Foliated granite plutons in the Long Range give a Rb–Sr whole rock age of 1130 ± 90 m.y. and a K–Ar biotite age of 840 ± 20 m.y. These ages agree with other Grenville dates and may be fitted into the Grenville pattern. The K–Ar age of 805 ± 35 m.y. for the diabase dike swarm is also taken as the age of the Lighthouse Cove Formation on Belle Isle. This demonstrates that there is probably a non-sequence between this formation and the overlying Lower Cambrian sediments. The low initial 87Sr/86Sr ratio of 0.702 ± 0.004 indicates that these dikes have a deep crustal or mantle origin.

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