Rb-Sr whole-rock and inherited zircon ages of the plutonic suite of the Crossnore Complex, Southern Appalachians, and their implications regarding the time of opening of the Iapetus Ocean

New U-Pb and Rb-Sr isotopic data on the suite of the Crossnore Complex, herein referred to as the Crossnore plutonic suite (CPS), indicate that these plutons crystallized between 680 and 710 m.y. ago; the Crossnore Pluton itself may be as young as approximately 650 m.y. Bulk zircon separates from these rocks contain an older xenocrystic component due to contamination of the CPS magmas by older gneisses. During late Precambrian time, the ancestral Atlantic Ocean basin (Iapetus) formed and separated crustal units which are now part of the Caledonian-Appalachian mountains. These new CPS isotopie data indicate that continental rifting, which preceded the actual formation of the Iapetus Ocean, occurred approximately 690 m.y. ago. The Iapetus Ocean formed 690 to 570 m.y. ago.