Lamprophyre dikes and the Leading Tickles dunite from Notre Dame Bay. Nfld., were sampled for a paleomagnetic study to define their age relationships and the tectonic implications of their emplacements. A single normal polarity direction (328°, +62°) was obtained by alternating field and thermal treatment, from 10 Cretaceous lamprophyre dikes. The paleopole (2I2°E, 67°N) derived from these dikes agrees with the cluster of North American Cretaceous paleopoles. On the other hand. I he Leading Tickles dunite recorded two magnetizations: one (206°, +32°) related to the time of intrusion and interpreted to be Ordovician; the second one (000°, +66°). an overprint, is related to the intrusion of the lamprophyre dikes and interpreted to be Cretaceous. The polarity, paleopole, radiometric age, and tectonic setting of the lamprophyre dikes when compared with the Isachsen dikes. N.W.T., suggest the opening of the North Atlantic Ocean was initiated in the Lower Cretaceous.

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