Petrogenesis of the 723 Ma Coronation sills, Amundsen basin, Arctic Canada: Implications for the break-up of Rodinia

The Coronation mafic sills and associated Natkusiak flood basalts in Arctic Canada are part of the ∼723Ma Franklin igneous events, a flood basalt and dyke swarm province that extends across the southern Arctic of North America and Greenland. Two representative sills, 70 and 25m thick, respectively outcrop near Coronation Gulf in Nunavut. They are composed of clinopyroxene, plagioclase, olivine and Fe-Ti oxides, and have tholeiitic composition similar to the Natkusiak basalts. Their ε_Nd values range between +4.2 and +5.9 and have (La/Yb)_n ratios of ∼1.5-2. These rocks are mantle derived and were affected by minor crustal contamination. Compositional variations indicate that the Coronation sills have experienced extensive fractionation including flow differentiation during emplacement and show increased differentiation from, west to east, across the province, a feature similar to the Mackenzie dyke swarm. However, the Mackenzie dyke swarm and the Franklin igneous events have distinct chemical composition. The Franklin rocks are related to a mantle plume located near Victoria Island at the center of the dyke swarm and could represent an offshoot from the superplume related to the break-up of Rodinia. The absence of such dykes and sills in Siberia argues against locating Siberia against northern Laurentia in a Rodinia reconstruction.