T264 Petrology and Volcanology of Earth and Other Planets (Posters)

Wednesday, 25 September 2024
8:00 AM - 5:30 PM
Hall D

TEMPERATURE AND REDOX CRYSTALLIZATION CONDITIONS OF THE SOUTHAMPTON PALLASITE

Paper number: T264-1
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The olivine and chromite compositions of the Southampton pallasite have been studied to determine the petrologic (T-fO2) conditions of the planetary body from which the specimen originated. The meteorite contains olivine with a relatively homogeneous forsterite content (Fo88±1), and is therefore classified as pallasite main group (PMG). Chromite is an accessory mineral and occurs either as an inclusion (48) enclosed in olivine or as a massive crystal (4 mm and 1 mm in diameter). In contrast to olivine, the chromite show significant compositional variability in their Cr# (90-96) and Fe# (60-80) values, with the higher values being related to the inclusions and one massive chromite. The estimated equilibrium temperatures, determined by the olivine-spinel geothermometer, are 1400±65°C for the massive chromite and 1000-1400°C for the inclusions, the majority of results cluster around 1200±65°C. A minority of inclusions, hosted by two different olivine, exhibit higher temperatures (1500-1800°C). The fO2 has been estimated using the olivine-spinel oxygen geobarometer, with the aforementioned temperatures (°C) and a pressure of 1 GPa. Experiments at 0.5 and 1.5 GPa have shown that pressure has a negligible effect on fO2. Within the uncertainty range of the EPMA analyses, fO2 estimates indicate reduced conditions for the massive chromite crystals (ΔFMQ=-3) and inclusions (ΔFMQ = -1 to -2), comparable to those of the primitive mantle of Earth and Venus (ΔFMQ = -1 to -2). The minimum estimates for the fO2 at the time the meteorite formed may be preserved by the massive chromite crystals. It is possible that decrease in temperature and increase olivine crystallization caused a slight increase in the oxidation state of the system, as shown by the fO2 of chromite inclusions.

Southampton pallasite planetary science oxygen fugacity chromite spinel

Geological Society of America Abstracts with Programs. Vol. 56, No. 5

doi: 10.1130/abs/2024AM-403811

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