Investigating Planetary Magnetic Fields : 1. Paleosecular Variation and Relative Paleointensity Curves From Maxwell Bay, Antarctica 2. Rock Magnetic and Remanence Properties of Natural and Synthetic Martian Basalts
Date of Award
Master of Science (MS)
College of Science and Mathematics
Earth and Environmental Studies
Thesis Sponsor/Dissertation Chair/Project Chair
This thesis study investigates two individual projects to determine the paleomagnetic records from sediment core NBP0502-1B from Maxwell Bay Antarctica and SNC Martian meteorite Yamato-908459. Core NBP0502-1B from Maxwell Bay, South Shetland Islands, recovered a 108 m sedimentary record dating between 14.1-14.8 ka. The core has a silty-clay lithology and a calcite based radiocarbon chronology, making this an ideal site to reconstruct an independently dated record of paleosecular variation (PSV) and relative paleointensity (RPI). The interval 0-72 mbsf displays a normal sedimentary fabric, with Kmjn inclination values nearly vertical and Kint and Kmax distributed within the bedding plane. Below 72 mbsf, we observed fabrics with shallow Kmin axes, which may have been caused by deposition on an inclined seafloor. Samples were analyzed for magnetic hysteresis ratios: saturation remanence normalized by saturation magnetization (Mr/Ms) and coercivity of remanence normalized by coercivity (Hcr/Hc). The samples plot in the pseudo-single domain (PSD) region and to the right of the PSD region of the Day Plot. There were no differences in the hysteresis ratios between normal AMS fabrics and those from below 72 mbsf. Curie point analyses have identified four different features in the heating curve; these features have been tentatively identified as titanium-rich titanomagnetite, a magnetic iron sulfide, and two titanomagnetites, with moderate Ti and poor Ti content. Scanning electron microscope analysis supports the Curie point measurements. Samples were also subjected to stepwise alternating field (AF) demagnetization. A low coercivity overprint, likely a drilling or storage overprint was removed at 10-15 mT. The sediments recorded a strong, stable remanent magnetization. Inclinations values between the u-channels and paleomagnetic cubes range from 36.6° to -89.9°, with shallow inclinations often correlating with but not limited to AMS fabrics with non-vertical Kmin values. The maximum angular deviation (MAD) values between the u-channels and paleomagnetic cubes range from 0.2° to 25° and do not correlate with AMS fabric. A preliminary RPI is presented in this thesis.
The study of natural and synthetic Martian meteorite assesses the magnetic recording assemblage and remanence properties of the SNC meteorite Yamato-980459 (hereafter Y- 980459), a primitive member of the shergottite group of Martian meteorites, which was formed under IW +1 fO2. This study is the fourth in series to understand the origin, intensity, and long-term stability of the Mars crustal anomalies detected during the Mars Global Surveyor mission (Acuna et al., 1999). Here we examine samples of natural and synthetic Y-980459 to gain a more representative picture of the magnetic and remanence-carrying abilities of the Mars crust. Our x values are similar to values reported by Hoffman et al., 2010. The NRM and ARM results suggest that there is heterogeneity within the natural Y-980459 and this basaltic shergottite is not a likely carrier of intense crustal anomalies. The synthetic samples lack S, and some chromites adhered to the FePt wires, which affects the x, ARM, IRM and hysteresis parameters. The lack of sulfides in the synthetic samples resulted in lower x, ARM and IRM measurements than their natural counter parts. The combination of this study and previous studies indicate that samples synthesized under fO2 close to IW have the ability to record only, moderate remanences and are not capable of producing the anomalies. Thus, samples synthesized under more oxidizing conditions may be the key to understanding the origin of the Martian magnetic anomalies.
Shah, Deepa, "Investigating Planetary Magnetic Fields : 1. Paleosecular Variation and Relative Paleointensity Curves From Maxwell Bay, Antarctica 2. Rock Magnetic and Remanence Properties of Natural and Synthetic Martian Basalts" (2013). Theses, Dissertations and Culminating Projects. 977.