Magnetic properties of howardite, eucrite and diogenite (HED) meteorites: Ancient magnetizing fields and meteorite evolution
The remanent magnetism and other magnetic properties of four howardites (Kapoeta, Petersburg, Le Teilleul and EET 87503), two eucrites (Sioux County and PCA 82502) and three diogenites (Shalka, Johnstown and EET 79002) have been investigated. The dominant carrier of magnetic properties is low-nickel kamacite, present to the extent of 3-5% by weight in Petersburg and 0.1-1% in the others. A wide range of remanent magnetization (NRM) intensities, characteristics and behaviour during alternating field and thermal demagnetization is observed. Two common features are scattered directions of NRM between meteorite subsamples and anomalous behaviour of NRM direction and intensity during demagnetization. All the meteorites show evidence of a primary NRM acquired during an early evolutionary and some acquired secondary NRM. The heterogeneous NRM, with which anomalous demagnetization appears to be associated, implies magnetization of constituent fragments of the meteorite prior to, and no remagnetization after final meteorite assembly. It is tentatively proposed that the primary magnetizing field was of internal origin in the parent body, and that thermoremanent magnetization occurred when the body cooled after differentiation. The coherent magnetic fabric observed in all but two of the HEDs was most probably imparted at the time of final assembly of the meteorites.