CORONATION SILLS OF ARCTIC CANADA: IMPLICATIONS FOR A NEOPROTEROZOIC MANTLE PLUME AND THE BREAK-UP OF RODINIA

The rocks of the 723 Ma Franklin Igneous Event (FIE) of Arctic Canada extend from Greenland in the east to Victoria Island in the west. The Coronation Sills, located on the southern side of the Coronation Gulf of the North American continental margin, are part of the FIE. These mafic sills, typically ~ 70 m thick, are composed of clinopyroxene, plagioclase, olivine and Fe-Ti oxides. They have tholeiitic composition with E-MORB affinities, e_Nd values between +4.2 and +5.9, (La/Yb)_n ~1.5-2, (La/Sm)_n ~1-1.2, and are compositionally similar to other FIE rocks, particularly the Natkusiak flood basalts of Victoria Island. The Coronation Sills have experienced extensive fractionation including flow differentiation during emplacement and show compositional variations with distance from the inferred source region; the dykes/sills distal from the inferred source are more differentiated. It is inferred that these rocks are related to a mantle plume located near Victoria Island at the centre of the radiating dyke swarm. The FIE is an important time marker for the reconfiguration and disintegration of Rodinia, in particular, to determine the location of neighbouring cratons. This event has been related to the rifting and separation between Siberia and northern Laurentia during the break-up of Rodinia. Although the FIE appears to be contemporaneous with current estimates for the breakup of Rodinia, the absence of dykes and sills of similar age and composition in Siberia suggests that Siberia and northern Laurentia were not adjacent to one another at 723 Ma. However, it may favor other proposed locations, e.g. Siberia off either western Laurentia or eastern Baltica. The Franklin Igneous Event could represent an offshoot from the superplume that is related to the breakup of Rodinia.