A MODEL FOR THE APPALACHIAN ORIGIN OF PALEOZOIC TERRANES IN THE NORTH AMERICAN CORDILLERA

A belt of terranes of uncertain affinity runs the length of the North American Cordillera outboard of the Paleozoic passive margin and inboard of clearly exotic Mesozoic arc and accretionary wedge terranes (Wrangellia, Cache Creek, Franciscan, and Guerrero terranes). It includes the Yukon Tanana (YT) terrane in Alaska and Yukon; the Dorsey (DY), Kootenay (KO), and Barkerville (BV) terranes, and the Rapid River tectonite (RRT) of the Slide Mountain terrane in Canada; the Yreka (YR), Eastern Klamath (EK), and Northern Sierran (NS) terranes in the western US; and the Acatlan complex (AC) of the Mixteca terrane in Mexico. We propose that these terranes originated in the Appalachian realm, where they remained through the Acadian orogeny. Critical geologic characteristics that are inconsistent with a Cordilleran origin but correlate directly with the Acadian and pre-Acadian history of the Appalachians unify the terranes: either (1) intensely tectonized metamorphic host rocks and Devono-Mississipian arc granitoids (similar to the core of the Acadian orogen but unlike coeval Antler tectonics of the Cordillera) (YT, DY, RTT, YR, EK, NS, and AC); or (2) late Precambrian to mid Paleozoic sedimentary sequences that are not homologous with those of the Cordilleran passive margin because (a) Cambrian platformal strata are followed by deep water lithologies indicating profound subsidence (consistent with Taconic loading of the Iapetan margin but not with the Cordillera’s thermal subsidence history) (KO and BV), or (b) early Paleozoic sandstones lie outboard of the coeval Cordilleran shale-out (YR and NS). Following the Acadian orogeny, these terranes were detached and displaced south by rift and/or transform plate boundary motion that reestablished the Appalachian continental margin prior to the Alleghenian collision. Once subduction resumed in Iapetus, these terranes were swept west along the southern rim of North America and into the paleo-Pacific, where they would be transported north by closure of the Caborca-Golconda-Slide Mountain-Angayucham ocean.