DETRITAL ZIRCON ANALYSIS OF THE NEOPROTEROZOIC TO CAMBRIAN BRIGHAM GROUP IN THE SOUTHERN PORTNEUF RANGE, SOUTHEAST IDAHO

We report new LA ICPMS U-Pb dating at the Arizona LaserChron Lab of detrital zircon populations from the Neoproterozoic (Cryogenian and Ediacaran) to Cambrian Brigham Group in the southern Portneuf Range of SE Idaho. Populations include 1) 2.7-2.6 Ga (Wyoming Province), 2) 1.92-1.66 Ga (Mojave-Yavapai-Mazatzal), 3) 1.5-1.32 Ga (mid-continent granite) and 4) a variable Grenville population of 1.23-1.0 Ga. The data are comparable with previous studies from Brigham Group strata in Utah and equivalent Wood Canyon Fm in California. Early Cambrian strata reveal a significant change from Grenville dominated zircon populations in late Neoproterozoic arkosic and quartz arenites to Yavapai and the mid-continent A-type granite-rhyolite sources for lower Cambrian quartz arenites.

In Utah and southeast Idaho, Neoproterozoic Caddy Canyon, Inkom, Mutual, Camelback Mountain and Browns Hole fms contain all four detrital-zircon populations suggesting mixed Laurentian provenance. Paleocurrents from Mutual Fm in SE Idaho suggest northwestward grain transport with an average azimuth of ~315 degrees. A large change in provenance occurs in lower Cambrian units including Windy Pass Argillite from SE Idaho and correlative Tintic Quartzite from Willard Peak in the Wasatch Range, Utah. The Paleoproterozoic 1.91-1.66 Ga and Mesoproterozoic 1.4 Ga populations are dominant and the Grenville population is negligible.

These data suggest a large late Proterozoic river system delivering sediment derived from the eroding Grenville highlands of eastern and south-central Laurentia. However, the absence of Grenville grains in lower Cambrian marine strata, and the abundance of Yavapai-Mazatzal grains suggests the Sauk transgression prevented delivery of grains to the western miogeocline. Zircon age spectra from the Wood Canyon Fm in California, equivalent to the upper Camelback and Windy Pass fms of the Brigham Group, show a more proximal signature of Grenville-aged (1.11 Ga) zircons that may not be from the Grenville orogenic belt to the east.