A Source for the Martian Crustal Magnetic Field

The magnitude of the martian magnetic crustal field requires intensities of magnetization of large volumes of the martian crust to be stronger than any comparable volumes on Earth [1, 2]. The Martian magnetic field at 4.0 Gyr was about one order smaller than the present geomagnetic field [3-5], and because the generating volume for the martian dynamo is considerably smaller than that for the geodynamo, it seems unlikely that the martian dynamo would ever have been much stronger than the geodynamo. In the absence of evidence for such a strong field on Mars, there is a need for a special model to account for the intensity of magnetization of the source rocks of the Martian anomalies. One potentially relevant feature of early Mars is the presence of water that reacts with atmospheric carbon dioxide to form acidic solutions. These fluids can dissolve igneous rocks in the crust and precipitate iron-rich carbonates, as observed in the older martian meteorites. Here we suggest that thermal decomposition of such iron-rich carbonates due to magmatic intrusions could give rise to plentiful singledomain magnetite and generate a potent source for the martian crustal field.