The Mazatzal 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 iden ...

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 portions of central

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, US.

Detrital zircon geochronology Detrital zircon geochronology is the science of geochronology, analyzing the age of zircons deposited within a specific sedimentary rock, sedimentary unit by examining their inherent radioisotopes, most commonly the uranium–lead dating, uranium ...

establishes a maximum age for the formation of 1660 to 1630 million years ( Mya), in 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 ...

of the

Precambrian The Precambrian ( ; or pre-Cambrian, sometimes abbreviated pC, 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 t ...

. The group gives its name to the

Mazatzal orogeny The Mazatzal orogeny was an orogenic event in what is now the Southwestern United States from 1650 to 1600 Mya in the Statherian Period of the Paleoproterozoic. Preserved in the rocks of New Mexico and Arizona, it is interpreted as the coll ...

, a mountain-building event that took place between 1695 and 1630 Mya.

Description

The Mazatzal Group consists mostly of fine-grained light-brown to gray

quartzite Quartzite is a hard, non- foliated metamorphic rock that was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tecton ...

which often shows

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 ...

;

metaconglomerate Metaconglomerate is a rock type which originated from conglomerate after undergoing metamorphism. Conglomerate is easily identifiable by the pebbles or larger clasts in a matrix of sand, silt, or clay. Metaconglomerate looks similar to conglome ...

containing

clasts Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks b ...

up to or more in size; and occasional lenses, up to in thickness, of maroon to gray

argillite Argillite () is a fine-grained sedimentary rock composed predominantly of Friability, indurated clay particles. Argillaceous rocks are basically lithified muds and Pelagic sediment, oozes. They contain variable amounts of silt-sized particles. T ...

showing

ripple mark In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water (Ocean current, current or wind wave, waves) or directly by wind. Defining ripple cross-laminae and asymmetric ripples ...

s and

mudcracks Mudcracks (also known as mud cracks, desiccation cracks or cracked mud) are sedimentary structures formed as muddy sediment dries and contracts.Jackson, J.A., 1997, ''Glossary of Geology'' (4th ed.), American Geological Institute, Alexandria, VA ...

. The lower beds of the group are intruded by

rhyolite Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture (geology), texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained matri ...

domes A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...

and sills. The total thickness of the group is up to . The group lies disconformably on top of the Red Rock Rhyolite and is in turn overlain by the Hopi Springs Shale. The group crops out in the Mazatzal Mountains, where it has been strongly deformed (with up to 50% shortening to the northwest) and in the Prescott area, where it has been only mildly

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 ...

. It is also present in the upper Salt River canyon. The group gives its name to the

, a mountain-building event that took place between 1695 and 1630 Mya.

Members

In the northern Mazatzal Mountains, the Mazatzal Group is divided (in ascending stratigraphic order) into the

Deadman Quartzite Deadman or Deadman's may refer to: * "Deadman" or "dead man", are alternative terms for a dead man's switch * "Deadman's foot" is another name for a Salamander in metallurgy * "Deadman anchor" is a buried object (log, concrete, block, etc.) used ...

, the Maverick Shale, and the Mazatzal Peak Quartzite. In the upper Salt River Canyon, the Mazatzal Group is represented by the White Ledges Formation. In the Four Peaks area, the Mazatzal Group is divided (in ascending stratigraphic order) into an informal lower quartzite, an informal lower pelite, and the Four Peaks Quartzite. These are interpreted as a single sequence of sediment deposition. The lower quartzite is an extremely pure quartzite up to thick. The lower pelite is about thick and consists of

pelite A pelite () or metapelite is a metamorphism, 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, i.e. mud or ...

and

psammite Psammite (Greek: ''psammitēs'' "(made) from sand", from ''psammos'' "sand") is a general term for sandstone. It is equivalent to the Latin-derived term areniteU.S. Bureau of Mines Staff (1996) ''Dictionary of Mining, Mineral, & Related Terms.'' ...

beds. The Four Peaks Quartzite is up to thick and is mostly extremely pure quartzite with a few

layers.

History of investigation

The unit was first described by E.D. Wilson in 1922 as the Mazatzal Quartzite. It was raised to group rank in 1981 by P. Anderson and W.R. Wirth. The group was assigned to the Tonto Basin Supergroup in 1988 by Karl Karlstrom and Samuel Bowring.

References

{{Reflist Precambrian Arizona Geologic groups of Arizona Quartzite groups