HR: 14:55h
AN: GP22A-06 INVITED     [PDF]
TI: A Mantle Dynamics Perspective on Generating an Early Lunar Dynamo
AU: * Stegman, D R
EM: dstegman@eps.berkeley.edu
AF: School of Mathematical Sciences, Monash University, Bldg 28, Monash University, Clayton, Vic 3800 Australia
AU: * Stegman, D R
EM: dstegman@eps.berkeley.edu
AF: Dept. of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, University of California, Berkeley, Berkeley, CA 94720 United States
AU: Jellinek, M
EM: markj@physics.utoronto.ca
AF: Dept. of Physics, University of Toronto, 60 St. George Street, Toronto, Ont M5S 1A7 Canada
AU: Baumgardner, J
EM: baumgardner@lanl.gov
AF: Theoretical Division, Los Alamos National Laboratory, Mail Stop B216, Los Alamos National Laboratory, Los Alamos, NM 87545 United States
AU: Richards, M
EM: markr@eps.berkeley.edu
AF: Dept. of Earth and Planetary Science, University of California, Berkeley, 307 McCone Hall, University of California, Berkeley, Berkeley, CA 94720 United States
AB: We consider the early thermochemical history of the Moon and specifically address the question of how the Moon could have had an internally generated magnetic field suddenly 'switch-on' somewhat late in its evolution and then just as quickly 'switch-off'. It is commonly assumed the Moon never underwent mantle convection, given the majority of the surface geology is likely the original crust formed nearly simultaneous with the Moon. This can partially be explained by the fact that thermal evolution may well occur under the regime of stagnant-lid convection. Furthermore, there are a few clues that perhaps the Moon possessed a brief, internally generated magnetic field (Cisowski et al., 1983) and by implication, that the interior of the Moon was once convecting. Lunar samples returned from the Apollo missions provide a few which may contain a remnant thermal magnetism, possibly acquired during the Moon's 'magnetic era' (Cisowski et al., 1983). These samples also reveal the near side of the Moon contains large areas flooded with volcanic material, the lunar mare. These mare erupted during a pulse of magmatism beginning 0.5 billion years after the Moon had formed and mostly ended after 1 billion years of activity. We have recently shown (Stegman et al., 2003) that chemical overturn models suggested to explain the eruption of the Maria basalts may also account for the hitherto unexplained existence of a lunar magnetic field (core dynamo) at about the same time (~3-4 billion years ago). In this presentation, we will specifically discuss the plausibility of such a model within the context of current uncertainties of Lunar properties (e.g. core size, core composition, initial conditions, etc.).
DE: 1521 Paleointensity
DE: 5430 Interiors (8147)
DE: 5440 Magnetic fields and magnetism
DE: 5455 Origin and evolution
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting