U-PB AND HF-ISOTOPIC ANALYSIS OF ZIRCONS FROM THE NEOPROTEROZOIC (CRYOGENIAN) FORMATION OF PERRY CANYON, NORTHERN UTAH

The Neoproterozoic formation of Perry Canyon in the Wasatch Range of northern Utah contains two diamictites separated by an intervening sandstone and argillite member and records Early Cryogenian glaciations and Rodinian rifting. We report four LA-ICPMS detrital-zircon age spectra and two SHRIMP U-Pb Concordia ages that show a distinct change in maximum depositional age as well as provenance between the diamictites.

The lower diamictite contains a significant, youngest detrital zircon grouping at 708 ± 5 Ma (SHRIMP), which allows correlation with the “Sturt I” glacial event identified in Namibia, South China and the Yukon Territory of North America. The overlying sandstone has a distinctly younger grouping at 671 ± 5 Ma (SHRIMP) suggesting the sandstone and the upper section of the formation of Perry Canyon in the northern Wasatch Range is correlative with the upper diamictite of the Scout Mountain Member at Portneuf Narrows of southeastern Idaho. Thus a 40 m.y. break may separate deposition of the lower and upper glacial Perry Canyon units pointing towards diachronous Sturtian glacial events.

Along with distinctive young populations there is also a change in provenance between the lower diamictite and sandstone. Three lower diamictite samples contain major peaks at ~2500 Ma likely coming from the nearby southern Wyoming province. The middle sandstone instead contains a dominant Paleoproterozoic (~1700 Ma) population that is weak or absent in all other samples. Epsilon Hf analyses on the ~1700 Ma zircons show that they all contain a positive, juvenile signatures making Paleoproterozoic accreted terranes, located to the south and west, the likely sources.

In the youngest (~670-710 Ma) zircons from the diamictite and sandstone initial εHf values range from -22 to -2, indicating that they were derived from an evolved source. Calculated model crustal residence ages range from 2.7–1.5 Ga, suggesting melting from Archean and Proterozoic crust.

A thick, well exposed section of the formation of Perry Canyon on Fremont Island in the Great Salt Lake also contains both glacial intervals. A lower dropstone-bearing member, upper diamictite and upper mafic volcanic member have been sampled for detrital zircons and geochemistry.