Aspects of the validation of magnetic remanence in meteorites

Meteorite magnetic records constitute physical evidence of processes acting during early solar system evolution. Consequently, the validation of these records is important in meteorite research. The first step in the validati on process should be the REM value, The REM value is the ratio of natural r emanence (NRM) to saturation remanent magnetization imparted by a 1 T magne tic field (SIRM). The REM values range over 3 to 4 orders of magnitude for stony meteorites and for chondrules from Allende (C3V-S1), Bjurbole (L4-S1) , and Chainpur (LL3-S1) meteorites. The REM values computed from published NRM and SIRM data identify many orde rs of magnitude range in the REM values including REM values >100 x 10(-3). These data suggest a dependence for the NRM intensity on the curatorial lo cation from which the sample was obtained. Any earth rock acquiring thermor emanent magnetization (TRM) in the geomagnetic field has a restricted range in REM mostly between 5 and 50 x 10(-3), the exception being the mineral h ematite in the multidomain size range, The only terrestrial samples with RE M much greater than 100 x 10(-3) are those struck by lightning. The REM value provides a physical basis for recognition between valid recor ds and those that "might be contaminated," The isothermal remanence acquisi tion (RA) curve is presented as a contamination curve that allows an indica tion of the level of magnetic field contamination required to give the comp uted "REM" (RM/SIRM) value. In the case of the Bjurbole and Chainpur chondr ules, with REM values >100 x 10-3, the RA curve indicates that unrealistica lly large contamination magnetic fields would be required to give REM value s greater than 100 x 10-3. This would suggest contamination other than by a hand magnet that is normally available to an experimenter. This would requ ire an explanation that would involve large magnetic fields during chondrul e formation, or some extraordinary remanence acquisition mechanism that rem ains to be described. Magnetic contamination experiments, using similar to 80 and similar to 40 m T magnets, demonstrate that the "REM" values and extent of modification of the magnetic vector record are mineralogy dependent, and this is mostly rel ated to the amount and characteristics of the mineral tetrataenite. The com plexity of the meteorite records suggest validation of the record as a firs t step. The REM value is the first physical statement that can be made in t his validation.