Thermal demagnetization of Martian upper crust by magma intrusion

[1] The absent or weak magnetic field above large Martian volcanoes may provide constraints on their formation and the carrier of magnetization. We consider the ability of magma intrusions to thermally demagnetize the shallow crust beneath volcanoes through heat conduction and hydrothermal circulation. If magnetization is dominated by magnetite, the volume of crust that is thermally demagnetized is similar to the volume of crust emplaced since the dynamo field disappeared. If magnetization is dominated by pyrrhotite, the volume of crust that is demagnetized is typically more than twice the volume of magma intruded. Hydrothermal circulation contributes negligible additional thermal demagnetization, beyond that from heat conduction alone, for permeabilities less than O(10 ) m. Citation: Ogawa, Y., and M. Manga (2007), Thermal demagnetization of Martian upper crust by magma intrusion, Geophys. Res. Lett., 34, L16302, doi:10.1029/ 2007GL030565.