Recent geochronological data show that geon 14 and older rocks are found at least 700 km south of the Grenville front in the eastern Grenville province. In the southwestern Grenville province, comparable rocks extend only 200 km south; farther south, in the Central metasedimentary belt and the Adirondack Mountains, the crust mostly postdates 1350 Ma. We explain this contrast by postulating a major rifting event, commencing at ∼1430 Ma, during which large sections of older crust were detached from that part of southern Laurentia now occupied by the Central metasedimentary belt. Crust was also removed from the area between northwest Britain and Scandinavia. Failed arms extended (1) from Missouri to where the Belt Supergroup accumulated, (2) from the Central metasedimentary belt eastward into Labrador, and (3) between Baltica and east of Greenland. The geologic history following late geon 14 rifting was dominated by a southward-subducting magmatic arc that eventually collided with southern Laurentia-Baltica, resulting in the Elzevirian orogeny at ∼1200 Ma.