Senior Project Advisor
Kulshan, Mount Baker, Magnetic susceptibility, Magnetite, Ulvöspinel
The aim of this study is to examine variations in the composition of Fe-Ti oxide minerals in the Sulphur Creek lava flow (SE margin of Kulshan), using magnetic techniques and electron microscopy. Geochemical and petrological data from these rocks dated ~9.8 ka may be a product of two distinct magma pulses (Garvey, 2002) with two distinct compositions: andesitic basalt and basalt. The composition of cubic oxides (magnetite and ulvöspinel) is influenced by the geochemistry of the crystallizing magma and can be used to provide information about the chemical evolution of these magmas, but also to help frame future paleomagnetic studies of these flows that can determine the temporal history of their emplacement. In this study, I asses the utility of electron microscopy for identifying precise chemical compositions on the micro-scale and the comparison of the results to those of magnetic experiments. The amount of titanium (Ti) in the magnetite (Fe3O4) - ulvöspinel (Fe2TiO4) solid solution series is directly manifested in its Curie temperature; the temperature at which the grains lose their ability to be permanently magnetized. The Curie temperature of samples from the Sulphur Creek flows were determined using thermomagnetic experiments, which were then used to estimate the composition of these titanomagnetites. These were then compared with the Fe and Ti content of phases observed using the electron microscope equipped with an energy-dispersive spectrometer (EDS). This study produced different results for some of the samples within the andesitic basalt composition between the two methods described above. Reasons for the discrepancy can be inferred by the domain state of the grains, their magnetic behavior, and the lack of precision of the energy-dispersive detector on the SEM for the smallest sizes of Fe-Ti oxides. In addition, I provide data for how the rock magnetic properties are different throughout the flow as an aid in future analyses.
Zilis, Elika, "Using Mineral Magnetism to Characterize Compositions of Fe-Ti Oxide Phases of the Sulphur Creek Lava Flow (Kulshan)" (2023). WWU Honors College Senior Projects. 654.
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