Sevilleta Metarhyolite
Geologic formation in New Mexico, US
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The Sevilleta Metarhyolite (or Sevilleta Formation) is a geologic formation in central New Mexico. It has a radiometric age of 1665 ± 16 Ma, corresponding to the Statherian period.
| Sevilleta Metarhyolite | |
|---|---|
| Stratigraphic range: | |
Sevilleta Metarhyolite west of Abo Pass, New Mexico, US | |
| Type | Formation |
| Unit of | Manzano Group |
| Underlies | Abajo Formation |
| Overlies | Bootleg Canyon Sequence |
| 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 |
  Sevilleta Metarhyolite (the United States)  Sevilleta Metarhyolite (New Mexico) | |
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. Accessory 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]
The formation is included in the Manzano Group. It overlies the Bootleg Canyon Sequence and is in turn overlain by the Abajo Formation.[5]
Similar beds are found in the Hells 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.[6]