THE SOUTHERN APPALACHIAN TERRANE MOSAIC: AN UNRESOLVED CUSTODY BATTLE

The Phanerozoic history of terrane accretion along the eastern margin of Laurentia remains incompletely constrained. Following Neoproterozoic breakup of Rodinia and the formation of the Iapetus Ocean, Ordovician to Permian amalgamation of Pangea trapped suspect and exotic terranes in the crystalline core of the Appalachian orogen. Mesozoic rifting of Pangea stranded some of the these terranes on the eastern margin of Laurentia, yet their boundaries and compositions remain uncertain. Thus, the history of terrane accretion remains a challenge to Laurentian tectonic reconstructions. Here we present U-Pb detrital-zircon ages collected from metasedimentary rocks of Carolinia, the Piedmont Zone, and the eastern Blue Ridge of the southern Appalachians to further our understanding of the provenance and age constraints of these terranes. Following disaggregation and separation, detrital zircons were mounted and analyzed using laser-ablation single-collector inductively coupled plasma mass-spectrometry at the University of South Carolina’s Center for Elemental Mass Spectrometry. Resulting age distributions reveal provenance characteristics not previously known for these regions. A sample from Carolinia is dominated by ca. 420-450 Ma zircons and contains a subordinate Cambro-Ordovician population; together this age distribution differs significantly from dominantly Neoproterozoic age distributions known from elsewhere in Carolinia. A sample from the Cat Square terrane yields age populations that broadly overlap with Proterozoic and early Paleozoic ages known from other Cat Square terrane samples, but is dominated by a wide late Neoproterozoic population that is absent from those samples. A sample from the Eastern Tugaloo terrane is composed of Paleozoic zircons with peaks at ca. 340 Ma, 380 Ma and 450 Ma. A sample from the Western Tugaloo terrane yielded zircon ages that resemble the known Grenville ages for this terrane, while also producing a significant Devonian-Mississippian population generally not recognized in Blue Ridge metasedimentary rocks. Together, these data suggest that additional age mapping of southern Appalachian terranes should further elucidate their boundaries, compositions and provenance.