Study
of the crystallization of Fe-rich basalts with application to the origin of
magnetic anomalies on Mars
One
of the most significant results of the Mars Global Surveyor mission was the
detection of intense remanent magnetization features in the ancient southern
highland terrain. Whether the anomalies represent dikes, plutons, or large
igneous provinces, the leading hypotheses proposed to generate the intensely
magnetized crust involve emplacement of magmas that are probably basaltic in
composition. Therefore, interpreting the geology and underlying geodynamics
requires considering the mineralogy and magnetic characteristics of
remanence-carrying materials that crystallize from relevant basaltic liquids,
evaluating the thermal history of their formation, and assessing what
conditions are likely to preserve these mineralsÕ magnetic properties over
billions of years. Stefanie
Brachfeld and I are investigating these processes using a combination of
high-temperature experiments, analytical methods, and magnetic characterization
techniques.
We are studying the effects of variable cooling rate and oxygen fugacity on the magnetic properties of an SNC-derived Martian basalt composition. Oxygen fugacity conditions are varied over a wide range because spacecraft and meteorite studies indicate a variety of possibilities. The MAG/ER space borne experiment observations provide dimensions, intensities, and orientations of crustal magnetic anomalies. These suggest that if the magnetic minerals crystallized from basalt, any single anomaly may result from a large intrusion, a plexus of small intrusions such as dikes or sills, or a buried plateau of extruded lavasÑall possibilities that pertain to distinct thermal histories that we can investigate experimentally. In turn, our experimental and analytical results will include ranges of material properties such as magnetic intensity of remanence that are needed for modeling crustal magnetic anomaly sources.
Hammer, JE, Brachfeld, S, and Rutherford, MJ (2003) An Igneous Origin for Martian Magnetic Anomalies? Lunar and Planet. Sci. Conf. XXXIV,
Houston, TX.
Image Gallery: Marvelous Magnetite