Paleomagnetic Results from the Cambro-Ordovician Bowers Supergroup, Northern Victoria Land, Antarctica
- Edmund Stump
Published Online: 16 MAR 2013
Copyright 1986 by the American Geophysical Union.
Geological Investigations in Northern Victoria Land
How to Cite
Schmierer, K. and Burmester, R. (1986) Paleomagnetic Results from the Cambro-Ordovician Bowers Supergroup, Northern Victoria Land, Antarctica, in Geological Investigations in Northern Victoria Land (ed E. Stump), American Geophysical Union, Washington, D. C.. doi: 10.1002/9781118664957.ch4
- Published Online: 16 MAR 2013
- Published Print: 1 JAN 1986
Print ISBN: 9780875901978
Online ISBN: 9781118664957
- Geology—Antarctic regions—Victoria Land
Fieldwork conducted during the 1981–1982 field season in the Lanterman, Solidarity, and Explorers ranges of the Bowers Mountains included paleomagnetic sampling of volcanic and sedimentary rocks of the Cambro-Ordovician Sledgers Group (Solidarity Formation, Molar Formation, and Glasgow Volcanics) and Leap Year Group (Carryer Conglomerate). Paleomagnetic analysis including alternating field (AF) and thermal demagnetization found great variation in intensity and stability of remanent magnetization. Approximately one third of the sites have magnetic directions that are significantly different from one another. The magnetization is of normal polarity, is well defined, and postdates synmetamorphic F1 folding (467–441 Ma), but it may predate much younger deformation. Partial thermal viscous remanent magnetization (PTVRM) is suggested as the remagnetization mechanism by the observation that thermally distributed unblocking is found in all samples. In a laboratory experiment devised to test this idea, AF-demagnitized specimens heated to 300°C for up to 1000 hours acquired PTVRM proportional to log time. Extrapolation shows that PTVRM would exceed the natural remanent magnetization for all samples in less than 1 m.y. Thus the observed magnetization probably was acquired as a PTVRM and was locked in during slow cooling after a thermal event or during uplift. Unacceptably large rotations or translations are required to bring the observed magnetization (D = 337.7°, I = −86.8°, alpha-95 = 3.4°, n = 16) into agreement with expected directions calculated from a Gondwana apparent polar wander path for intervals of known igneous activity between 550 and 160 Ma. The apparent duration of the remagnetization event, exclusive normal polarity, and high precision of the mean direction from the Bowers Supergroup are most consistent with locking in of the remanence by uplift during the Cretaceous normal polarity superchron. Close agreement of the paleomagnetic pole from the Bowers supergroup (77.0°S latitude, 173.5°E longitude, Δp = 6.7°, Δm = 6.8°) with 100 Ma poles from Australia (corrected for drift) substantiates this age of remagnetization. Uplift during this time most likely resulted from the rifting and early separation of Antarctica and Australia (110–90 Ma). The slight disagreement between the Bowers Supergroup pole and the Cretaceous reference pole may be due to deformation during uplift. Alternatively, the discrepancy may in part reflect northward translation along a transform fault on the west side of the Bowers trough during separation of Australia from Antarctica or, possibly, during early to middle Tertiary movement of West relative to East Antarctica.