HR: 08:45h
AN: GP41C-04    [Abstracts]
TI: Paleointensity of the Martian field from SQUID Microscopy
AU: * Weiss, B P
GP41C-04 AF: Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology 54-724, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Fong, L E
GP41C-04 AF: Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 United States
AU: Lima, E A
GP41C-04 AF: Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 United States
AU: Baudenbacher, F J
GP41C-04 AF: Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 United States
AU: Vali, H
GP41C-04 AF: Department of Anatomy and Cell Biology and Facility for Electron Microscopy Research, McGill University, Montreal, QC H3A 2B2 Canada
AB: Crustal magnetic anomalies in the southern Martian hemisphere have intensities an order of magnitude larger than typical crustal anomalies on Earth. Two possible explanations for this difference are that compared to the present-day Earth, Mars has either (i) larger amounts of crustal ferromagnetic minerals or (ii) the crust was magnetized by a larger paleofield. ALH84001, the only pre-Amazonian Martian meteorite, possesses a stable magnetization dating to 4 Ga or earlier. Previous paleomagnetic studies with SQUID moment magnetometers on bulk ALH84001 grains have estimated that the paleointensity of the field which magnetized the meteorite was between 0.1-1 times that of the Earth's present field. However, these estimates may be lower limits on the true paleointensity because the orientation of the magnetization in ALH84001 is spatially heterogeneous on the submillimeter scale. This complication could have profound implications for hypothesis (ii) above. Here we first demonstrate that superconducting quantum interference device (SQUID) microscopy can recover the same magnetization intensity and direction of a well characterized modern-day terrestrial basalt as that measured with a 2G Enterprises SQUID moment magnetometer. A SQUID microscope paleointensity analysis of this basalt gives the expected present day field intensity of a few tens of microtesla. We further show that our new high resolution SQUID microscopy study of ALH84001, which has mapped its heterogeneous magnetization with the highest resolution yet (0.1 mm), favors the upper range of previous paleointensity estimates for the 4 Ga Martian paleofield (e.g., within a factor of several of that of the present-day Earth). However, this field, were it dynamo in origin, is still too weak to easily explain the intensity of the Martian magnetic anomalies.
DE: 1521 Paleointensity
DE: 1540 Rock and mineral magnetism
DE: 1595 Planetary magnetism: all frequencies and wavelengths
DE: 6225 Mars
SC: Geomagnetism and Paleomagnetism [GP]
MN: Fall Meeting 2005