The Abajo Formation is a

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 ...

in the

Los Pinos Mountains The Los Pinos Mountains are a small mountain range in the central part of New Mexico, US. They are the southernmost part of a mountain front, running north to south, that also includes the Sandia Mountains and the Manzano Mountains. The Los Pinos ...

of 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 was deposited about 1660 million years ( Ma) ago, corresponding to the

Statherian The Statherian Period (; , 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 are defined chronometrically. Th ...

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 ...

History of investigation

The unit was first defined by S.H. Baer in 2004. and assigned to the Manzano Group by Amy Luther in 2006.

Geology

The formation is divided into two members. The Abajo Lithic Arenite consists of various

metasedimentary rock In geology, metasedimentary rock is a type of metamorphic rock. Such a rock was first formed through the deposition and solidification of sediment Sediment is a solid material that is transported to a new location where it is deposited. It occu ...

s interbedded with

amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose ...

s interpreted as metamorphosed

gabbro Gabbro ( ) is a phaneritic (coarse-grained and magnesium- and iron-rich), mafic intrusive igneous rock formed from the slow cooling magma into a holocrystalline mass deep beneath the Earth's surface. Slow-cooling, coarse-grained gabbro is ch ...

ic dikes. The Abajo Schist consists of metasedimentary

schist Schist ( ) is a medium-grained metamorphic rock generally derived from fine-grained sedimentary rock, like shale. It shows pronounced ''schistosity'' (named for the rock). This means that the rock is composed of mineral grains easily seen with a l ...

interbedded with metamorphosed

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic dikes and flows. The formation is interpreted as sediments deposed during a period of volcanic activity. Detrital zircon grains in the formation are almost identical in age and isotope composition to the underlying Sevilleta metarhyolite, suggesting that the sediments of the quartzite were weathered almost exclusively from local sources. The minimum zircon age is about 1660 Ma, and

radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to Chronological dating, date materials such as Rock (geology), rocks or carbon, in which trace radioactive impurity, impurities were selectively incorporat ...

of underlying and overlying formations place the age of the formation at about this time.

References

{{Reflist Precambrian formations of New Mexico Paleoproterozoic magmatism Proterozoic North America Schist formations