| The North American Intermountain West preserves the Belt Supergroup, one of the best records
of Mesoproterozoic strata on Earth; however, debate remains about first-order interpretations of
basin formation in the region. We investigated a package of Mesoproterozoic strata at Leaton
Gulch near Challis, Idaho. Results suggest the Leaton Gulch stratigraphic section was deposited
in a fluvial setting <1400–1300 Ma, spanning the poorly documented interval between
traditionally interpreted cessation of the Belt Supergroup and recently characterized Deer Trail
Group. Leaton Gulch strata demonstrate similar sediment provenance to the upper Belt
Supergroup but are ~70 Ma younger. Porcellanites found within Leaton Gulch and surrounding
upper-Belt strata show radiogenic εHf(t), interpreted as a mix of primary mantle and remelted
metasedimentary sources. Zircon trace element data of the porcellanite from Leaton Gulch
suggests a high-silica melt source. Collectively, we interpret that the strata of Leaton Gulch
record late-stage rifting of the Nuna Supercontinent.
Key words: Belt Supergroup, Nuna, supercontinent, detrital zircon, porcellanite |