Oriented Magnetic Field Measurements during IODP Expedition 330 to the Louisville Seamount Chain

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The major objective of this thesis is to reorient and analyze three component magnetic field data recorded in two boreholes during Integrated Ocean Drilling Program (IODP) Expedition 330 to the Louisville Seamount Chain. One aim of the expedition was to determine whether the hotspot that created the seamount chain during the past 80 million years is moving relative to the Hawaiian-Emperor hotspot or if it remained stationary within the mantle. The magnetic field measurements were conducted with the Gottinger Bohrlochmagnetometer, which comprises fibre optic gyros that measure the rotations of the tool within the borehole. In this thesis, I use different algorithms to reorient the measured magnetic field from the tools reference frame into the geographical reference frame. This purpose requires sensors of high accuracy and careful data processing. I present several reorientation algorithms; among others, I introduce two new sensor fusion algorithms for gyro and inclinometer data based on a Kalman filter. Oriented magnetic field data can be used to determine both the inclination and declination of the magnetization of the rocks surrounding the borehole by the application of appropriate models. Measurements on drill core samples can typically only be used to determine the inclination of magnetization, as cores are usually azimuthally unoriented. In the subsequent analysis of the oriented magnetic field data, I use different models for the drilled igneous layers to calculate the magnetization of the subsurface. As horizontal layers turn out to be insufficient to explain the data, I extend the interpretation to inclined layers. I introduce a new approximation for the magnetic field of inclined layers that can be used to separate the calculation of magnetization in an inversion using horizontal layers and a following consideration of potential layer geometries. My approximation additionally reveals possible ambiguities and errors of the measurements. Using images of the borehole wall that give additional information about the possible geometry of a drilled layer inside Burton Guyot (Site U1376), I determine a mean inclination of magnetization of 58.9° and a mean declination of magnetization of 0.4°. These results agree with current theories of a stationary Louisville hotspot. In addition, the result for the declination suggests that Burton Guyot has not been rotated since its formation.