THE AGES OF CARBONATITE COMPLEXES IN EASTERN CANADA

Abstract

There are four chronological groups of carbonatite complexes in Ontario and Quebec. These are about 125 m.y., 565 m.y., 1075 m.y., and 1700 m.y., with a possible fifth at 1560 m.y. The recently proposed St. Lawrence Rift System is not considered to be a very likely control of carbonatite emplacement unless it includes a widespread system of branch faults. The coincidence of carbonatite complexes with the "Kapuskasing High" is striking and probably puts a minimum age of 1750 m.y, on the feature. Niobium is found in carbonatites of each age group.