Shock-Induced Demagnetization of Pyrrhotite and Implications for the Martian Crust

Details Shock-Induced Demagnetization of Pyrrhotite and Implications for the Martian Crust Shock-Induced Demagnetization of Pyrrhotite and Implications for the Martian Crust

Dec 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufmgp21c..03l&link_type=abstract

American Geophysical Union, Fall Meeting 2004, abstract #GP21C-03

Physics

5440 Magnetic Fields And Magnetism, 6022 Impact Phenomena, 6225 Mars, 1540 Rock And Mineral Magnetism

Scientific paper

Maps of the remanent magnetic field of Mars show demagnetized zones within and around giant impact basins. It is possible that vast regions of the Martian crust were demagnetized due to a phase transition of the magnetic carriers induced by a shock wave. This hypothesis is supported by the fact that around the Hellas and Argyre basins, the magnetized and unmagnetized zones are separated by a peak shock pressure contour line between 1 and 3 GPa. Static pressure experiments at room temperature have indicated that pyrrhotite (Fe7S8) undergoes a phase transition from ferrimagnetic to paramagnetic at ˜2.8 GPa, with rapid loss of magnetization above 1 GPa. Although pyrrhotite is not a major magnetic phase on Earth, it is a common carrier of magnetization in Martian meteorites. No previous experiments have demonstrated that shocks below 3 GPa can induce this phase change and demagnetize pyrrhotite. To investigate this possibility, we performed shock recovery experiments on pyrrhotites (Mrs/Ms ˜0.7) using a gas gun to simulate natural impact events. The experiments were preceded and followed by a suite of material and magnetic characterization measurements (including X-ray diffraction, magnetic hysteresis and low temperature magnetism) to assess the effects of the shock on the crystallographic and magnetic properties of the pyrrhotite. We will present results from experiments achieving shock pressures in the range of 1 to 4 GPa. These experiments serve as an analogue for the demagnetization of crustal rocks on Mars.

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