Sevilleta metarhyolite
The Sevilleta metarhyolite is a geologic suite in central New Mexico. It has a radiometric age of 1665 ± 16 Ma, corresponding to the Statherian period.
| Sevilleta metarhyolite Stratigraphic range: Statherian | |
|---|---|
| Type | Suite |
| Thickness | 4,500 ft (1,400 m) |
| Lithology | |
| Primary | Rhyolite |
| Other | Schist, amphibolite |
| Location | |
| Coordinates | 34.408°N 106.525°W |
| Region | Los Pinos Mountains, New Mexico |
| Country | United States |
| Type section | |
| Named for | Sevilleta land grant, Socorro County, New Mexico |
| Named by | Stark and Dapples |
| Year defined | 1946 |
History of investigation
The unit was first defined by Stark and Dapples in 1959, during their mapping of the Los Pinos Mountains, as the Sevilleta rhyolite.[1] Condie and Budding called the unit the Sevilleta Formation in their 1979 work.[2] Bauer and Pollock called the unit the Sevilleta metarhyolite in their compilation of radiometric ages in 1993.[3]
Geology
The unit is a thick sequence of interbedded metarhyolites, pelitic schists, and amphibolites. The metarhyolite making up the bulk of the unit is a tan to dark red, glassy, fine-grained metarhyolite with abundant potassium feldspar phenocrysts. The modal composition is 25% quartz, 30% plagioclase, 40% potassium feldspar, 1% muscovite, 1% biotite, 1% epidote, 1% oxides, and 1% accessory minerals. Tccessory minerals include actinolite, chlorite, carbonate minerals, and zircon. Radiometric ages range from 1658 Ma to 1670 Ma with a consensus age of 1662±1 Ma.[4]
Similar beds are found in the Hell Canyon area of the northern Manzanita Mountains (34.892°N 106.403°W) and the Monte Largo Hills (35.183°N 106.278°W). However, the Hells Canyon outcrops may be older than the main exposures of the unit. [4]
The unit is interpreted as a product of caldera eruptions associated with the Mazatzal orogeny.[5]
Footnotes
- Stark and Dapples 1959
- Condie and Budding 1979
- Bauer and Pollock 1993
- Grambling et al. 2016, pp.169-170
- Grambling et al. 2016
References
- Bauer, P.W.; Pollock, T.R. (1993). "Compilation of Precambrian isotopicages in New Mexico". New Mexico Bureau of Mines and Mineral Resources Open File Report. 389.
- Condie, K.C.; Budding, A.J. (1979). "Geology and geochemistry of Precambrian rocks, central and south-central New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Memoir. 35. Retrieved 27 May 2020.
- Grambling, Tyler A.; Karlstrom, Karl E.; Holland, Mark E.; Grambling, Nadine L. (2016). "Proterozoic magmatism and regional contact metamorphism in the Sandia-Manzano Mountains, New Mexico, USA" (PDF). New Mexico Geological Society Field Conference Series. 67: 169–175. Retrieved 27 May 2020.
- Stark, J.T.; Dapples, E.C. (1946). "Geology of the Los Pinos Mountains, New Mexico". Geological Society of America Bulletin. 57 (12): 1121–1172.