PLIO-PLEISTOCENE EQUATORIAL PALEOINTENSITIES FROM KENYA

A study of Pleistocene lavas from the equatorial Galapagos Islands (latitude ~1ºS) that used a correction for multidomain effects [Wang and Kent, 2013, G-cubed] obtained a mean paleointensity of ~20 µT [Wang et al., 2015, PNAS]. This is about 50% of the present-day value. In a pilot study to check this result, we utilized previously thermally demagnetized Plio-Pleistocene lavas from Mt. Kenya region (latitude ~0º) and Loiyangalani region (latitude ~3ºN) [Opdyke et al., 2010, G-cubed]. We selected 2-3 specimens from each of 30 lava sites from Mt. Kenya region and 31 lava sites from Loiyangalani region with coherent directions and not exhibiting any indications of having been struck by lightning. Our preliminary results show an overall mean paleointensity of ~16 µT. Along with paleointensities from Antarctica (latitude 78ºS) [Lawrence et al., 2009], Iceland (latitude ~64ºN) [Cromwell et al., 2015, JGR] and Galapagos [Wang et al., 2015, PNAS], our preliminary Kenya lava results support a GAD model of the time-averaged field in both direction and paleointensity but which is only ~50% of the present-day field strength. Along with Galapagos data, our Kenya paleointensity results also suggest that there is little longitudinal asymmetry in the GAD for the past few million years.