U-PB ZIRCON AND GEOCHEMICAL DATA REVEAL PALEOPROTEROZOIC ORTHOGNEISS AND AN EAST KOOTENAY OROGENY MESOPROTEROZOIC DIKE AT TUBBS HILL, COEUR D’ALENE, IDAHO, SOUTHEAST PRIEST RIVER COMPLEX

Sensitive High Resolution Ion Microprobe (SHRIMP) U-Pb zircon data and geochemical data revise the age of the orthogneiss comprising the majority of Tubbs Hill in Coeur d’Alene, Idaho from Cretaceous to Paleoproterozoic. Orthogneiss zircons yielded U-Pb core and rim spot dates clustered around 2.4 Ga, 1.8 Ga, 1.5 Ga, 1.25 Ga and rims around 49.8 Ma; clusters have 5 spots dates on average. Priest River Complex rock units exposed SSW of Tubbs Hill are made up of antiformal Neoarchean (2.6 Ga) amphibolite and Paleoproterozoic (1.86 Ga) orthogneiss that trend along a NNE axial trace directly towards Tubbs Hill. Trace element data from the Tubbs Hill orthogneiss are strikingly similar to Loft’s Bay orthogneiss (1.86 Ga), which crops out 8 miles south. Zircon rim dates clustered around 49.8 Ma likely formed during exhumation along with Eocene dikes present both locally and regionally. A pegmatitic, felsic, meter-scale dike of Tubbs Hill yielded a U-Pb zircon date of 1367 ± 3.4 Ma. The regional East Kootenay Orogeny (1379 to 1325 Ma) is a middle Proterozoic deformational and metamorphic event with evidence found in Belt-Purcell Basin rocks of east-central Idaho as well as southern British Columbia. This dike date marks the first direct evidence for the East Kootenay Orogeny within the Priest River Complex. All major regional geologic events are now known to be represented in the Priest River Complex demonstrating that the complex is valuable tectonic piercing point.