Geomagnetism and magnatic evolution from Iceladic Volcanics

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Field works were performed in Iceland during July 1993 and July 1994. Major effort was directed to the collection of paleomagnetic samples from successive lava flows with ages of Pliocene and Pleistocene. Samples were also collected from historic and prehistoric acidic lava flows for geochemical studies. Experiments using paleomagnetic as well as geochemical samples are under progress in Department of Geophysics and Planetary Physics (DEPP) and Earthquake Research Institute (ERI), University of Tokyo, Department of Earth and Planetary Sciences, Tokyo Institute of Technology, and Institute for Study of Earth's Interior (ISEI). Following is a brief description of various research activities.1.Paleomagnetism of successive lava flows.About 250 lava flows were sampled in each year. Five cores were drilled and orientation was measured in terms of directions of sun, reference, or magnetic directions. For a small number of samples, measurement of natural remanent magnetization was carried out in the field using spinner magnetometer and alternating field demagnetizer.2.K-Ar dating.About 50 samples from Storutjarnir section are now dated by K-Ar method. Potassuim is measurementry flame photometry at ERI,while Argon isotope ratios are measured by mass spectrometer at ISEI.3.Paleointensities.Paleointensity of the earth's magnetic field was studied using Icelandic samples by Thellier's method. Result from Western Iceland indicates that the intensity low at the time of polarity reversal continues sometime after the reversal of direction was completed.4.Secular variation data.With the use of Icelandic data as well as data from other areas worldwide, paleosecular variation (PSV) of the geomagnetic field was studied. A paleointensity database was set up through the compilation of published data, and models of PSV were developed in terms of the randomly varying Gauss coefficients.