Reference 732
Toth, Margo I; Stacey, John S (1992) U. S. Geological Survey Bulletin, Report: B 2008, 14 pp., 1992
| Authors | Toth, Margo I; Stacey, John S |
|---|---|
| Year | 1992 |
| Source | U. S. Geological Survey Bulletin, Report: B 2008, 14 pp., 1992 |
| ISSN | 8755-531X |
| GeoRef | 1992-009874 |
| Keywords | absolute age; batholiths; Bitterroot Lobe; Bitterroot Range; Cenozoic;continental crust; Cretaceous; crust; dates; diorites; emplacement;feldspar group; framework silicates; genesis; geochronology; granites;granodiorites; Idaho; Idaho Batholith; Idaho County Idaho; igneousrocks; intrusions; isotopes; lead; lower crust; magmas; Mesozoic;metals; monazite; Montana; monzogranite; nesosilicates; North America;northern Idaho; orthosilicates; Paleoproterozoic; phosphates; plutonicrocks; plutons; Precambrian; Proterozoic; protoliths; Ravalli CountyMontana; Rocky Mountains; silicates; Tertiary; tonalite; U. S. RockyMountains; U/Pb; United States; upper Precambrian; USGS; westernMontana; zircon |
Abstract
Zircons from tonalite emplaced along the western periphery of theBitterroot Lobe of the Idaho Batholith yield an almost concordant ageof 94+ or -1.4 Ma; monzogranite and granodiorite plutons along thenorthern edge of the lobe yield ages of 75 to 71 Ma. Thevolumetrically more dominant plutons in the central and western partsof the lobe were emplaced between 59 and 54 Ma. Upper intercept data,combined with Pb isotopic data from feldspars, confirm that the magmasof the Bitterroot Lobe were derived mainly from an early Proterozoiclower continental crust.