Rubio Peak Formation

Rubio Peak Formation
Stratigraphic range: Eocene PreꞒ Ꞓ O S D C P T J K Pg N
Monument Peak, located near Lake Valley, New Mexico, USA, is underlain by Rubio Peak Formation.
Type	Formation
Unit of	Spears Group
Underlies	Sugarlump Tuff
Overlies	early Tertiary plutons
Thickness	5,000 feet (1,500 m)
Location
Coordinates	32°41′24″N107°53′40″W / 32.6899504°N 107.8944869°W / 32.6899504; -107.8944869
Region	New Mexico
Country	United States
Type section
Named by	W.E. Elston
Year defined	1953
Rubio Peak Formation (the United States) Show map of the United States Rubio Peak Formation (New Mexico) Show map of New Mexico

The Rubio Peak Formation is a geologic formation located in southwestern New Mexico. ^[1] It is thought to have been deposited in the Eocene Epoch. ^[2]

Description

The formation is volcanic, consisting mostly of flows of amphibole latites to pyroxene andesites ^[2] and associated volcaniclastics and tuffs. ^[3] The flows have a silica content of 59-63%. The appearance is highly variable, from pinkish gray to red to brown to black, with large to small phenocrysts and with glassy to fully crystalline texture. However, the chemical composition is reasonably uniform across the formation. ^[2] The maximum thickness is as much as 5,000 feet (1,500 m). It lies on older Tertiary intrusive rocks and is overlain ^[3] and interfingers with ^[4] the Sugarlump Tuff.

Oxygen isotope ratios suggest that the magma from which the formation solidified had its origin in the Earth's mantle and underwent a degree of fractional crystallization. ^[5]

The formation has not been directly dated. However, the overlying Sugarlump Tuff has been radiometrically dated as 35.17±0.12 million years old, so the Rubio Peak Formation cannot be younger than this nor older than the Tertiary rocks on which it was deposited. This suggests an Eocene age for the formation. ^[6]

Fossils

The formation contains Duchesnean and early Chadronian mammal fossils. These included a jaw of the brontothere Duchesneodus. ^[7]

History of investigation

The formation first appears informally in a chart prepared by R.M. Hernon and coinvestigators in 1953, ^[1] but was apparently first used in an unpublished paper by W.E. Elston that same year. ^[8] C.H. Dane and G.O. Bachman (1961) mapped the formation throughout southwestern New Mexico and extended the definition to include some flows that appeared to be of Cretaceous age, ^[9] but subsequent work has restricted the definition to flows near the type area and of Eocene to Olicocene age. ^[4] The formation was assigned to the Spears Group by Steven M. Cather and coinvestigators in 1994, who excluded the volcanic units and restricted the formation to the associated volcaniclastics. ^[10]

Footnotes

1. Hernon, Jones & Moore 1953.
2. Clemons 1982.
3. Hernon, Jones & Moore 1964.
4. Strangway, Simpson & York 1976.
5. Hoffman & Michelfelder 2018.
6. Kelley 2021.
7. Lucas 2015, p. 154.
8. Jicha 1954.
9. Dane & Bachman 1961.
10. Cather, Chamberlin & Ratte 1994.

References

• Cather, Steven M.; Chamberlin, R.M.; Ratte, J.C. (1994). "Tertiary stratigraphy and nomenclature for western New Mexico and eastern Arizona" (PDF). New Mexico Geological Society Field Conference Series. 45: 259–266. Retrieved 25 August 2020.
• Clemons, R.E. (1982). "Geology of Massacre Peak quadrangle, Luna County, New Mexico". New Mexico Bureau of Mines and Mineral Resources Geologic Map. 51. Retrieved 6 August 2020.
• Dane, C.H.; Bachman, G.O. (1961). "Preliminary geologic map of the southwestern part of New Mexico". U.S. Geological Survey Miscellaneous Investigations Series Map. I-344. Retrieved 6 August 2020.
• Hernon, R.M.; Jones, W.R.; Moore, S.L. (1953). "Some geological features of the Santa Rita quadrangle" (PDF). New Mexico Geological Society Field Conference Guidebook. 4: 117–129. Retrieved 6 August 2020.
• Hernon, R.M.; Jones, W.R.; Moore, S.L. (1964). "Geology of the Santa Rita quadrangle, New Mexico". U.S. Geological Survey Geologic Quadrangle Map. GQ-306. Retrieved 6 August 2020.
• Hoffman, M.; Michelfelder, G.S. (2018). "Oxygen isotope variations in Paleogene volcanic rocks from southern New Mexico: Insight on crustal contamination and magmatic sources" (PDF). New Mexico Geological Society Field Conference Series. 69: 189–196. Retrieved 11 March 2021.
• Jicha, H.L. Jr. (1954). "Geology and mineral deposits of Lake Valley quadrangle, Grant, Luna, and Sierra Counties, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Bulletin. 37. Retrieved 6 August 2020.
• Kelley, Shari A. "Cookes Peak". New Mexico Bureau of Geology & Mineral Resources. New Mexico Tech. Retrieved 15 July 2021.
• Lucas, Spencer G. (2015). Lucas, S.G.; Sullivan, R.M. (eds.). "Fossil Vertebrates in New Mexico". New Mexico Museum of Natural History and Science Bulletin. Eocene fossil vertebrates of New Mexico. 68: 149–157. Retrieved 15 July 2021.
• Strangway, D.W.; Simpson, J.; York, D. (1976). "Paleomagnetic studies of volcanic rocks from the Mogollon Plateau area of Arizona and New Mexico". New Mexico Geological Society Special Publication. 5: 119–125.