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

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

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

5. From Vuke et al., 2009

6. Pre-Belt Basement Sample Localities and Primary Ages
does not include xenocrysts ages
Clearwater & related
(1.86 & 2.6 Ga)
Great Falls tectonic zone
Little Belt gneisses ( Ga),
Medicine Hat ( Ga)
Montana Metasedimentary Terrane
( Ga with 2.45 & 1.77 Ga overprint)
Pioneer gneiss
(1.86 Ga)
Biltmore gneiss
(1.89 Ga)
Beartooth Mountains
( Ga)
Armstead gneiss
(2.73 Ga)
Medicine Lodge Creek
(2.45 Ga)
Bloody Dick Creek
(1.9 Ga)

7. Neihart Quartzite: Little Belt Mountains
Rests unconformably on GFTZ basement
KDE plot f
GFTZ
Youngest zircon is 1.71 Ga
207Pb/206Pb Age (Ma)

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

9. LaHood Formation 207Pb/206Pb Age (Ma)
Siltstone from Golden Sunlight Mine
Mode shifts from Ga
to Ga
2.7 and 1.8 Ga appear f
Youngest zircon measured
in the LaHood is 1.78 Ga
Armstead/Gravelly
207Pb/206Pb Age (Ma)

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

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

12. 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: