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

摘要: Rb-Sr mineral data are presented for the Sudbury and Mackenzie dolerites of Canada lamprophyres from southwest Greenland. Five isochrons or errorchrons, based chiefly upon feldspar separates, agree with twelve biotites in defining best-fit ages between 1260 1190 m.y. Much older K-Ar country rocks demonstrate that dolerite results not due to regional heating, basaltic magmatism both regions ∼1260 is indicated (λ(87Rb) = 1.42 × 10−11 yr−1). This activity can be correlated extensive sills Sweden Finland, subject parallel studies, which yield six ten biotite dolerites, determinations by other methods falling 1290 1155 m.y., although all grouped 1250-1210 range. Palaeomagnetic poles define tight clusters each Canada/Greenland Fennoscandia. Superimposition two groups leads a non-unique reconstruction Fennoscandia may have adjoined at 1260-1190 but an orientation quite different established 1000-850 The necessary net rotation through 90° been achieved splitting, separation final reunion continents into relative disposition ∼1190 ∼1000 This favours involvement plate tectonic processes Grenville-Sveconorwegian orogeny. represent beginning continental preceded Grenville orogeny, causes cannot ruled out.