AGE OF THE WALDEN CREEK GROUP, WESTERN BLUE RIDGE PROVINCE: RESOLVING A DECADES-OLD CONTROVERSY VIA DETRITAL MINERAL GEOCHRONOLOGY AND SEDIMENTARY PROVENANCE ANALYSIS

Previously mapped as upper Precambrian (King et al., 1958), recent discoveries of Paleozoic microfossils (Unrug et al., 2000; Repetski et al. 2006) have placed the Walden Creek Group (WCG), eastern Tennessee, into a younger depositional framework (Silurian or younger). A Paleozoic age requires an origin as an exotic unit emplaced during a later tectonic event or a post-Taconic successor basin. Detrital zircon U-Pb geochronology determined by LA-ICP-MS, feldspar compositions determined by microprobe, and zircon-tourmaline-rutile (ZTR) indices and framework mineral modes determined petrographically, were used to characterize sandstones of the WCG to determine their provenance. Recent provenance analysis of the lower (Snowbird Group: SG) and middle (Great Smoky Group: GSG) Ocoee units (Chakraborty et al. 2012) provides a basis for comparison. Feldspar compositions are sodium poor-Kfs and sodic plagioclase, similar to the SG and GSG. The heavy mineral suite is characterized by being dominated by tourmaline and rutile, rather than zircon, apatite, and epidote, which distinguishes it from SG and GSG, but is similar to the SG and GSG in its low modal abundance of monazite. Detrital zircon U-Pb ages were obtained for three formations of the WCG (seven samples total, n = 620: four samples from the Wilhite Fm., two samples from the Shields Fm., one sample from the Sandsuck Fm.). All grains were imaged by cathodoluminescence to ensure LA analysis of single zircon growth zones. Detrital zircon ages of all units in the WCG show similar distributions. The dominant age modes are at ca. 1000 and 1150 Ma, with smaller modes at 1450 and 650 Ma. The youngest age, 604.7 +/- 5.0, was found in the Wilhite. The two oldest zircon ages of 2695.9 +/-2.6 Ma and 2314.7 +/- 4.1 Ma were found in the Sandsuck sample and are not found in other samples. These patterns closely match the underlying Ocoee Series and their local Mesoproterozoic basement sources. If the WCG units analyzed here are indeed Paleozoic, then it is remarkable that not a single Paleozoic-aged zircon was found. Detrital monazite analysis has been shown to provide higher fidelity provenance ages than zircon, and this method will be carried out on the same samples that were analyzed for detrital zircon geochronology.