| Abstract: | Abstract— Evolutionary processes in meteorites and magnetic fields in the early solar system, both spatial and localised in planetary bodies, can leave their imprint in meteorites through the natural remanent magnetization (NRM) and other magnetic properties they impart to them. In the present investigation the Estherville mesosiderite has been studied to enquire whether its magnetic properties can help to resolve any of the uncertainties associated with mesosiderite history and evolution, and to examine evidence for any magnetic fields to which it or its constituent fragments have been subjected. The Estherville sample as received is strongly magnetized, with an initial NRM intensity of 1.4 × 10?3 Am2 kg?1. The NRM of individual fragments broken from the main mass, when referred to common reference axes, is scattered in direction on a scale which ranges from ～ 1 cm down to ～ 1 mm. Alternating field and thermal demagnetization show a range of magnetic stability among the samples and also some secondary NRM, indicating a variety of magnetic histories. Thermomagnetic analyses of matrix and iron-nickel separates show that the dominant magnetic carriers are kamacite and tetrataenite. The non-coherent directions of NRM within the matrix imply the acquisition of an initial NRM by kamacite in the fragments prior to their final accumulation into the mesosiderite material, and the presence of an ambient magnetic field when the fragment material cooled after its formation. If the tetrataenite carrying the primary NRM was formed from the previously magnetized kamacite/taenite during slow cooling after later metamorphic heating, the maximum temperature during the latter event could not have been higher than ～700 °C or the kamacite would have been remagnetized uniformly or demagnetized, according to whether or nor there was an ambient magnetic field present. Susceptibility anisotropy observations indicate the acquisition of anisotropic properties occurred before final accumulation of the meteorite. Shock and flow processes were probably important in producing foliation and lineation respectively in the fragments resulting from brecciation, and there could also be a contribution from larger metal fragments and/or veins. The scattered NRM of the iron-nickel fragments also indicates magnetization prior to emplacement, therefore favouring introduction in the solid rather than the molten form. |
