Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Missouri Buttes

stripes

Occurrence number: 
174-00-069
Country: 
United States
Region: 
Wyoming
Location: 
Longitude: -104.77, Latitude: 44.62
Carbonatite: 
No

A ring of four prominent phonolite plugs rising 150-250 m together with a ridge, also of phonolite, are separated by talus slopes but probably coalesce at depth. The phonolite is highly porphyritic with phenocrysts of alkali feldspar, nepheline and aegirine-augite/aegirine in a groundmass of the same minerals, apatite and magnetite.

Age: 
K-Ar on aegirine from phonolite gave 49.6 ± 1.7 Ma (McDowell, 1971, p. 15) and fission-track dating of sphene from the northwestern plug gave 55.5 ± 7.1 Ma (Hill et al., 1975).
References: 

DARTON, N.H. and O'HARRA, C.C. 1907. Devils Tower Folio: Wyoming. Geologic Atlas of the United States: 150.
HILL, D.J., IZETT, G.A. and NAESER, C.W. 1975. Early Tertiary fission track ages of sphene from Devils Tower and Missouri Buttes, Black Hills, northeastern Wyoming. Abstracts with Programs, Geological Society of America, 7: 613-4.
MCDOWELL, F.W. 1971. K-Ar ages of igneous rocks from the western United States. Isochron/West, New Mexico Bureau of Mines and Mineral Resources, 2: 1-16

Location: 
All locations > North America > United States > Wyoming
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith