Pallasite meteorites: cosmic ray irradiation and shock-thermal history by the data of track and thermoluminescence analysis

Pallasites are specific stony-iron class of meteorites are mixtures of olivine and Fe-Ni. Olivine is one of the suitable silicate mineral for registration heavy cosmic ray nuclei with help of chemically etched tracks. Five meteorites of this class were selected for study by the track and thermoluminescence (TL) methods: Brenham, Eagle Station, Ilimaes, Marjalahti and Omolon. For measurement of the natural and artificially induced TL it was used high-sensitive TL equipment. The significant difference of the typical glow-curve shapes between pallasites under investigation was determined. The total difference was observed in comparison with TL glow-curves, measured in artificially shocked olivine samples. Note that our TL observations indicate on chief connection with the olivine crystal microstructure and the very low level of possible shock influence recorded in all analysed olivine crystal samples. It was obtained that the shape of the track-density distribution, observed in the Brenham olivine crystals, supports assumption, that this distribution resembles determined irradiated on pre-compaction stage crystals, when the predominant part of tracks represent an addition from the solar cosmic ray VH-nuclei.