Some Reflections on the Mesoproterozoic Belt Purcell Basin

Some Reflections on the Mesoproterozoic Belt. Purcell Basin David Mogk, Montana State University Paul Mueller, University of Florida Carol Frost, University of Wyoming

Current Tectonostratigraphic Configuration of the Belt Supergroup from Sears et al. , 2007

Lydon (2007) Geology and metallogeny of the Belt-Purcell Basin

From Vuke et al. , 2009

Pre-Belt Basement Sample Localities and Primary Ages does not include xenocrysts ages Clearwater & related (1. 86 & 2. 6 Ga) Pioneer gneiss (1. 86 Ga) Great Falls tectonic zone Little Belt gneisses (1. 79 -1. 86 Ga), Medicine Hat (2. 6 -2. 7 Ga) Montana Metasedimentary Terrane (3. 2 -3. 4 Ga with 2. 45 & 1. 77 Ga overprint) Biltmore gneiss (1. 89 Ga) Beartooth Mountains (2. 75 -2. 85 Ga) Medicine Lodge Creek (2. 45 Ga) Bloody Dick Creek (1. 9 Ga) Armstead gneiss (2. 73 Ga)

Neihart Quartzite: Little Belt Mountains Rests unconformably on GFTZ basement KDE plot f GFTZ Youngest zircon is 1. 71 Ga 207 Pb/206 Pb Age (Ma)

La. Hood Formation Conglomerate Matrix, Jefferson Canyon f 207 Pb/206 Pb Age (Ma)

La. Hood Formation Siltstone from Golden Sunlight Mine Mode shifts from 3. 5 -3. 6 Ga to 3. 2 -3. 4 Ga 2. 7 and 1. 8 Ga appear f Youngest zircon measured in the La. Hood is 1. 78 Ga Armstead/Gravelly 207 Pb/206 Pb Age (Ma)

La. Hood Siltstone Horseshoe Hills Spanish Peaks f Mode continues at 3. 2 -3. 4, BBMZ appears GFTZ zircons persist 3. 5 -3. 6 Ga persists, but diminished Great Falls/Big Sky Beartooth Bighorn 207 Pb/206 Pb Age (Ma) Note: Only 3 grains > 10% discordant 3. 58 Ga

Western conjugate of the Belt Basin? Siberia? SWEAT or No SWEAT?

Questions About the Belt Basin • What is the provenance of the sediments? • What is the tectonic and depositional environments of deposition? • Are the lower Belt units actually Pre-Belt? • What is the western conjugate of the Belt Basin? Siberia? SWEAT? • What is basement to the Belt basin, and how did this influence the geometry of the Basin? Control of younger Sevier-style structures? • How did the Belt Basin accommodate 20 km of deposition? • What controls metallogenesis in the Belt Basin: