Potassium-Argon Dates of Diabase Dyke Systems, District of Mackenzie, N.W.T.

In the Yellowknife geologic province, 2,600-million-year-old granites are cut by three sets of diabase or gabbro dykes: (1) large dykes striking N 70 °E to E-W, (2) rare dykes striking N-S to N 30 °E and (3) an abundant swarm striking N 10 ° - 30 0W. Preliminary potassium-argon dating has been carried out on wholerock samples of the chilled margins and coarse centers of the dykes, and on mineral separates from the dykes and contact aureoles. Data from seventeen dated samples suggest that the dyke sets were intruded during three periods of basaltic magmatism - 2,200, 1,500 and 1000 million years ago. The two earlier periods closely follow the time of emplacement of granites in the Yellowknife and Churchill geologic provinces. The latest diabase dykes occurring in the Yellowknife province are temporally related to a widespread basaltic magmatism, for which the term Keweenawan is most appropriate.
Keywords: analysis, Biotite, biotite, Diabase Dyke Systems, dykes, Potassium-Argon Age, province, Dykes, Granite, Granites, Intrusions, Maps, Rock, Rocks, Sills
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