EXAMINING THE IAPETUS "RIBBON CONTINENT" RIFT MODEL: RIFT-DRIFT HISTORY OF THE RED SEA AND ATLANTIC MARGINS

Stratigraphic and isotopic data strongly suggest separation of the Laurentian Iapetus margin from other parts of the Rodinian supercontinent in two stages. Bimodal volcanic sequences in the southern-central Appalachian Mt. Rogers Formation point to an earlier, 760-700 Ma failed rifting event, whereas 572 – 564 Ma flood basalts of the Catoctin Formation suggest that successful rifting leading to Iapetan seafloor spreading occurred in the latest Neoproterozic. Younger rifting events, including separation of the Argentine Precordillera and Dashwoods block from the Laurentian margin, suggest that even younger rifting events may have separated Laurentian microcontinental blocks into an already open Iapetus Ocean during the earliest Paleozoic. Chilhowee equivalent drift facies rocks of the Appalachians have been traditionally interpreted as representing the transition to passive margin sedimentation on the Laurentian Iapetus margin. However, based on paleomagnetic reconstructions and a protracted history of rift volcanism, some workers have proposed that a "ribbon continent" was separated from Laurentia during the Cambrian, following the opening of Iapetus, resulting in the formation of a narrow seaway along the length of the Laurentian margin. In this ribbon continent model, drift strata deposited on the Neoproterozoic-earliest Paleozoic Laurentian shelf record the history of this younger event, and not development of the Iapetan passive margin. The rift-drift history of the Red Sea and North American Atlantic rifted margins may provide excellent insights into these contrasting views. Because their rift-drift history has not been obscured by convergent margin tectonics, their stratigraphic and volcanic records provide excellent detail on the development of evolving ocean basins. As such, their rift-drift histories suggest that rifting of Laurentian microcontinental blocks into Iapetus may have been isolated occurrences, and not necessarily a margin wide event suggested in the ribbon continent model.