Preliminary studies of natural remanent magnetization of the rocks collected from Ongul Islands, East Antarctica

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A total of 331 rock samples collected from East and West Ongul Islands were studied paleomagnetically. Pyroxene gneiss and the majority of the garnet gneisses have unstable natural remanent magnetization (NRM), whose directions are similar to the present geomagnetic field in the Syowa Station area. These unstable NRMs can be related to the existence of pyrrhotite. Hornblende gneiss, the other garnet gneisses, granite, amphibolite, silicious rocks and pegmatite dykes have stable NRM. Magnetic carriers in stable rocks are considered to be iron oxide minerals (magnetite and hematite). The formations over a wide area of the Lutzow-Holm Bay region were magnetized at the final stage of metamorphism about 480Ma ago in a reversed geomagnetic field direction, then granite intrusions occurred during a period of normal geomagnetic field conditions. The time interval of this sequence may not be very long from the consideration of virtual geomagnetic pole (VGP) positions. Our result of VGP positions (latitude 20.2°S, longitude 20.7°E) supports previous paleomagnetic results obtained from the Lutzow-Holm Bay region and from East Antarctica for early Paleozoic time. VGP positions are located in low latitudes near the presentday Africa.
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