling. Structure Octahedr ...

and as an

with a size of about .

Impact products

The impact has produced rocks such as

impact glass Impactite is rock created or modified by one or more impacts of a meteorite. Impactites are considered metamorphic rock, because their source materials were modified by the heat and pressure of the impact. On Earth, impactites consist primarily o ...

coesite Coesite is a form ( polymorph) of silicon dioxide Si O2 that is formed when very high pressure (2–3 gigapascals), and moderately high temperature (), are applied to quartz. Coesite was first synthesized by Loring Coes Jr., a chemist at the ...

and

shocked quartz Shocked quartz is a form of quartz that has a microscopic structure that is different from normal quartz. Under intense pressure (but limited temperature), the crystalline structure of quartz is deformed along planes inside the crystal. These pl ...

; some rocks were completely melted during the impact and others were turned to

glass Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...

. Impact-generated rocks formed mostly from granite and meteorite material. They are mostly found at the east-southeast side of the crater, with lesser amounts on its inside. Only a few or no fragments of the meteorite have been recovered. Given the proximity of the crater to an old road, this may be due to traders and herdsmen removing meteorite fragments but it may also be due to the metals being oxidized over time. They include rocks called "iron shale", they are magnetic indicating their origin in the meteorite. The nonoxidized parts consist of

cohenite Cohenite is a naturally occurring iron carbide mineral with the chemical structure ( Fe, Ni, Co)3 C. This forms a hard, shiny, silver mineral which was named by E. Weinschenk in 1889 after the German mineralogist Emil Cohen, who first described ...

, rabdite,

schreibersite Schreibersite is generally a rare iron nickel phosphide mineral, , though common in iron-nickel meteorites. It has been found on Disko Island in Greenland and Illinois. Another name used for the mineral is rhabdite. It forms tetragonal crystals ...

and

taenite Taenite is a mineral found naturally on Earth mostly in iron meteorites. It is an alloy of iron and nickel, with a chemical formula of and nickel proportions of 20% up to 65%. The name is derived from the Greek ταινία for "band, ribbon" ...

. Other minerals are

goethite Goethite (, ) is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient t ...

lepidocrocite Lepidocrocite (γ-FeO(OH)), also called esmeraldite or hydrohematite, is an iron oxide-hydroxide mineral. Lepidocrocite has an orthorhombic crystal structure, a hardness of 5, specific gravity of 4, a submetallic luster and a yellow-brown stre ...

maghemite Maghemite (Fe2O3, γ-Fe2O3) is a member of the family of iron oxides. It has the same spinel ferrite structure as magnetite and is also ferrimagnetic. It is sometimes spelled as "maghaemite". ''Maghemite'' can be considered as an Fe(II)-deficie ...

pentlandite Pentlandite is an iron–nickel sulfide with the chemical formula . Pentlandite has a narrow variation range in Ni:Fe but it is usually described as having a Ni:Fe of 1:1. It also contains minor cobalt, usually at low levels as a fraction of wei ...

and reevesite. Metallic

spherule A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ...

s occur. Fragments of the Monturaqui meteorite have been collected in the meteorite collection of "

Giorgio Abetti Prof Giorgio Abetti H FRSE (5 October 1882 – 24 August 1982) was an Italian solar astronomer.G. GodolABETTI, Giorgio Dizionario Biografico degli Italiani (in Italian) Life He was born in Padua, the son of noted astronomer Antonio Abetti. He ...

" Astronomical Observatory and Museum, San Giovanni in Persiceto,

Bologna Bologna (, , ; egl, label=Emilian language, Emilian, Bulåggna ; lat, Bononia) is the capital and largest city of the Emilia-Romagna region in Northern Italy. It is the seventh most populous city in Italy with about 400,000 inhabitants and 1 ...

, Italy. File:Monturaqui meteorite, Chile - University of Arizona Mineral Museum - University of Arizona - Tucson, AZ - DSC08499.jpg File:Impactites from Monturaqui Impact Crater.jpg

References

Citations

General sources

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External links

* * {{Impact cratering on Earth Atacama Desert Impact craters of Chile Landforms of Antofagasta Region Pleistocene Chile Pleistocene impact craters