Reliability of Ancient Planetary Magnetic Field Intensity Determination Using the Ratio of Thermoremanence to Saturation Isothermal Remanence

Abstract:

Silicate rocks and metal alloys in meteorites preserve the record of ancient planetary magnetic field in the Solar System. In particular, unraveling stable vector information of ancient magnetic field would constraint thermal evolution of meteorites. Despite its importance, extracting reliable ancient planetary magnetic field information is notoriously difficult because meteorites alter irreversibly during heating. We tested the reliability of the ratio of thermoremanent magnetization (TRM) to saturation isothermal remanent magnetization (SIRM). Although the uncertainty of TRM/SIRM was an order of magnitude larger than that of the high-fidelity Thellier-type estimation, the TRM/SIRM was especially useful when dealing with meteorites which are highly susceptible to alteration on exposure to external heat. The ratio of TRM/SIRM is grain-size dependent, as it is larger for finer grains. We also found that metal-poor silicates from highly differentiated planetary bodies tend to show higher ratio of TRM/SIRM.