U-Pb ages of metarhyolites of the Catoctin and Mount Rogers formations, central and southern Appalachians: evidence for two pulses of Iapetan rifting

Abstract

U-Pb ages of zircon from rhyolites of the Catoctin and Mount Rogers Formations demonstrate that rifting of the Laurentian continent to form the Iapetus Ocean was a prolonged event spanning 200 m.y. involving two important pulses of extrusive igneous activity. Rhyolitic flows of the non-fossiliferous Catoctin and Mount Rogers Formations, long correlated with one another on the basis of similar stratigraphic constraints, are dated at 564 ± 9 Ma and 758 ± 12 Ma, respectively. The data suggest a history of rifting in the central and southern Appalachians spanning 200 m.y. near the end of the Late Proterozoic. The earliest pulses did not proceed to continental separation and are not recorded north of the Potomac River. The later pulse or pulses affected the area from Newfoundland (ages of 617-590 Ma) to North Carolina and resulted in the opening of the Iapetus Ocean. -from Authors