Palaeomagnetic and potassium-argon dating studies of the Tasmanian dolerites

The stable magnetizations of the Tasmanian Dolerites are shown to fall into two distinct groups depending upon their directions and the geographical region of the dolerites. It has been suggested that this could be a result of significant age differences between the dolerites of these groups. A series of K-Ar determinations indicates that there is no detectable systematic age differences and the average of the five bodies dated is 170.5 ± 8.0 m.y. (not significantly different from previous K-Ar dates from a single body). A re-appraisal of the palaeomagnetic data, in the light of the distinct groupings of the directions, yields two significantly different pole positions- Lat 50.7°S, Long. 174.5°E (A₉₅= 5.2°) and Lat. 47.7°S, Long. 123.5° (A₉₅= 9.5°). The former of these is in excellent agreement with pole positions from other Lower to Middle Jurassic rocks of Australia but the significance of the latter remains obscure.