Discovery of compositionally distinctive rhyolites produced from a peralkaline volcanic center within the late Neoproterozoic Robertson River batholith and which are intercalated with terrestrial deposits of the previously undated Mechum River Formation indicates that rift-related sedimentation and magmatism were ongoing at 702–705 Ma, about 130 m.y. before the breakup of Laurentia. Recognition of late Neoproterozoic age rhyolites in central Virginia indicates that rift-related magmatism was more widespread along the incipient eastern (present coordinates) margin of Laurentia than previously thought. Neoproterozoic rifting in the Blue Ridge province of Virginia appears to have been part of a broad-scale process that affected most, if not all, of the preserved margins of Laurentia. The association of similar, extension-related terrestrial deposits and compositionally distinctive felsic rocks elsewhere may provide a unique marker for testing proposed predrift configurations of the late Neoproterozoic supercontinent, Rodinia.

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