New late Palaeozoic palaeomagnetic results from Cratonic Australia, and revision of the Gondwanan apparent polar wander path

Abstract

Palaeomagnetic investigation of the Early Carboniferous succession of the Mount Eclipse Sandstone in the Ngalia Basin, the latest Devonian succession of the Brewer Conglomerate in the Amadeus Basin, and the Late Devonian reef complexes in the Canning Basin, has revealed three key poles for calibration of the Gondwanan apparent polar wander path (APWP). The samples were from industrial diamond-drill cores for the first two successions, and from both diamond-drill cores and surface outcrops for the Canning Basin reef complexes. Primary remanences were revealed from all three successions; those from the first two successions passed a fold test, and that from the last succession passed a syndepositional breccia and an allochthonous block test. These results provide three palaeopoles with good palaeohorizontal and magnetization-age constraints for cratonic Australia: a Visean pole (MES) at 37.6°S, 52.6°E with A95 = 8.7°, a latest Devqnian pole (BC) at 47.1°S, 041.0°E with A95 = 6.4°, and a late Frasnian ? early Famennian pole (CB2) at 62.0°S, 023.2°E with A95 = 14.69°. The A95 ellipse of the pole CB2 overlaps with that of the pole CB1 determined by Hurley and Van der Voo (1987) from the same succession. The Late Palaeozoic APWP for Gondwanaland is revised in light of these new results. We find that some of the data from Africa, which are discordant with the Australian data that are discussed here, can be reinterpreted to reconcile their differences with the Australian data. The revised APWP tentatively suggests an Early to Middle Devonian hairpin. It also indicates that Gondwanaland could have rotated counterclockwise around an Euler pole close to Australia during the Late Devonian and earliest Carboniferous. During this postulated rotation, West Gondwanaland drifted across the South pole with an average speed of ~1.5° Myr?1, whereas Australia stayed at low latitude. This tectonic regime changed during mid-Carboniferous when East Gondwanaland drifted rapidly (~1.5° Myr?1) towards the South pole. We argue that it was the latter phase of rapid continental drift that led to the collision in the Namurian between Gondwanaland and Laurussia, and therefore the formation of Pangaea.