Palaeomagnetic results for the Jurassic obtained from the Tasmanian dolerites, the Gingenbullen dolerite, the Prospect dolerite, the Gibraltar syenite (all previously examined over a decade ago) and the Garrawilla volcanics, the Nombi extrusives and the Glenrowan intrusives (representing a new study) are presented. It appears that for some rock formations early experimental techniques failed to remove completely secondary components. Evidence suggests that a particularly harsh period of weathering (probably during the Late Cretaceous/Early Tertiary) may be partly responsible for secondary components. Rotational remanent magnetization (RRM) has also been detected and eliminated during alternating field (AF) demagnetization procedures. The results from the Tasmanian doleraites are in close agreement with the previously published results, while those from the other reinvestigations are seen to be markedly different from the early results. In the light of these and other recent data, a new interpretation of the Australian Mesozoic palaeomagnetic pole position is given. The mean Triassic (52° S, 153° E), Jurassic (47° S, 176° E) and Cretaceous (53° S, 152° E) pole positions are now considered as separate. On the basis of the palaeomagnetic data, a spread in age for the Tasmanian dolerite is suggested and the age of the breakup of eastern Gondwanaland is constrained between 100 and 160 My ago. The Australian Jurassic pole position is compared to the Late Triassic–Middle Jurassic palaeomagnetic poles from other southern lands and India in their predrift configuration as dictated by geomorphological reconstructions. It is shown that these poles form a tight group around their mean pole position at 63° S, 71° E (A95= 3°) with respect to present day Africa.
|Number of pages||16|
|Journal||Geophysical Journal of the Royal Astronomical Society|
|Publication status||Published - 1976|