Reference 1504
M'Gonigle, John W; Dalrymple, G Brent (1996) U. S. Geological Survey Bulletin, Report: B 2132, 17 pp., 1 sheet,1996
| Authors | M'Gonigle, John W; Dalrymple, G Brent |
|---|---|
| Year | 1996 |
| Source | U. S. Geological Survey Bulletin, Report: B 2132, 17 pp., 1 sheet,1996 |
| ISSN | 8755-531X |
| GeoRef | 1996-047285 |
| Keywords | absolute age; alkali feldspar; Ar/Ar; ash-flow tuff; basins;Beaverhead County Montana; biotite; Cenozoic; Challis Volcanics;correlation; dates; depositional environment; emplacement; Eocene;feldspar group; fluvial environment; framework silicates; geologicmaps; igneous rocks; lacustrine environment; maps; mica group;Montana; North America; Paleogene; paludal environment; plagioclase;pyroclastics; rhyolites; Rocky Mountains; sanidine; sedimentarybasins; sedimentation; sheet silicates; silicates; single-crystalmethod; southwestern Montana; Tertiary; tuff; U. S. Rocky Mountains;United States; USGS; volcanic rocks |
Abstract
super 40 Ar/ super 39 Ar ages of single sanidine, biotite, andplagioclase crystals were obtained from eighteen samples of rhyoliticintrusives, tuffs, and ash-flow tuffs from southwestern Montana. Thesevolcanic rocks are part of a thick volcanic sequence in severaltopographic basins and in adjacent highlands. The analyses show thatthe volcanic rocks were emplaced between about 48.76+ or -0.17 Ma and45.04+ or -13 Ma and are temporally correlative with the EoceneChallis Volcanic Group of central Idaho.
19 samples from this reference
| Sample | Rock name | Major | Trace | Isotope |
|---|---|---|---|---|
| 91-169 | Rhyolite | |||
| 91-168 | Rhyolite | |||
| 82-528 | Tuff | |||
| 82-504 | Rhyolite | |||
| Tcq | Rhyolite | |||
| 87-64 | Pyroclastic-fall | |||
| 88-100 | Pyroclastic-fall | |||
| Tcl | Tuff | |||
| 91-171 | Pyroclastic-fall | |||
| 89-135-3 | Pyroclastic-fall | |||
| 88-59 | Rhyolite | |||
| 81-189 | Rhyolite | |||
| 82-322 | Rhyolite | |||
| 82-551 sanidine 1 | Pyroclastic-fall | |||
| 82-551 sanidine 2 | Pyroclastic-fall | |||
| 89-135-4 | Pyroclastic-fall | |||
| 87-63 | Rhyolite | |||
| 91-170 | Pyroclastic-fall | |||
| 91-104 | Pyroclastic-fall |