The Vadito Group is a

group A group is a number of persons or things that are located, gathered, or classed together. Groups of people * Cultural group, a group whose members share the same cultural identity * Ethnic group, a group whose members share the same ethnic ide ...

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

s that crops out in most of the Precambrian-cored uplifts of northern

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ke ...

Detrital zircon geochronology Detrital zircon geochronology is the science of analyzing the age of zircons deposited within a specific sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead ratio. Zircon is a common accessory or trace ...

and

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 ...

give a consistent age of 1700 Mya for the group, corresponding to the

Statherian The Statherian Period (; grc, σταθερός, statherós, 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 a ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

Description

The Vadito Group is an extensive sequence of

supracrustal rock 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 and volcanic rocks. The oldest minerals on Ear ...

s dominated by feldspathic

gneiss Gneiss ( ) 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. Gneiss forms at higher temperatures a ...

es, feldspathic

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...

s, and

metamorphosed Metamorphic rocks arise from the transformation of existing rock to new types of rock in a process called metamorphism. The original rock (protolith) is subjected to temperatures greater than and, often, elevated pressure of or more, causi ...

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 and conglomerates. Its lower section includes amphibolites, though mafic beds make up less than 10% of the unit. It is found in the

Picuris Mountains The Picuris Mountains are a mountain range in northern New Mexico. They are considered a subrange of the Sangre de Cristo Mountains. Geography The mountains are located to the east of Dixon and surround Picuris Pueblo to the west, north, and ...

, the Tusas Mountains, the Truchas Range, the Mora River area, the Rincon Mountains (), the northern Taos Range, and in the Cimarron Range.

establishes that the principal source regions for the sediments that became the Vadito Group had ages of 1765 to 1704 Mya. The absolute age of the Burned Mountain Formation constituting the upper part of the Vadito Group in the Tusas Mountains is 1700 Mya, based on uranium-lead dating. The Vadito Group is divided into the Big Rock Formation and Burned Mountain Formation in the Tusas Mountains, and the upper Vadito Group is assigned to the

Glenwoody Formation The Glenwoody Formation is a geological formation that is exposed in the cliffs southeast of the Rio Grande Gorge near the town of Pilar and in a few other locations in the Picuris Mountains.Bauer 2004, p. 219 Its minimum age from detrital zirco ...

in the Picuris Mountains. The Burnt Mountain Formation probably correlates with the Glenwoody Formation while the Big Rock Conglomerate corresponds to a

disconformity An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

in the Picuris Mountains. Detrital zircon dating indicates that the Marquenas Formation, formerly assigned to the Vadito Group, has a maximum age of 1435 Mya and is not part of the Vadito Group. The Vadito Group lies structurally above the

Hondo Group The Hondo Group is a group of geologic formations that crops out in most of the Precambrian-cored uplifts of northern New Mexico. Detrital zircon geochronology gives a maximum age for the lower Hondo Group of 1765 to 1704 million years ( Mya), c ...

in the

. However, both groups have been severely deformed and metamorphosed, and the Vadito Group is thought to actually be the older of the two groups.

Cross-bedding In geology, cross-bedding, also known as cross-stratification, is layering within a stratum and at an angle to the main bedding plane. The sedimentary structures which result are roughly horizontal units composed of inclined layers. The origina ...

indicates that the Vadito Group has been overturned. Three metamorphic episodes are recognized in the group. Only the third is well constrained in time, occurring around 1420 Mya and reaching the amphibolite facies. This is likely associated with the

Picuris orogeny The Picuris orogeny was an orogenic event in what is now the Southwestern United States from 1.43 to 1.3 billion years ago in the Calymmian Period of the Mesoproterozoic. The event is named for the Picuris Mountains in northern New Mexico and i ...

. The Vadito Group is interpreted to have been deposited in deep water in a volcanic back-arc basin (the Pilar basin) that opened during the

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 of ...

. File:Vadito Group staurolite.jpg, Staurolite replacing

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

in Vadito Group

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula K Al2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavag ...

bed

Economic geology

The Vadito Group is intruded by the pegmatite of the

Harding Pegmatite Mine The Harding Pegmatite Mine is a former adit mine that extracted lithium, tantalum, and beryllium from a Precambrian pegmatite sill. It ceased operations in 1958 and its owner, Arthur Montgomery, donated it to the University of New Mexico, whi ...

, an historically important source of

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense solid ...

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form m ...

, and

tantalum Tantalum is a chemical element with the symbol Ta and atomic number 73. Previously known as ''tantalium'', it is named after Tantalus, a villain in Greek mythology. Tantalum is a very hard, ductile, lustrous, blue-gray transition metal that ...

. The Vadito Group has also been mined for

kyanite Kyanite is a typically blue aluminosilicate mineral, found in aluminium-rich metamorphic pegmatites and sedimentary rock. It is the high pressure polymorph of andalusite and sillimanite, and the presence of kyanite in metamorphic rocks gener ...

on Mesa La Jara (). Some 1500 tons of kyanite were extracted from Big Rock in 1928, and further prospecting took place in 1948–1949. However, there was no further development of the deposits. The kyanite pods have been interpreted as either metamorphosed

pelitic A pelite (Greek: ''pelos'', "clay") or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock ...

silt Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...

lenses, as unusual pegmatites, or as

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

systems.

History of investigation

The unit was designated as the Vadito

Formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

in 1953 by Arthur Montgomery, who had first taken interest in the geology of the

as a result of his wartime operation of the

. P.E. Long recommended raising it to group rank in 1976 and this was adopted by Bauer and Williams in their sweeping revision of northern New Mexico Precambrian stratigraphy.

Panorama

Footnotes

References

* * * * * * * * * * {{cite journal , last1=Simmons , first1=Mary C. , last2=Karlstrom , first2=Karl E. , last3=Williams , first3=Michael W. , last4=Larson , first4=Toti E. , title=Quartz-kyanite pods in the Tusas Mountains, northern New Mexico: A sheared and metamorphosed fossil hydrothermal system in the Vadito Group metarhyolite , journal=New Mexico Geological Society Field Conference Series , date=2011 , volume=62 , pages=359–378 , url=https://nmgs.nmt.edu/publications/guidebooks/downloads/62/62_p0359_p0378.pdf Geologic groups of New Mexico Precambrian formations of New Mexico Paleoproterozoic geology Proterozoic North America