Abstract

Two conflicting models have been proposed for the middle Paleozoic position of Gondwana with respect to Euramerica. A pole from Morocco (Msissi Norite) that may be of Late Devonian age suggests that a broad ocean (∼3,000 km) separated the northern continents from Gondwana, whereas results from Mauritania (Gneiguira Supergroup) indicate that this ocean had closed by Devonian time. Detailed thermal and alternating-field demagnetization experiments have been carried out on red and gray limestones from seven sites (89 samples) in an essentially undeformed Late Devonian reef complex, northern Canning basin, Western Australia. After minor tilt correction, the site mean characteristic directions average 42.7°/−28.9° (declination/inclination) with k = 61.6 and α95 = 7.8°. These results position northwestern Australia at 15°S latitude in the Late Devonian, a paleolatitude consistent with the presence of a well-developed reefal sequence. An early age is inferred for these magnetizations on the basis of the occurrence of mixed polarities and the fact that no post-Devonian directions for Australia resemble the observed declinations and inclinations. If the Smith and Hallam reconstruction for Gondwana is used, the paleomagnetic pole calculated for the Late Devonian of Western Australia agrees with the Msissi Norite result from Morocco and suggests that an ocean still separated Gondwana from Euramerica in the Late Devonian. The pole measured from the Gneiguira Supergroup in Mauritania may be based on remagnetizations of late Paleozoic age.

The directions determined from Canning basin limestones are similar in inclination to but differ by 40° in declination from paleomagnetic results from the Upper Devonian Comerong Volcanics, Lachlan fold belt, southeastern Australia. Canning basin samples are from the stable craton, and Comerong Volcanics samples are from the Tasman fold belt. The discrepancy between the two Australian results may be best explained by tectonic rotation of the Comerong Volcanics locality.

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