Graduate Thesis Or Dissertation
 

A paleomagnetic study of Recent Cascade lavas

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h128nh99x

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  • Ninety-five oriented samples were obtained from nine Recent Cascade lava flows in Oregon. Directions and intensities of remanent magnetization were measured on a spinner magnetometer which measures directions of magnetization to within 1.2° s.d. Angle measurements were plotted graphically using an equal area projection. Mean directions and statistics were calculated by digital computer. Samples were demagnetized in alternating magnetic fields while being rotated in a two axis tumbling device. All flow means, except one, calculated from the original magnetization vectors are distinct from the present geomagnetic field direction. A correspondence is found between scatter observed in a flow and the type of outcrop sampled (whether natural or man-made). This is believed to be a consequence of excessive blockiness and aa characteristics of the lavas. Results of demagnetization tests indicate low secondary magnetizations. Stability is indicated by lack of anisotropy, lack of isothermal and chemical remanent magnetizations, low viscous magnetization, and divergence of flow means from the present field direction. Flow mean directions for five dated flows are used to trace the secular variation of the paleomagnetic field back to 3000 B.P. This secular variation curve agrees with data taken in southwestern United States for the same period of time. It has generally been found that Recent mean pole positions are coincident with the geographical pole within the limits of error of the data. This study yielded a mean direction distinct from an axial dipole direction. However, the age span is limited as eight of the nine flows have ages between 300 and 3850 years.
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