Nature of the sources of magnetic anomalies of Mars
Séminaires Planétologie et Sciences Spatiales
Salle 727 - Lamarck A -
Charles University in Prague
Magnetic anomalies are changes in magnetic field detection either along one-dimensional profiles or in two-dimensional surveys. The interpretation of such anomalies is complicated because the anomalies are affected by shape of the magnetic source, the nature of the magnetic interaction with surrounding sources. In this work our effort was primarily on the nature of the magnetic minerals that are causing the magnetic anomalies. Initial motivation was to find out what causes the magnetic anomalies over allochtonous terrains in Labrador Canada. Against common wisdom, that source was due to titanomagnetite, we showed that hematite was the primary carrier in Labrador. This discovery triggered question what is the relation between magnetite and hematite in respect to planetary magnetic anomalies with focus on magnetic anomalies on Mars. We found that magnetic mineral had intrinsic low demagnetizing field that was responsible for near saturation values when cooled within the geomagnetic field (~50 microtesla). The analysis of magnetic mineralogy was extended to titanohematite and we showed that exsolution of the titanohematite lamellae, when slow cooling in crustal conditions, lead to almost magnetically saturated material. With this finding we realized that single domain size of hematite is significantly larger and that exsolution effectively freezes single domain state of hematite giving rise to effective source of crustal magnetic anomalies both on Earth and Mars. This research opened a new way to generalization of magnetic properties of magnetic minerals in general and we used it to formulate an empirical law for acquisition of remanent magnetization for any magnetic mineral. With this tool we were able to clarify magnetic aspect not only for magnetic anomalies detected on Mars from Mars Global Surveyor mission in general, but also for anomalies near large impact craters on Mars. We showed an impact pressure dependence on magnetization due to passing shock wave through the material. We identified zones on Mars that have contrasting magnetic properties and we used magnetic properties of minerals and magnetic map of Mars to interpret tectonic history of Mars.