PALEOINTENSITY RESULTS FROM PLEISTOCENE-AGED ALEUTIAN ISLAND VOLCANIC ROCKS

The geocentric axial dipole (GAD) model is thought to explain long-term (10⁵-10⁶ years) behavior of Earth’s magnetic field. The GAD hypothesis assumes that surface field intensity will be twice as strong at the poles than at the equator, and that the dispersion of virtual geomagnetic poles from a given location will increase with latitude. Some recent studies on global paleosecular variation and paleointensity, however, suggest a departure from GAD in some regions, particularly at high latitudes, where there is currently a lack of globally distributed paleointensity and directional data. Relatively few paleomagnetic data are available from the greater Alaska region, therefore the addition of new information will help us better understand the behavior of the geomagnetic field in this area. We present a new paleointensity dataset from Pleistocene-aged volcanic rocks from the Aleutian Island Chain. Samples from Akutan and Tanaga islands (latitude 54° and 51°, respectively) provide new paleointensity data. Of 96 sites sampled, 11 yielded results that passed our selection criteria. The average paleointensity value of these 11 sites is 37.69 µT, noticeably lower than GAD-predicted values of the present-day field (~51° µT). We postulate that a GAD model based on the present day field overly simplifies the magnetic field behavior in this region, and the long-term geomagnetic field in Alaska may be affected by complex regional field structures. Comparisons to existing paleointensity studies of similar age and latitude will develop a broader scope of understanding regarding magnetic field behavior in the Alaska region.