On the Polar-Wander Path for Australia during the Cenozoic

Abstract

Detailed palaeomagnetic measurements potassium-argon and (K-Ar) dating have been carried out on continuous lava sequences in the Nandewar, Liverpool and Barrington Volcanoes of New South Wales. Consistent K-Ar ages in each case indicate that the volcanoes were built rapidly at 17.5 k0.3 m.yr (Nandewar), 33.7 & 0.7 m.yr (Liverpool) and 5 1.6 k 0.7 m.yr (Barrington), where the errors quoted are the standard deviations. Most of the 150 flows investigated show stable directions of magnetization after magnetic cleaning. Several field reversals are noted and in one instance a series of nine flows records the transition zone from reversed to normal polarity. The frequency and timing of the reversals are consistent with the Cenozoic geomagnetic time scale deduced from the interpretation of marine magnetic anomalies in terms of the sea-floor spreading hypothesis around 17 and 34m.yr, but not at 52 m.yr. It appears that the extrapoIations made in its derivation may no longer be valid at that time. The three new precisely determined palaeomagnetic poles add detail to the Cenozoic polar-wander path for Australia. A steady movement of the South Pole at about 0.45" per m.yr (-5 cm yr-l) is indicated for the past 100 m.yr. This movement is not consistent with a simple northward movement of Australia as inferred from sea-floor spreading data. It indicates in addition a westward excursion of the South Pole, which is attributed to a component of polar wandering superimposed upon the continental drift. * From palaeontological considerations. w m w D. Edwards helped in the collection of samples, and Miss S. Dinter carried out most of the potassium determinations. We gratefully acknowledge their assistance.

Paleomagnetic Results for the Indian and Arabian Plates from Arabian Sea Cores

“…This two-phase history of movement is in accord with that tentatively suggested by Wensink (1973), and the Cretaceous-Eocene rate agrees quite well with his estimate of 30 cm/yr deduced from changes in magnetic inclination within the Deccan traps sequence. It is perhaps surprising to note the relatively rapid northward drift of India in the last 20 m.y., especially when it is seen that Canberra (also on the Indian plate during this period) has moved northward only about 4° in the same period at a mean rate of 2.2 cm/yr (Wellman et al, 1969). Figure 2 also suggests that the Indian plate may even have moved slightly southward between 44 and 24 m.y.…”

“…McElhinny (1968) and Wellman and McElhinny (1970) showed from a study of the Deccan traps that India had moved northward through 50 degrees of latitude in the last 65 m.y., but no paleomagnetic observations were known which indicated the motion of India within this time interval. It was not certain that the rate of northward movement had been constant; Wellman et al (1969) had discovered a sharp bend in the apparent polar wander curve of Australia 25 to 34 m.y. ago, indicating that a change in the direction of motion of the Indo-Australian plate occurred at this time.…”

Motion of the Australian Plate from Sediment Paleoinclinations, Early Cretaceous through Holocene

“…Since the pioneer work by Irving (1956), numerous paleomagnetic studies were conducted in Australia on the Precambrian (e.g., Porath, 1967;Giddings, 1976;Embleton, 1978), the Paleozoic (e.g., Irving, 1966;Luck, 1973;Embleton and Shepherd, 1977), the Mesozoic (e.g., Robertson, 1963;Schmidt, 1976;Embleton and Schmidt, 1977), and the Cenozoic (e.g., Wellman et al, 1969;McElhinny et al, 1974;Idnurm, 1985). The whole Paleozoic to Cenozoic apparent polar wander path (APWP) for Australia was reviewed by Embleton (1981Embleton ( , 1984.…”

Comparative Stratigraphy and Structure of the Western Australian Margin and the Adjacent Deep Ocean Floor

“…3) Australia apparently started wandering northward at the beginning of the Late Cretaceous (Wellman et al, 1969), and by the Santonian it may have reached a critically warmer latitude that favored the deposition of carbonate sediments. This is the weakest of the three speculations, because, with the few exceptions noted above, the onset of carbonate deposition is synchronous over the 26° of latitude of the western margin, whereas according to this speculation, carbonate deposition would be expected to have started in the north and slowly extended southward.…”