Australian Precambrian polar wander: a review

Abstract

The Precambrian apparent polar wander path for Australia is revised in the light of new results. As previously, a single path can be drawn through the poles even though these have been derived from different cratonic units. The poles and the path are critically reviewed in an historic context. The pole path is based on the assumptions that the geocentric axial dipole model is a reasonably good approximation for the past geomagnetic field and that the Australian cratonic units have been contiguous throughout geologic time. The validity of the first of these assumptions may be argued from general theoretical considerations and uniformitarian concepts; the second is in essence a working hypothesis which is supported by the location of the poles on a single path. A new kind of analysis of the pole data in terms of accumulated polar wander angles suggests that both assumptions may be regarded as essentially valid. Palaeomagnetic evidence for the global tectonic setting of Australia and the other continents in the Precambrian has led in the past to conflicting interpretations concerning relative movements between the continents. The Precambrian style of global tectonism still remains uncertain but, on balance, the available evidence from palaeomagnetism, geochronology and geology seems at present to favour a quiescence of subduction processes in the Middle and Early Proterozoic, and the dominance of coherent plate motions over collision tectonics by mechanisms such as true polar wander. Australia moved through all zones of latitude during the Precambrian. However, in the few instances where palaeoclimatic indicators are available for comparison, the palaeolatitudes either do not support the uniformitarian assumptions of palaeoclimate or leave the question of uniformitarianism open. The best documented examples of the former are the latest Proterozoic glaciogenic sequences; another example comes from the McArthur Basin; a further possible example is from the western margin of the Yilgarn Block. Although several explanations have been offered for the low latitudes of the latest. Precambrian glacial deposits, none of these appears to be completely satisfactory. Surprisingly, in view of the highly sinuous shape of the pole path, the plot of the accumulated polar wander angle against time consists simply of several straight line segments with abrupt junctions. The linearity of the segments indicates that the rate of polar wander was constant for long periods of time; the abrupt junctions suggest major changes in the style of tectonism.