Palaeomagnetism and the Grenville orogeny: new Rb-Sr ages from dolerites in Canada and Greenland

Rb-Sr mineral data are presented for the Sudbury and Mackenzie dolerites of Canada and for dolerites and lamprophyres from southwest Greenland. Five mineral isochrons or errorchrons, based chiefly upon feldspar separates, agree with twelve biotites from dolerites in defining best-fit ages between 1260 and 1190 m.y. Much older K-Ar and Rb-Sr mineral ages from country rocks demonstrate that the dolerite results are not due to regional heating, and basaltic magmatism in both regions between approximately 1260 and 1190 m.y. is indicated (lambda( 87Rb) = 1.42 X 10-11 yr-1). (Auth.)