At https://phys.org/print431943147.html … geologists disprove theory about what stopped the formation of the Mid Continent Rift (in N America). This rift is generally thought responsible for the dramatic cliffs running along the shore of Lake Superior (where ice melt has scoured away sedimentary layers that once covered it …
… it seems the rift is much longer than previously thought. South of Lake Superior the volcanic rocks of the rift are covered by younger rocks. It seems the rift was found as far south as Oklahoma. Rift valleys have the ability, given enough time and enough seismology, to split continents.