McKenzie-Johnson's Thesis Abstract

Transitional Geomagnetic Pole Positions Recorded in the Boring Lava Field of Oregon

AlexMcKenzie-Johnson

Reversals of the Earth's magnetic field are a poorly understood phenomena, due largely to the few available records of reversals. The number of records of transitions from lavas is especially limited. This study examines 17 paleomagnetic results from basalt lava flows in a sequence of Boring Lavas exposed on a hillside just off of Foster Road south east of Portland, Oregon. These lavas have been K/Ar dated to be approximately the same age of the Matuyama-Brunhes Reversal, which occurred about 775,000 years ago. Virtual Geomagnetic Pole (VGP) positions from these lavas were found to cluster off of the eastern coast of South America at latitudes between 49° S and 78° S. Hoffman has proposed that VGP positions congregate in one of four patches during a reversal. Others have proposed that the dipole field moves along preferred longitudinal pathways during a reversal. VGP positions from this study correspond to one of the proposed patches and also lie along one of the proposed longitudinal pathways. The age of the Boring Lavas and the positions of the VGPs suggest that they have recorded part of the Matuyama-Brunhes Reversal or a shorter polarity event of the early Brunhes or late Matuyama.

University of Puget Sound