Secondary Magnetization of Some Palaeozoic Rocks from Tasmania

A variety of igneous, sedimentary and metamorphic Palaeozoic rocks from Tasmania have similar directions of NRM-steeply upward. Although the mean direction is not significantly difIerent at the 95% confidence level from the present field, its inclination is slightly steeper. Moreover, the palaeomagnetic pole calculated from these directions is closer to Tertiary poles from Australia than to the present pole. On this data it is statistically more probable that the NRMs are of Tertiary rather than recent age. Their characteristics are the same as viscous PTRMs, and they are likely to have been acquired during a period of slightly elevated rock temperatures. This warming-up may have been associated with Tertiary basaltic activity in Tasmania, or with slightly later regional heating over wide areas of eastern Australia, which has previously been suggest-ed on petrological grounds.