The middle and upper atmosphere radar of Japan is a 46.5MHz, monostatic pulse-Doppler radar with an active phased-array antenna which consists of 475 crossed Yagis. Since 1983, observations of irregularities in the troposphere, stratosphere, mesosphere, and ionospheric F-region have been conducted. Here we will show that the MU radar can be used to get the electron densities of the ionospheric E-region of 90 to 160km height as well. Preliminary results are presented. We compared variations of electron density at different heights for a normal day on September 22, 1987 and for a partial eclipse on September 23, 1987. For the partial eclipse day, the electron densities in the whole E-region began to decrease at around 1030 JST. The duration was about 3 hours, and the decrease of electron density was about 20% relative to a normal day. These results showed that electron densities directly reflect the variation of the solar UV flux.

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A variety of rock-magnetic, paleomagnetic, ore-microscopy and scanning electron microscopy methods have been used to study the magnetic mineralogy and domain structure in samples of a columnar basalt from San Anton (Cuernavaca, Mexico). The basalt presents a rare unique susceptibility variation behaviour with low temperatures. The susceptibility decreases with temperature to about 40-70% of the room-temperature value, and then increases up to about 60-100% at 77K. Results suggest the presence in the columnar basalts of predominantly single and pseudo-single domain titanomagnetites with composition around TM-60, and a small amount of ultra-fine grained superpara-magnetic particles. The titanomagnetites are low-temperature oxidized. Upon heating, these titanomaghemites invert to an intergrowth of titanomagnetite and ilmenite. This increases saturation magnetization and coercivity.

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A paleomagnetic study was carried out on three gabbroic intrusives in the Avalonian terrane of southeastern Cape Breton Island. Thirty five samples (96 specimens) from seven sites were collected for this purpose. Thermal and/or alternating field treatments were performed. Four components of magnetization were detected. One component coincides with the present Earth's field direction. A second component (A) oriented south-southeast with shallow to intermediate inclination (165, +41) is interpreted as representing a Siluro-Devonian overprint. A third component (B) yields a mean direction to the southeast and an intermediate inclination (147, -54). This component is not observed in North American rock units of Devonian age or younger; it is thus bracketed in the Early Devonian-Late Hadrynian interval. Based on magnetic properties, mineralogical and geological grounds, an Ordovician-Cambrian age of acquisition is attributed to this component of magnetization. A fourth component characterized by a low unblocking temperature and median destructive field has a mean direction to the northeast and an intermediate inclination (54, +47). This uncommon direction is inferred to represent an incompletely isolated magnetization. Compaged to low southern paleolatitudes for the Late Hadrynian period of cratonic North America, the paleolatitudes of the Avalonian terrane are slightly higher but this is not really significant. A sea at the most 1000km wide may have separated North America and Avalon at that time. A comparison of the paleolatitude of Avalon and those of Late Hadrynian Atlantic Ocean borderlands indicates that Avalon could have belonged to North Africa at that time. The Avalonian apparent polar wander path in the Devonian-Late Hadrynian interval still remains uncharted. The collision of Avalon with North America occurred most probably at Middle Devonian time.

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Paleomagnetism of Neogene rocks in the Goto Islands and fission-track (FT) geochronology of Miocene igneous rocks in the Goto and Tsushima Islands were investigated in order to reveal Miocene tectonics in the Tsushima Strait area. Untilted directions of primary magnetic components from early to middle Miocene sedimentary rocks in the Goto Islands dominantly showed counter-clockwise (CCW) deflections to the expected direction of the geocentric axial dipole field, while paleomagnetic directions from Miocene igneous rocks and Quaternary basalts were concordant with the expected direction. Zircon FT ages determined on sixteen Miocene igneous rocks show good agreement at about 15Ma. These results, in conjunction with previously-reported paleomagnetic data in the Tsushima Islands, suggest that the Goto Islands were rotated at the early to middle Miocene before about 15Ma and that the CCW of the Tsushima islands occurred after about 15Ma. The CCW rotations of these islands imply that the Tsushima Strait area did not belong to the Southwest Japan block in terms of clock-wise (CW) rotation at about 15Ma, constraining the western margin of the CW-rotated block. The FT ages confine the time of the compressive deformation of pre-middle Miocene sediments in the area to be at the early to middle Miocene before about 15Ma. The CCW rotations of these islands probably took place in response to the movement of the fault system in the area associated with the compressive regime, especially a sinistral motion of the Tsushima-Goto tectonic line. The early to middle Miocene compressive deformation in the area occurred almost coeval with the opening of the Japan Sea. The compressive tectonic regime implies the convergence of the western margin of the Southwest Japan block to the Korean Peninsula during the CW rotation of the block at about 15Ma, which gives a new constraint on the position of the rotation pivot of the block.

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