PROVENANCE OF CENTRAL AND WESTERN BLUE RIDGE PARAGNEISSES, SOUTHWESTERN NORTH CAROLINA

Recent detrital zircon geochronologic studies have vastly increased our knowledge of provenance of southern Appalachian terranes (e.g. Bream et al., 2004). It has also generated new questions regarding the affinities and relationships between different terranes. Dominance of 1.1–1.25 Ga detrital zircons in combinations with other Early and Middle Proterozoic ages imply a post-Grenville, Laurentian provenance for most southern Appalachian terranes. Central Blue Ridge (cBR) terranes in southwestern NC and northeastern GA, including the Dahlonega gold belt (DGB) and Cowrock terranes contain Late Archean grains distinguishing them from other Blue Ridge terranes and implying a possible Gondwanan connection prior to the Taconic. Three additional samples from cBR (Cartoogechaye terrane [Ct] and DGB), and one from the western Blue Ridge (wBR) were collected for ion microprobe geochronology of detrital zircons to further understand the provenance of these terranes. Ct samples include metasandstone from Chunky Gal Mountain (CGM) near Franklin, NC, and migmatitic biotite gneiss (W18) from near Waynesville, NC. The single DGB metasandstone (HAZ) was collected from within the Great Balsam Mountains window, the northernmost extent of the DGB, near Balsam, NC. These samples contain abundant 1.0, 1.1, and 1.2 Ga detrital zircons with lesser components of 1.3, 1.4, and 0.7–0.9 Ga, possibly constraining maximum age of deposition. No Archean grains were observed in these samples, and the oldest detrital zircon observed was 1.8 Ga from W18. Metamorphic rims from CGM (~463 Ma) and HAZ (~455) are consistent with other studies documenting a Taconic, 460-450 Ma tectonothermal event affecting the cBR. The Ordovician (?) Mineral Bluff Formation (MBF) occurs in core of the Murphy syncline and may be the youngest unit in the wBR. Metasandstones and phyllites of the MBF yielded detrital zircons of 1.0, 1.1, 1.3, and 1.4 Ga, with single grain analyses of 1.6, 1.7, 1.8, 1.9, 2.1 and 2.7 Ga, similar to published detrital zircons from the DGB. No Paleozoic zircons were observed in the MBF and the maximum age of deposition is constrained by a 0.77 Ga grain. Although a mixed Gondwanan affinity is possible for the MBF, dominance of 1.0–1.2 Ga with lesser 1.3 and 1.4 Ga zircons support a post-Grenville, Laurentian provenance of cBR and wBR terranes.