Paleomagnetism of the Pandurra Formation and Blue Range Beds, Gawler Craton, South Australia, and the Australian Mesoproterozoic apparent polar wander path

• Published in: Australian journal of earth sciences 2011-06, Vol.58 (4), p.347-360
• Main Authors: Schmidt, P. W., Williams, G. E.
• Format: Article
• Language: English
• Subjects: Age; Americas; Cratons; Declination; Gallium; Gawler Craton; Inclination; Intervals; Mesoproterozoic; paleomagnetism; polar wander; Poles; red beds; South Australia
• ISSN: 0812-0099; 1440-0952
• DOI: 10.1080/08120099.2011.570377

The Mesoproterozoic Pandurra Formation and Blue Range Beds of the Gawler Craton, South Australia, are undeformed, low-dipping (typically 10-15°) arenites of fluvial origin displaying pale to moderate red colours with light grey mottles and streaks and local Liesegang banding. Eighty-nine core samples and seven block samples were collected from 18 sites in the Pandurra Formation at Whyalla and 70 core samples from 16 sites in the Blue Range Beds at Talia. Specimens from all samples were stepwise thermally demagnetised, revealing hematite as the dominant magnetic carrier with a Neél temperature of 680°C. The mean direction for the Pandurra Formation after tilt-correction (N = 90 specimens) is declination = 248.2°, inclination = 46.7° (α 95  = 4.4°), indicating a paleolatitude of 27.9 +3.9/-3.4° and a pole position at latitude 33.6°S, longitude 64.5°E (A 95  = 4.9°). The mean direction for the Blue Range Beds after tilt-correction (N = 61) is declination = 233.9°, inclination = 50.2° (α 95  = 4.0°), with a paleolatitude of 31.0 +3.7/-3.5° and a pole position at 45.2°S, 59.0°E (A 95  = 4.7°). Combined results for the two units after tilt-correction (N = 151) is declination = 242.6°, inclination = 48.3° (α 95  = 3.1°), indicating a mean paleolatitude of 29.3 ± 2.8° and a mean pole position at 38.4°S, 62.4°E (A 95  = 3.5°). The combined results constitute a positive fold-test with 99% confidence, suggesting that the magnetisation pre-dates tilting. The two pole positions, when compared with Australia's Mesoproterozoic apparent polar wander path, imply ages between 1.5 and 1.2 Ga, in accord with the inferred stratigraphic ages. The pole paths for Australia and North America are sub-parallel from about 1.4 to 1.2 Ga, before diverging. However, during this interval Australia and North America were widely separated, seemingly ruling out their assemblage in some supercontinental reconstruction for that interval.