Precambrian Palaeomagnetism of Australia

A review of Precambrian palaeomagnetism of Australia: Palaeogeography, supercontinents, glaciations and true polar wander

Authors:

Phillip W. Schmidt

Abstract:

This is the first review of the Australian Precambrian palaeomagnetic database since that undertaken by Idnurm and Giddings (1988) 25 years ago. In this period the data have almost tripled in number from about 60 to more than 170 and while some segments of the pole path are now quite well defined, overall the data are sparse. It is debatable whether the extant rock record amenable to palaeomagnetism is complete enough for full palaeogeographic histories to be reconstructed. The SWEAT connection is apparently ruled out for Rodinia as both the 1200 Ma and 1070 Ma poles from (ancestral) Australia and Laurentia disallow it. However, older palaeopoles do support a SWEAT-like configuration for the pre-Rodinia supercontinent Nuna but the geological reasoning for SWEAT applies to Rodinia so a Nuna SWEAT is less than gratifying. The concept of a "grand-pole" is introduced here, which includes all the "key-pole' features but is predicated on the condition that two or more independent laboratories are in agreement.

Precambrian data from Australia include the oldest palaeopole yet defined, the record of one of the oldest geomagnetic polarity reversals, the most definitive evidence for low-latitude Neoproterozoic glaciation, the first study of BIFs and the timing/nature of iron-ore genesis, the most unusual 'field test' (impact melt rock and ejecta horizon host rocks), some of the best examples of complete contact tests and the timing of craton assembly. Some old caveats that can no longer be ignored, such as corrections for inclination flattening and the permitting of rotations between contiguous intracontinental cratons to bring conflicting palaeopoles into alignment are required. Care should be exercised when inferring palaeolatitudes from sedimentary derived palaeoinclinations. TPW should only be considered if there is evidence from more than one, and preferably more, independent continents. Future work identified includes a complete magnetostratigraphic study of ~ 300 my Adelaidean succession, better age constraints for the Adelaidean and Officer Basin successions and a better age for the Gawler Craton GB dykes.