The Franklin intrusions are an extensive swarm of late Hadrynian (latest Proterozoic) diabase dikes that are present in an arc from Great Bear Lake eastward to Melville Peninsula, Baffin Island, and northern Ungava Bay. They are chemically and petrologically classified as tholeiites and are probably comagmatic. Paleomagnetic pole positions and numerous whole-rock K-Ar age determinations indicate that the dikes were emplaced at low latitudes 650 m.y. ago. They intrude Hadrynian sedimentary sequences that contain features indicative of depositon under warm climatic conditions.

The Baffin dikes are subparallel with the northeast coastline of Baffin Island and with a pronounced northwest-trending fault system. Intermittent, mainly normal movement along these faults persisted from the Helikian to the Quaternary and produced a series of graben structures which may be due to the same regional tension as the dikes. Thus, Baffin Bay and Davis Strait may have begun to form as early as the late Hadrynian, and they may contain Paleozoic strata.