Normand's Thesis Abstract

Magnetostratigraphy of the Crescent Basalts, Olympic Mountains, Washington

Amanda Normand

Eight volcanic units were sampled in the southern portion of the Olympic Mountains for paleomagnetic analysis and development of a magnetostratigraphy. Demagnetization studies resulted in mean directions with high alpha 95s and small k values. The amount of scatter within the sites may be the result of secondary overprints that have not been removed. This is possibly due to post-eruptive alteration and weak primary signals, so that we were unable to adequately identify the primary signal. All of the outcrops are severely fractured which may cause additional scatter in the data. Alpha 95 values range from 21° to 180°, most averaging between 21° and 70°. Six of the ten k values are in the single digits, and the best on is 61. The usefulness of the resulting magnetostratigraphy is doubtful, at best. The source of the problem was investigated using the Scanning Electron Microscope (SEM) and Reflected Light Analysis (RLA) to determine mineralogical and textural features of the magnetic oxides. The SEM showed three major mineral groups present including oxides, pyroxene, and feldspars. RLA determined that the oxides are ti-magnetites and ilmenites which have been extensively altered to maghemite and hematite. There is also some hematite staining throughout the samples, but no visible hematite crystals present. Fine-grained samples were found to contain more primary magnetic minerals, and could be used for future analysis of this formation if small samples were taken of pillow rims.

University of Puget Sound