Department of Geological Sciences

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Browsing Department of Geological Sciences by Subject "ANOMALIES"

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    Effects of Lightning on the Magnetic Properties of Volcanic Ash
    (Nature Portfolio, 2019) Genareau, Kimberly; Hong, Yang-Ki; Lee, Woncheol; Choi, Minyeong; Rostaghi-Chalaki, Mojtaba; Gharghabi, Pedram; Gafford, James; Kluss, Joni; University of Alabama Tuscaloosa; Mississippi State University; University of North Carolina; University of North Carolina Charlotte
    High-current impulse experiments were performed on volcanic ash samples to determine the magnetic effects that may result from the occurrence of volcanic lightning during explosive eruptions. Pseudo-ash was manufactured through milling and sieving of eruptive deposits with different bulk compositions and mineral contents. By comparing pre- and post-experimental samples, it was found that the saturation (i.e., maximum possible) magnetization increased, and coercivity (i.e., ability to withstand demagnetization) decreased. The increase in saturation magnetization was greater for compositionally evolved samples compared to more primitive samples subjected to equivalent currents. Changes in remanent (i.e., residual) magnetization do not correlate with composition, and show wide variability. Variations in magnetic properties were generally more significant when samples were subjected to higher peak currents as higher currents affect a greater proportion of the subjected sample. The electrons introduced by the current impulse cause reduction and devolatilization of the ash grains, changing their structural, mineralogical, and magnetic properties.
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    Upper mantle seismic anisotropy beneath the Northern Transantarctic Mountains, Antarctica from PKS, SKS, and SKKS splitting analysis
    (American Geophysical Union, 2017-02-12) Graw, Jordan H.; Hansen, Samantha E.; University of Alabama Tuscaloosa
    Using data from the new Transantarctic Mountains Northern Network, this study aims to constrain azimuthal anisotropy beneath a previously unexplored portion of the Transantarctic Mountains (TAMs) to assess both past and present deformational processes occurring in this region. Shear-wave splitting parameters have been measured for PKS, SKS, and SKKS phases using the eigenvalue method within the SplitLab software package. Results show two distinct geographic regions of anisotropy within our study area: one behind the TAMs front, with an average fast axis direction of 42638 and an average delay time of 0.960.04 s, and the other within the TAMs near the Ross Sea coastline, with an average fast axis oriented at 51658 and an average delay time of 1.560.08 s. Behind the TAMs front, our results are best explained by a single anisotropic layer that is estimated to be 81-135 km thick, thereby constraining the anisotropic signature within the East Antarctic lithosphere. We interpret the anisotropy behind the TAMs front as relict fabric associated with tectonic episodes occurring early in Antarctica's geologic history. For the coastal stations, our results are best explained by a single anisotropic layer estimated to be 135-225 km thick. This places the anisotropic source within the viscous asthenosphere, which correlates with low seismic velocities along the edge of the West Antarctic Rift System. We interpret the coastal anisotropic signature as resulting from active mantle flow associated with rift-related decompression melting and Cenozoic extension.