ABSTRACT

The study seeks to obtain high-quality paleomagnetic data from normal and reverse polarity lava flows of Pleistocene age (0-1.7 Ma) from Kenya to constrain the time-averaged field at the equator and to determine the Time-Averaged Magnetic Equator. A previous study on equatorial lavas from Ecuador (Opdyke et al., G-cubed, in revision) leads to the hypothesis that the magnetic field at the equator is best modeled with a ~5% axial quadrupole contribution to the geocentric axial dipole field. This model predicts that the geomagnetic field at a latitude of approximately 3 deg. north will be horizontal and represent the position of the Time-Averaged Magnetic Equator whereas at the geographical equator it will be inclined about 4 deg. These differences are small but detectable with the large data sets that we hope to obtain from lavas at the equator in the vicinity of Mt Kenya and about 3 deg. north of the equator in the area around Loyangalani on the east shore of Lake Turkana, where a large volcano, Mt. Kulal, lies just to the east and there are also voluminous lava flows in the Gregory rift on the southern shore of Lake Turkana that can be sampled. Sampling will be done over two years in two sampling trips each of about a month's duration. The time-averaged geomagnetic field is expected to be symmetrical around the Earth's spin axis and this study will test that hypothesis since the region of the proposed study is 135 deg. east from Ecuador. Data will also obtained and processed from samples from 80 sites collected from the Galapagos Islands. Preliminary results for this sample collection were reported by Rochette et al. (1997) and the unused portions of the drill cores will be fully demagnetized. Thellier paleointensity studies will be done on selected samples from both the Kenya and the Galapagos collections in an attempt to obtain a full vector characterization of the paleofield. Therefore, at the conclusion of this study, high-quality paleomagnetic data will be available from three large studies of lavas from near the equator (Equador, Kenya and Galapagos Islands) and these data will greatly increase the knowledge of the configuration of the time-averaged geomagnetic field. Among the broader impacts of this work are training of graduates and undergraduates.

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