Ortega Formation | |
---|---|
Stratigraphic range: | |
Type | Formation |
Unit of | Hondo Group |
Underlies | Rinconada Formation |
Overlies | Vadito Group |
Thickness | 8,000 m (26,000 ft) |
Lithology | |
Primary | Quartzite |
Other | Metaconglomerate |
Location | |
Coordinates | 36°26′28″N106°04′26″W / 36.441°N 106.074°W |
Region | Tusas and Picuris Mountains, New Mexico |
Country | United States |
Type section | |
Named for | Ortega Mountains |
Named by | Just |
Year defined | 1937 |
Ortega Formation outcrops in New Mexico |
The Ortega Formation is a geologic formation that crops out in most of the mountain ranges of northern New Mexico. Detrital zircon geochronology establishes a maximum age for the formation of 1690-1670 million years (Mya), in the Statherian period of the Precambrian. [1]
The Ortega Formation consists of a very clean (98% modal quartz [2] ), typically bluish-white, quartzite, with some beds near the base of the formation composed of metaconglomerate. [3] Crossbedding is found throughout the formation, and aluminosilicate minerals are abundant within the formation. These show that its lower beds were buried deeply enough to be metamorphosed to the sillimanite facies, at temperatures of over 500 °C (930 °F). [2] The Ortega Formation is the principal ridge-forming formation of the Picuris Mountains and is a uniform 800–1,200 meters (3,000–4,000 ft) thick. [2]
The contact between the Ortega Formation and the underlying Vadito Group is fairly easy to trace using a regional manganese-rich marker bed in the uppermost Vadito Group. [4] This is a ductile shear zone associated either with mountain collapse at the end of the Mazatzal orogeny or tectonics of the Picuris orogeny that resulted in south-directed displacement of the Ortega Formation over the Glenwoody Formation. Structurally, the Ortega Formation tends to form stiff limbs within which weaker formations are heavily distorted. The Ortega Formation is quite uniform in thickness everywhere but the northern Picuris Mountains, where its thickness appears to have been doubled by tectonic imbrication. [5]
The Ortega Formation may correlate with the Uncompahgre Formation of Colorado, the Mazatzal Group in Arizona, and other Proterozoic quartzite successions associated with the Yavapai and Mazatzal orogenies. [6] These all appear to be first cycle sandstones, in which the individual sand grains have eroded out of igneous or metamorphic rock rather than been recycled from older sedimentary rock. Their remarkable maturity (they were formed from nearly pure quartz grains) may be a result of deep weathering processes acting on the original sediment beds under unusual Proterozoic conditions. [7]
The formation is interpreted as the first stage of a marine transgression on a southward-dipping siliciclastic shelf. This was likely part of a back-arc basin associated with the Yavapai orogeny, named the Pilar basin. [1] [6] Tabular cross-bedding permits the orientation of the highly distorted beds to be determined. [8]
The unit was named by Evan Just in 1937 during his investigation of pegmatites in northern New Mexico. Just included the entire sequence of quartzite and quartz schist in the Picuris Mountains in his definition, assigning the schist to the Rinconada schist member, [3] and including the feldspathic Petaca Schist in the Tusas Mountains. [9] Arthur Montgomery recognized the Rinconada schist as well but included the Pilar slate in the Ortega Formation [10] while assigning some of the schist and conglomerate beds to his Vadito Formation. [11] During mapping of the Las Tablas area, Barker redefined the Ortega Quartzite to include only the quartzite and basal conglomerate beds. [8] In their sweeping revision of the Precambrian stratigraphy of Northern New Mexico, Bauer and Williams split the Glenwoody Formation from the Ortega Formation and defined the Ortega Formation to consist only of the massive quartzite and basal conglomerate beds [4] while reassigning the Petaca Schist mostly to the Vadito Group (Burned Mountain Formation). [12]
The Manzano Group is a group of geologic formations in central New Mexico. These have radiometric ages of 1601 to 1662 million years (Ma), corresponding to the late Statherian period of the Paleoproterozoic.
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 collision of the 1700-1600 Mya age Mazatzal island arc terrane with the proto-North American continent. This was the second in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
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 New Mexico and Arizona, it is interpreted as the collision of the 1800-1700 Mya age Yavapai island arc terrane with the proto-North American continent. This was the first in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
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 interpreted either as the suturing of the Granite-Rhyolite crustal province to the southern margin of the proto-North American continent Laurentia or as the final suturing of the Mazatzal crustal province onto Laurentia. According to the former hypothesis, this was the second in a series of orogenies within a long-lived convergent boundary along southern Laurentia that ended with the ca. 1200–1000 Mya Grenville orogeny during the final assembly of the supercontinent Rodinia, which ended an 800-million-year episode of convergent boundary tectonism.
The Moppin Complex is a Precambrian geologic complex found in the Tusas Mountains of northern New Mexico. It has not been directly dated, but is thought to be Statherian based on a minimum age of 1.755 Gya from radiometric dating of magmatic intrusions.
The Vadito Group is a group of geologic formations that crops out in most of the Precambrian-cored uplifts of northern New Mexico. Detrital zircon geochronology and radiometric dating give a consistent age of 1700 Mya for the group, corresponding to the Statherian period.
The Big Rock Formation is a formation that crops out in the Tusas Mountains of northern New Mexico. Detrital zircon geochronology gives a maximum age for the formation of 1665 Mya, corresponding to the Statherian period.
The Burned Mountain Formation is a geologic formation that crops out in the Tusas Mountains of northern New Mexico. It has a U-Pb radiometric age of 1700 Mya, corresponding to the Statherian period.
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. Its minimum age from detrital zircon geochronology is 1.693 Mya, corresponding to the Statherian period.
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), corresponding to the Statherian period.
The Rinconada Formation is a geologic formation that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology establishes a maximum age for the Rinconada Formation of about 1723 Mya, placing it in the Statherian period of the Precambrian.
The Pilar Formation is a geologic formation that crops out in the Picuris Mountains of northern New Mexico. It has a radiometric age of 1488 ± 6 million years, corresponding to the Calymmian period.
The Piedra Lumbre Formation is a geologic formation that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology yields a maximum age of 1475 million years, corresponding to the Calymmian period.
The Marquenas Formation is a geological formation that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology gives it a maximum age of 1435 million years, corresponding to the Calymmian period.
The Joaquin quartz monzonite is a Mesoproterozoic pluton in northern New Mexico. Radiometric dating gives it an age of 1460 million years, corresponding to the Calymmian period.
The Uncompahgre Formation is a geologic formation in Colorado. Its radiometric age is between 1707 and 1704 Ma, corresponding to the Statherian period.
The Trampas Group is a group of geologic formations that crops out in the Picuris Mountains of northern New Mexico. Detrital zircon geochronology yields a maximum age of 1475 million years, corresponding to the Calymmian period.
The White Ridge Quartzite is a geologic formation in central New Mexico. It has a maximum age of 1650 million years (Ma), corresponding to the Statherian period.
The Abajo Formation is a geologic formation in the Los Pinos Mountains of central New Mexico. It was deposited about 1660 million years (Ma) ago, corresponding to the Statherian period.
The Mazatzal Group is a group of geologic formations that crops out in portions of central Arizona, US. Detrital zircon geochronology establishes a maximum age for the formation of 1660 to 1630 million years (Mya), in the Statherian period of the Precambrian. The group gives its name to the Mazatzal orogeny, a mountain-building event that took place between 1695 and 1630 Mya.