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Master of Science (M.S.)
Year Degree Awarded
Month Degree Awarded
Mars, magnetism, terrestrial analog, basalt
Mars was assumed to be very similar to Earth in terms of topography, water, magnetic field, and even the existence of life. However, exploration of the planet in the 1960s by the Mariner missions showed us a very different planet, one very unlike our own. The later discovery by the Mars Global Surveyor (MGS) of the lack of a globally generated magnetic field proved just how different Mars is from Earth. The discovery of strong magnetic remanence (on the order of 20 – 30 A/m) on Mars implies that at some point in Mars’ history there was a magnetic field, and therefore a dynamo. Since a globally active magnetic field is not present, it can also be assumed that the dynamo ceased generation. Basaltic rocks on Earth typically have magnetic remanences between 1 to 4 A/m and do not usually hold on to those remanences for billions of years. In this study, I utilized the information available on the geochemistry, age, and magnetics of Martian rocks in an attempt to find appropriate terrestrial analogs. Seven Earth locations of basaltic rocks (Mauna Loa, Hawaii; Eldgja and Laki eruptions, Iceland; Springerville volcanic complex, Arizona; Taos Plateau volcanic complex, New Mexico; Lascar Volcano, Chile; Tatara-San Pedro volcanic complex, Chile; Patagonia slab window, Argentina) were selected with different tectonic environments, ages, and geochemistries and their rock magnetic properties including natural remanent magnetization (NRM), susceptibility, and hysteresis properties including coercivity were analyzed.
Geochemical values were plotted as averages on a silica vs. alkali graph. There was some variation in NRM and susceptibility values for each of the terrestrial locations (such as Taos Plateau), but overall the averages are a good representation of average NRM and susceptibility. None of the samples studied displayed high remanence, high susceptibility, and high coercivity that would indicate stable single-domain magnetite. Although vastly different basalt origins were studied, an analog to the highly magnetized Martian crust was not found. There are three possibilities for this. 1) A basaltic terrestrial analog does exist, yet it was not included in this study. This is a very viable possibility since there are basalts all over the Earth each with a unique origin. 2) A basaltic terrestrial analog does not exist because although the rocks on Mars are basaltic, the global magnetic field that existed billions of years ago on Mars was unlike that of Earth. Recent work (Stanley et al, 2008) has shown that the Martian magnetic field might be completely different from Earth’s, and therefore a terrestrial analog would be impossible to find. 3) A basaltic terrestrial analog does not exist, but a terrestrial analog of a different rock type does exist. The assumption that the surface rocks on Mars – which are known to be mostly basaltic – are the carrier of the high magnetism. There is the possibility that the surface may be the origin of the magnetism, and in the areas of extremely high magnetism the rocks might locally be different. Also, it may not be the surface rocks that are exhibiting the magnetism. It may be buried highly magnetic rocks under a basalt lava flows.
In addition to seeking out other basalts as terrestrial analogs for to the highly magnetized Martian rocks, it would also be worthwhile to investigate the possibility of a different magnetic field for Mars and what other terrestrial rocks could display such high magnetism billions of years after the termination of the Martian magnetic field.
Laurie L Brown