Constraints on the Source of the Martian Magnetic Anomalies Inferred From Relaxation Time of Remanent Magnetization

The strong magnetic anomalies observed over Mars originate from remanence of deep crust, which should be preserved during 4 billion years. We estimate the relaxation time of remanence carried by various types of magnetite, considering temperature and pressure dependences of magnetic parameters. The estimation shows that acicular-shaped single-domain magnetite is needed to retain the thick magnetized layer during 4 billion years in a low-Urey ratio scenario, whereas acicular-shaped single-domain, equidimensional single-domain, and pseudo-single-domain magnetites can be the source of anomalies in a high-Urey ratio scenario. In each case, fine-grained (<10m) and preferably high-aspect-ratio magnetite in deep crust is needed to explain the observed anomalies.