The Sandia granite is a

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 ...

in central

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 ...

. It has a radiometric age of 1453±12 Ma, corresponding to the

Calymmian The Calymmian Period (from , meaning "cover") is the first geologic period in the Mesoproterozoic Era and lasted from Mya to Mya (million years ago). Instead of being based on stratigraphy, these dates are defined chronometrically. The peri ...

period Period may refer to: Common uses * Period (punctuation) * Era, a length or span of time *Menstruation, commonly referred to as a "period" Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (o ...

Description

The Sandia granite is prominently exposed along the east flank of 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 ...

, with almost of exposure at

Sandia Crest Sandia Crest, also known locally as Sandia Peak or simply as the Crest, is a mountain ridge that, at , is the highpoint of the Sandia–Manzano Mountains, and is located in the Sandia Mountains of Bernalillo County, New Mexico, United State ...

. It extends from Placitas to

Tijeras Canyon Tijeras Canyon (sometimes also referred to as Tijeras Pass) is a prominent canyon in the central part of the U.S. state of New Mexico. It separates the Sandia Mountains subrange to the north from the Manzano Mountains subrange (specifically the l ...

. Its radiometric age is 1453±12 Ma. The pluton is a single body with significant heterogeneities. The primary phase is

monzogranite Monzogranite is a plutonic rock that occupies the middle of the QAPF diagram, consisting of between 20–60% quartz, and of the remainder, between 35–65% alkali feldspar and the remainder plagioclase. Examples Pilgangoora belt, Pilbara c ...

with a secondary phase of

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 ...

. It is notable for the presence of local outcrops of

orbicular granite Orbicular granite (also known as orbicular rock or orbiculite) is an uncommon plutonic rock type which is usually granitic in composition. These rocks have a unique appearance due to ''orbicules'' - concentrically layered, spheroidal structures, p ...

. Both major phases contain

diorite Diorite ( ) is an intrusive rock, intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is Intermediate composition, inter ...

inclusions that are interpreted as co-mingled melts. Exposures are typically gray to pink, medium-to-coarse grained, monzogranite.

Aplite Aplite () is an intrusive igneous rock that has a granitic composition. Aplites are fine-grained to aphanitic Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not vi ...

and

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic c ...

dikes crosscut by

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The Atom, atoms are linked in a continuous framework of SiO4 silicon–oxygen Tetrahedral molecular geometry, tetrahedra, with each oxygen being shared between two tet ...

veins are common. The average modal composition is 28% quartz, 25% potassium

feldspar Feldspar ( ; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagiocl ...

, 38%

plagioclase Plagioclase ( ) is a series of Silicate minerals#Tectosilicates, tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continu ...

, 8%

biotite Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron- endmember annite, and the magnesium-endmember phlogopite; more al ...

, and 1% accessory minerals, including

magnetite Magnetite is a mineral and one of the main iron ores, with the chemical formula . It is one of the iron oxide, oxides of iron, and is ferrimagnetism, ferrimagnetic; it is attracted to a magnet and can be magnetization, magnetized to become a ...

titanite Titanite, or sphene (), is a calcium titanium nesosilicate mineral, Ca Ti Si O5. Trace impurities of iron and aluminium are typically present. Also commonly present are rare earth metals including cerium and yttrium; calcium may be partly rep ...

zircon Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of th ...

hornblende Hornblende is a complex silicate minerals#Inosilicates, inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common ...

apatite Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of Hydroxide, OH−, Fluoride, F− and Chloride, Cl− ion, respectively, in the crystal. The formula of the admixture of ...

, and

muscovite Muscovite (also known as common mica, isinglass, or potash mica) is a hydrated phyllosilicate mineral of aluminium and potassium with formula KAl2(Al Si3 O10)( F,O H)2, or ( KF)2( Al2O3)3( SiO2)6( H2O). It has a highly perfect basal cleavage y ...

. There are three generations of deformation preserved in the

contact aureole Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...

that indicate regional deformation. Microstructure and foliation in the aureole indicate east-west compression and north-south extension during and shortly after pluton emplacement, but the pluton interior is undeformed. Pluton emplacement involving heating to ~650°C at pressures of 2-3 kbars, corresponding to a depth of 7-10 km. The pluton is interpreted as having been emplaced syntectonically at middle crustal depth during 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 ...

. Though there is no local extrusive equivalent, the western Granite-Rhyolite provinces east of the Rocky Mountains may be an extrusive equivalent.

History of investigation

The unit was first defined by Kelley and Northrop in 1975. The name has continued in common use in spite of being preempted by the Sandia Formation.

Footnotes

References

* * * {{cite journal , last1=Kelley , first1=V.C. , last2=Northrop , first2=S.A. , year=1975 , title=Geology of the Sandia Mountains and vicinity, New Mexico , journal=New Mexico Bureau of Mines and Mineral Resources Memoir , volume=29 , url=https://geoinfo.nmt.edu/publications/monographs/memoirs/downloads/29/Memoir-29.pdf , accessdate=21 September 2020 Precambrian formations of New Mexico Paleoproterozoic magmatism Proterozoic North America