Magnetization, paleomagnetic poles, and polar wander on Mars

Using the geometry of an areocentric dipole field, we have remodeled the an omalies observed in the Terra Sirenum and Terra Cimmeria regions by the Mar s Global Surveyor (MGS). For the origin of the anomalies, we used both magn etic stripe and magnetic shell hypotheses. For magnetic stripe models, we a ssume that sea-floor spreading formed the anomalies in the presence of a re versing axial dipole field. We found that a simple magnetic stripe model wi th constant magnetization and crustal thickness results in poor agreement w ith the observed anomalies. However, by allowing the intensity of magnetiza tion to vary freely between and along the stripes, a reasonable fit to the observed data can be found while maintaining the observed polarity along th e stripes. Applying the simple magnetic stripe model to the Terra Sirenun a nd Terra Cimmeria anomalies results in best-fit spreading centers located w ell to the north of the surviving magnetic stripes. This could possibly exp lain the apparent lack of symmetry that has been noted in the anomalies. For the magnetic shell hypothesis, we assume that a monopolarity dipole fie ld magnetized the early crust of Mars. The anomalies that persist today wou ld then be the result of partial demagnetization of the original magnetic s hell by more recent processes. The magnetic anomalies in Terra Sirenum and Terra Cimmeria are consistent with this model, especially if the magnetizat ion of the original magnetic shell was laterally inhomogeneous. If the mono polarity magnetic shell hypothesis is correct, best-fit magnetic paleopole locations for the original magnetization lie in a sub-equatorial belt cente red near the prime meridian. If the ancient magnetic pole of Mars coincided with the spin pole, this result implies that either apparent or true polar wander has occurred on Mars. Apparent polar wander would be consistent wit h plate tectonics having occurred after the formation of the magnetic anoma lies. True polar wander has previously been proposed to explain certain mor phologic features found on Mars. (C) 2000 Academic Press.