Date of Award

2021

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Geophysics (PhD)

Administrative Home Department

Department of Geological and Mining Engineering and Sciences

Advisor 1

Aleksey V. Smirnov

Committee Member 1

Gregory P. Waite

Committee Member 2

Roohollah Askari

Committee Member 3

Evgeniy V. Kulakov

Abstract

Data on the variation of the direction and strength of Earth’s ancient magnetic field (absolute paleointensity) provide crucial information into the mechanisms of the geodynamo and the Earth’s thermal history. However, the use of conventional methods and instrumentation for absolute paleointensity determination has been hampered by physicochemical alteration of the samples caused by multiple high-temperature cycles and long experiment durations. The reliability and efficiency of the measurement process can be improved by the measurement of the full remanent magnetization vector simultaneously with the temperature cycling of a sample. Such as approach can also substantially expand the scope of materials available for rock magnetic, paleomagnetic, and paleointensity analyses. To date, no commercial instruments and only a few custom-made devices provide this capability. In addition, the existing instruments are not easily accessible, inconvenient, poorly documented, and often characterized by mediocre sensitivity and reliability. In the course of this Ph.D. study, a new full-vector variable-temperature vibrating sample magnetometer (MAG×NEAT) has been developed. The instrument allows fast and fully-automated measurements of magnetic moment as a function of temperature in a range between 20 and 800 °C temperature range. The measurements can be conducted in a vacuum or a controlled atmosphere, which, together with a short duration of thermal treatments, substantially reduces the potential for magneto-mineralogical alteration. The instrument’s capabilities have been utilized to develop a new implementation of the Lowrie method to characterize magnetic mineralogy using a combination of magnetic hysteresis and thermomagnetic analyses. The new approach (the Lowrie-Express method) has been successfully tested on a suite of synthetic and archeological samples. In particular, the method is more effective than conventional rock magnetic techniques in identifying a low Curie temperature and high-coercivity magnetic phase (interpreted as epsilon iron oxide). The new magnetometer has also been utilized to obtain absolute paleointensity with the Thellier-Coe method from six archeological objects from central and northwestern Russia, representing the 13th to 18th century period. The new instrument allows reducing the duration of a paleointensity experiment from several days to several hours, resulting in more reliable, higher quality determinations than the conventional Thellier-Coe method. The new archeointensity and inclination data suggest a period of steeper geomagnetic inclinations and a stronger geomagnetic field in central Russia in the 16th century, followed by a gradual decay in the field strength to its present-day values. These observations are consistent with the existing database for the Eastern European Plain. The results of this dissertation work open new opportunities for using full-vector variable-temperature magnetometry for rock-magnetic and paleointensity investigations.

Creative Commons License

Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License.

Available for download on Thursday, December 15, 2022

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