Palaeomagnetic and Rock Magnetic Studies on Cenozoic Basalts from Kyushu, Japan

Some of these Cenozoic basalts are magnetized in either the normal or reversed direction of the axial dipole field but some others are magnetized obliquely. The remanences of the latter are quite as stable as the normal or reversed flows and are interpreted as recording geomagnetic field directions during polarity transitions. When combined with measurements made on rocks from sites some 10 km away from ours, two paths connecting these transitional virtual poles may be traced, one for the lower Pliocene and the other for the upper Pliocene. Both cross central Russia and the Indian Ocean. Palaeosecular variations of the geomagnetic field have been investigated by restricting our studies to flows which yield virtual poles at latitudes higher than 45° and the dispersion of cleaned R.M. directions obtained from such flows agree with world-wide average values. Thermomagnetic, ore microscope and electron microprobe investigations have been made and the shape of the thermomagnetic curves is related to evidence of both low and high temperature oxidation.