SUPERCONTINENT BREAKUP, DIACHRONOUS RIFTING, AND DISPERSAL OF MICROCONTINENTS: THE LAURENTIAN MARGIN OF IAPETUS
Post-rift transition along the Laurentian Blue Ridge margin (New York promontory to Alabama promontory) at ~543 Ma constrains the time of breakup, as well as the minimum age of rifting of microcontinents, now re-accreted Appalachian internal basement massifs (e.g., Pine Mountain, Sauratown Mountains, Baltimore domes). The age of a sandstone-carbonate (now quartzite-marble) passive-margin cover on the microcontinents is unconstrained and might represent either ~750 or ~565 Ma rifting and breakup. In contrast, the passive-margin cover of the Argentine Precordillera indicates rifting from the Ouachita embayment of Laurentia during Early Cambrian time (~530 Ma), followed by dispersal and accretion to western Gondwana. Early to Middle Cambrian graben-filling sediment of the Mississippi Valley-Rough Creek-Rome fault system of eastern Laurentia is coeval with rifting of the Precordillera from the Ouachita embayment, and the fault system outlines a potential microcontinent that failed to separate from Laurentia.