Murchison Meteorite - From the Remagnetised Fusion Crust to the Primary Magnetic Record of the Meteorite Interior

During meteorite fall in the Earth atmosphere the edge areas of the meteorite body are heated and remelted due to the air friction. The completely recrystalized layer on the meteorite surface is called fusion crust (Fig. 2) and can be preserved on early finds. Formation of the fusion crust results in heating and cooling of a thin layer on the surface of meteorite.

We studied magnetic properties of Murchison meteorite (CM2) edge parts. Optically distinguishable affected zone is less than 1 mm thick. Magnetic screening of the edge area related to Murchison meteorite indicates that at least 6 mm thick layer is affected by terrestrial TRM acquisition during the entry and landing. The fusion crust NRM (Natural Remanent Magnetization) is about hundred times bigger than NRM of meteorite interior. Interior of Murchison meteorite is magnetically very soft and unstable. In contrast the TRM of fusion crust is stable, and demagnetization behavior, similar to the saturated Murchison sample. The TRM intensity of the affected layer decreases rapidly towards meteorite interior, but keeps its stability (Fig. 1). The measured values are summarized in the table.

Conclusions

The thermal shock during meteorite fall threw the atmosphere play important role in the sample history and its influence onto magnetic record is evident. According to our results the affected zone is at least 6 mm thick. It is important to consider this process during sample selection and magnetic record interpretation. We must select meteoric samples with care and eliminate samples from the meteorite edge.