SEARCHING FOR GRENVILLIAN LINKAGES BETWEEN LAURENTIA AND AMAZONIA: GOING DOWN THE RABBIT HOLE AND FINDING “THAT PESKY WABBIT” IN THE GREAT SMOKY MOUNTAINS BASEMENT COMPLEX OF SOUTHEASTERN LAURENTIA AND PARAGUA BLOCK IN SOUTHWESTERN AMAZONIA

A paleogeographic link between SE Laurentia and SW Amazonia of broadly Grenvillian age (1.2-1.0 Ga) during Rodinian assembly has been recognized for decades. Numerous studies searched for potential linkages, with the Sunsas belt of SW Amazonia commonly proposed based on a general correspondence of magmatic and metamorphic ages. However, Pb isotopes demonstrated a clear distinction between Laurentian and Amazonian crust, leading to the “exotic Amazonia” hypothesis for the origin of Grenvillian south-central Appalachian basement (SCAB) being transferred from Amazonia. Although high quality paleomagnetic data support a spatial linkage at 1.2 to 1.1 Ga. numerous complexities for the linkage remain. New zircon U-Pb ages and Pb isotope compositions for Grenville basement of the southernmost French Broad Massif (FBM) in the eastern Great Smoky Mountains Basement Complex (GSMBC) support the following: (1) the GSMBC is a correlative of the Mars Hill terrane based on Pb isotopes, the presence of Geon 1.3-1.9 detrital zircons, abundant 1.05 to 0.95 Ga (Ottawan-Rigolet) metamorphic zircon, and pre-Ottawan/Rigolet depositional ages for oldest metasediments; (2) pre-Elzevirian 1.37-1.32 Ga magmatic rocks (orthogneisses) and mafic xenoliths in the GSMBC correlate with similar-aged rocks in the Adirondacks, Ontario and northern Appalachian basement massifs that were the pre-Grenvillian outboard margin of Laurentia behind which Elzevirian (1.25 to 1.20 Ga) basins and magmatism developed; (3) Pb isotopes of pre-Elzevirian GSMBC granitic gneisses and mafic xenoliths/enclaves indicate mixing of Amazonian and Laurentian crustal components during generation of pre-Elzevirian GSMBC magmas; (4) the Paragua Block of SW Amazonia consists of the ~1.34-1.32 Ga San Ignacio granite suite (SIGS) that intrudes paragneisses of the Paleoproterozoic San Ignacio Group; (5) the GSMBC and SIGS orthogneisses contain inherited 1.7-1.8 Ga zircon. We propose the GSMBC, FBM and by extension the SCAB is a rifted fragment of the Paragua block behind which Elzevirian-age magmatism and sedimentation occurred. Collision with Laurentia occurred in pre-Elzevirian time closing a pre-Grenville ocean basin. Amazonia and Laurentia then collided during the Shawinigan orogeny at which time the Paraqua block was re-accreted to SW Amazonia.