Constraints on the depth of
magnetized crust on Mars from impact craters
F. Nimmo and M.S. Gilmore, J. Geophys. Res., 106, 12315-12323, 2001.
(PDF file (1731K) available)
Large (diameter greater than ~500 km) Martian impact basins are associated with observed magnetic fields which are
statistically distinct from, and smaller than, fields associated with
smaller craters. We suggest that this effect arises because impacts
cause shock, heating, and excavation, reducing the magnetization of
previously magnetized crust. For a simple, uniformly magnetized model the magnetic field at 100 km altitude is reduced by
~50% when a crater-shaped demagnetization zone reaches the base of
the magnetized layer. By analogy with terrestrial data, we assume that in Martian craters the zone of demagnetization extends to a depth of 0.04-0.15 crater diameters. On the basis of this assumption, the data suggest that
the depth to the base of the magnetized layer on Mars, if uniform, is ~35 km, with
lower and upper bounds of 10 and 100 km, respectively. These bounds imply
magnetizations of 5-40 A/m and are consistent with
likely Mars geotherms at 4 Gyr B.P.
Francis' Page
Department of Earth Sciences
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nimmo@esc.cam.ac.uk
This page was last modified on 2 July 2001.