- Usage in publication:
-
- Keokirk Quartz Diorite*
- Modifications:
-
- Named
- Dominant lithology:
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- Quartz diorite
- AAPG geologic province:
-
- Montana folded belt
Summary:
Named for exposures on Keokirk Mountain in the Vipond Park quad, Beaverhead Co, MT in Montana folded belt province. These exposures are the type locality. Composed of fine-grained, dark-gray, uniform-textured quartz diorite. Is one of five plutonic units of Pioneer batholith. Has biotite K-Ar age of 72.6 +/-2.5 m.y.; hornblende K-Ar ages of 79.8 +/-2.2 and 80.3 +/-2.3 m.y.; sphene F-T of 76.5 +/-7.5 m.y. Is assigned to the Late Cretaceous. Cut by Grayling Lake Granite (new) and by Trapper Tonalite (new).
Source: GNU records (USGS DDS-6; Denver GNULEX).
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).