Precise zircon geochronology in the Adirondack Lowlands and implications for revising plate-tectonic models of the Central Metasedimentary Belt and Adirondack Mountains, Grenville province, Ontario and New York

New high-precision, single-grain dating of leucogranites from the Adirondac k Lowlands, dated previously by multigrain zircon methods at ca. 1416 Ma (W ellesley Island) and ca. 1285-1230 Ma (Hyde School Gneiss), has yielded U-P b zircon ages of ca. 1172 Ma, identical to that of Rockport granite of the Frontenac terrane. In addition, sensitive high resolution ion microprobe (S HRIMP) zircon dating of the intrusive Antwerp-Rossie suite in the Adirondac k Lowlands indicates a maximum emplacement age of ca. 1207(-11)(+26) Ma whi ch fixes a minimum age for deposition of regional metasedimentary rocks tha t it crosscuts. These results remove apparent chronological discrepancies a cross the St. Lawrence River, thus expanding the significance of the Rockpo rt granite and Hyde School Gneiss and requiring modification of plate-tecto nic models for the Central Metasedimentary Belt and Adirondack Mountains in the interval ca. 1350-1125 Ma.