High-pressure investigations on Piplia Kalan eucrite meteorite using in-situ X-ray diffraction and 57Fe Mössbauer spectroscopic technique up to 16 GPa

• Ferrosilite and pyroxene show P21/c to C2/c transition between 3 and 4 GPa.
• Anorthite displays amorphous phase transition at 12 GPa.
• Amorphization in anorthite at 12 GPa implied stress due to shock impact.
• Both XRD and Mössbauer patterns show complementary results.

We report here high-pressure investigations on Piplia Kalan eucrite–a member of HED (Howardite–Eucrite–Diogenite) family from asteroid 4-Vesta based on synchrotron X-ray diffraction (up to 16 GPa) and 57Fe Mössbauer spectroscopy (up to 8 GPa). Dominant with anorthite-rich plagioclase, pigeonite-rich pyroxene and clino-ferrosilite, the sample displayed various phase transitions attaining amorphous character at 16 GPa. These phase transitions of individual components could be explained simultaneously through variations in high-pressure XRD patterns and the Mössbauer parameters. Most prominent P21/c to C2/c transition of pigeonite and ferrosilite was exhibited both as sudden variation in Mössbauer parameters and population inversion of Fe2+ in M1 and M2 sites between 2.9 and 3.8 GPa and variation in intensity profile in XRD patterns at 3.56 GPa. Anorthite seemed to respond more to such impact than other components in the sample. Complete amorphization in anorthite which occurred at lower pressure of ∼12 GPa implied residual stress experienced due to shock impact. The presence of high pressure (monoclinic) phase of pigeonite and ferrosilite at ambient condition in this eucrite sample confirmed earlier suggestions of an early shock event. This report is an attempt to emphasize the role of anorthite in the determination of the residual stress due to impact process in the parent body thus to understand the behavioral differences amongst HED members.

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