Saddleback Basalt as a Terrestrial Analog to Highly Magnetized Martian Crustal Rocks

English Abstract:

The magnetic anomalies detected from rocks located in Mars's southern hemisphere have led to extensive investigations into the mineral assemblage and crystal size of the apparent host rock -- basalt -- and the ancient magnetic field Mars had at 4Ga. The lack of a currently active field on Mars indicates that remanence is the source. Investigations are of two types: investigating the rocks themselves, with an hypothesis that a unique mineral assemblage and/or grain size within the rock allow for it to acquire and retain high magnetization, thus different than most terrestrial basalts; or investigating the original magnetic field on Mars which was able to magnetize basalts with strong and stable remanence. The main purpose of this study is to identify a variety of terrestrial basalts to determine if any have the magnetic properties necessary for high magnetization for long periods of time. Samples were taken from diverse locales including divergent plate boundaries, hot spots, continental volcanic complexes, and volcanic arcs. While the terrestrial samples shared similar geochemical characteristics with Martian samples, the magnetic properties were not comparable and did not have, and most likely not retain, high magnetization over billions of years. However, one flow within the Saddleback Basalt located in southern California has a fairly high magnetization for an Earth basalt and could be analogous to the highly magnetized Martian basalts. This is an interesting development due to the fact that currently the Saddleback Basalt is used to simulate the regolith on Mars for rover missions. NRM values for the Saddleback range from 0.1238 – 43.201 A/m with an average of 3.697 A/m. Hysteresis measurements indicate small PSD-sized grains. Magnetic susceptibility ranges from 0.151 to 5.77 x10^-2 with an average of 1.286x10^-2. The results of this study may indicate the Saddleback Basalt could be a better analog to Martian crustal rocks than previously thought.