CONSTRAINING PROVENANCE IN THE UINTA/COTTONWOOD ARCH USING LU-HF ISOTOPES

Recent detrital zircon U-Pb age analyses (n=393) of the Little Willow Formation, Utah suggest it to be the lower-most member of the Uinta/Cottonwood Arch (UCA), with major populations identified at >2.5 Ga (Wyoming and/or Superior Craton); 2.0-1.6 Ga, (Mazatzal/Yavapai Terranes); 1.5-1.4 Ga, (Laurentian A-type granites); 1.2-0.9 Ga, (“Grenville-age” orogenic belts); and 0.9-0.7 Ga, (Rodinia-rift magmatism?).

The UCA represents neoproterozoic sediments shed into the failed Uinta-rift beginning approximately ~770 Ma. The detrital signature suggests a varied provenance that became progressively larger as the drainage area expanded with time. The older three populations can be explained as locally derived, whereas the younger two require further explanation.

Several hypotheses have been proposed in explanation of their provenance: 1) a major longitudinal west-flowing river system sourcing detrital grains from eastern Laurentia; 2) a more localized drainage from the south, sourcing grains from the southern arm of the Grenville orogen, or 3) presently buried terranes of similar ages that would have been locally exposed at the time of deposition.

We will report the findings of new U-Pb and Lu-Hf analyses performed on detrital zircons from all three formations: Little Willow Fm., Big Cottonwood Fm., and Uinta Mountain Group. This method will assess the characteristic extent of the formation of juvenile material in the possible source areas, thereby serving as a tool for testing provenance hypotheses.