Schmitt's Thesis Abstract

Virtual Geomagnetic Pole Positions of the Santiam Pass and Boring Lavas

Kate Schmitt

This study examines lava flows which record geomagnetic reversals. Reversals of the earth's magnetic field are poorly understood phenomena, due largely to the few available records of reversals. The number of records of transitions from lavas is especially limited. In this study, a total of 15 basalt flows were studied. Four flows were studied from a sequence of Boring Lavas exposed in an outcrop just off of S.E. Foster Rd. southeast of Portland, Oregon. These lavas are thought to be approximately the same age of the Matuyama-Brunhes Reversal, 775,000 years ago. Eleven flows were studied in two sequences from the central High Cascade Range of Oregon. These sites are located just off of Highway 20 near Santiam Pass, Oregon. These flows are thought to be either Pleistocene or Holocene in age. Scanning Electron Microscope results agree with paleomagnetic results and indicate that titaniferous magnetite is the main carrier of the primary magnetic remanence.

The Boring Lavas yield virtual geomagnetic pole (VGP) positions that cluster off the coast of Antarctica at latitudes between 78.7° S and 64.8° S. A companion study of a sequence of flows overlying these yielded VGP's with similar longitudes, but lower latitudes. VGP positions from these two studies of the Boring Lavas correspond to proposed patches and also lie along one of the proposed preferred longitudinal pathways for VGPs during reversals. The age of the Boring Lavas and the positions of the VGPs suggest that they have recorded part of the Matuyama-Brunhes reversal or one of the shorter polarity events of the early Brunhes or late Matuyama. The Santiam Pass sites yield records of normal and reversed fields, but no transitional fields. Dating is needed to identify which reversals are represented at both locations.

University of Puget Sound