Investigating the Early Martian Magnetic Field Using Chromite in the ALH 84001 Meteorite

The martian meteorite ALH 84001 has been the subject of several previous paleomagnetic studies using traditional moment magnetometers and SQUID microscopy. These studies have shown that the natural remanent magnetization (NRM) in ALH 84001 is heterogeneous at sub-millimeter scales and is carried by inclusions of chromite and carbonate grains. Of these, chromites are primary igneous phases formed at ~4.1 Ga, and may retain information about the early martian dynamo. However, previous works have not characterized the NRM in a population of chromite inclusions due to insufficient spatial resolution. In this work, we use the quantum diamond microscope (QDM) to obtain micrometer-resolution magnetic field maps of ALH 84001 and study the NRM of chromite inclusions. We find that many chromite inclusions are strongly and stably magnetized but in random orientations. This pattern of magnetization appears inconsistent with a classic thermoremanence origin. In order to test whether this unusual remanence may be due to remagnetization by repeated shocks on Mars, we will perform high-pressure demagnetization experiments on ALH 84001 chromites using a non-magnetic diamond anvil cell. The results of these experiments will be combined with measurements of chromite NRM direction and intensity to understand any record of the early martian magnetic field retained in ALH 84001.