The Martian crustal field recorded in Antarctic meteorite Grove Mountains 020090

Abstract

AbstractWe present the first rock magnetic and paleomagnetic analyses of the Martian meteorite Grove Mountains (GRV) 020090, a suitable candidate for paleomagnetic study due to its low degree of weathering and shock metamorphism. Petrological and rock magnetic investigation indicates that pyrrhotite is the dominant magnetic mineral in GRV 020090, where it occurs as a primary phase without significant shock metamorphism or alteration. The magnetic grains in GRV 020090 exhibit single‐domain behavior that facilitates high‐fidelity magnetic recording. We obtained a positive fusion‐crust baked contact test, which supports an extraterrestrial origin of the primary remanence in GRV 020090. The nature of the primary remanence was identified as thermoremanence acquired during crystallization of the rock on Mars. Anhysteretic remanent magnetization and isothermal remanent magnetization paleointensity methods indicated paleofield strengths of 1.6 and 2.6 μT, respectively, for the primary remanence. However, the shock pressure that GRV 020090 experienced may have partially demagnetized the primary remanence, leading to underestimated paleointensity values. Therefore, 1.6 μT is regarded as the lower limit on the paleointensity of GRV 020090. This lower limit is higher than the model‐predicted surface magnetic field strength in the source region for GRV 020090, suggesting that it may have recorded a small‐scale crustal magnetic field previously undetected by orbital magnetic data. This small‐scale crustal field is likely generated by the underlying ancient, magnetized layers, as the crustal magnetization of the surficial terrane with lithology similar to GRV 020090 is too weak to produce such a crustal field.