PALEOZOIC TECTONICS OF THE NORTH AMERICAN CORDILLERA: A CARIBBEAN MODEL

Early to late Paleozoic geodynamic models of the North American Cordillera assume roughly continental margin parallel convergence. For example, early Paleozoic paleogeographic models depict an arc approaching the continental margin until accretion in the Late Devonian/Early Mississippian. Similar geodynamic scenarios exist for middle to Late Paleozoic. Sonomia in the western U.S. Cordillera and the peri-cratonic terranes of Canada and Alaska. We regard this view of the North American Cordillera as highly problematic.. While some arc systems appear to have been constructed on oceanic basement (Antler/Sonoma arcs) others were built upon continental crust (peri-cratonic terranes). Moreover, the only significant exposure of early Paleozoic arc rocks in the Cordillera is the Alexander terrane which has long been regarded as exotic to western Laurentia. Two other early Paleozoic convergent margin terranes (N. Sierran-E. Klamath) are volumetrically minor. The Alexander and E. Klamath terranes have Neoproterozoic basement evocative of a peri-Gondwanan setting. In the case of the Alexander terrane, the Neoproterozoic basement was heavily intruded by Ordovician-Silurian plutons and mantled by the coeval Descon formation. This phase of arc activity was interrupted by the Late Silurian/Early Devonian Klakas Orogeny which ended with deposition of early Devonian Karheen red beds. The eastern Klamath terrane records a similar history. Devonian sandstones from both possess a distinctive non western Laurentian 1.5-1.6 Ga detrital zircon component as does the Sierra City Melange in the N. Sierra. Recognized sources for significant quantities of this age zircon include Australia, the Baltic Shield, and the Amazon craton. Faunal data support a location near Baltica for the Alexander terrane in the Late Silurian. Terranes either attributed to the Antler arc or the basement of mid to late Paleozoic arcs may contain fragments of the Alexander terrane based on our new detrital zircon data. Determining how these terranes were delivered to their current positions along the western margin of Laurentia will give insight to plate configurations during the early to late Paleozoic. Following Wright and Wyld (2006) we consider a Caribbean/Scotia style arc system.