The characterization of Earth's magnetic field over a broad range of time scales is of fundamental importance for understanding the core dynamo generating mechanism. Recently published results from the Erebus Volcanic Province in Antarctica at 78°S suggested that the high angular dispersion in virtual geomagnetic poles coupled with apparently anomalously low paleointensities may result from dynamic effects associated with the tangent cylinder. An alternative explanation is that the geomagnetic dipole moment of the time-averaged field is in fact only about 50% of the present-day value, which would imply that available paleointensity data from elsewhere are seriously biased. The equatorial belt, which should be least affected by tangent cylinder effects, is poorly represented by reliable paleointensities. We propose to generate paleointensity data from 0-5 Myr-old lava flows from the Galapagos Islands and from Kenya, which have recently provided consistent estimates of low paleosecular variation. The paleomagnetic, rock magnetic and preliminary paleointensity results indicate that these rocks have suitable magnetic properties for Thellier-type paleointensity experiments. Fresh subspecimens are available from most of these sites but we would like to collect additional samples from the Loiyangalani area of Kenya, where the limited data show remarkably coherent and stable magnetizations virtually free of lightning strikes.
Our overall objective is to obtain a robust paleointensity dataset from the same lavas used to estimate paleosecular variation in directions and ideally, to produce a full-vector characterization of the time-averaged field at the Equator. Successful completion of this proposed work will provide a more accurate description of geomagnetic field behavior as a benchmark to gauge latitudinal variations, including possible effects associated with the tangent cylinder, and the underlying character of paleosecular variation in earlier epochs. The project will directly support thesis research of a PhD student and include training in laboratory, field and analytical techniques of general applicability.
