Pressure-induced amorphization in plagioclase feldspars: A time-resolved powder diffraction study during rapid compression

1Melissa Sims et al.(>10)
Earth and Planetary Science Letters 507, 166-174 Link to Article [https://doi.org/10.1016/j.epsl.2018.11.038]
1Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA
Copyright Elsevier

The pressure-induced amorphization of the two endmembers of the plagioclase ((Na1−xCax)Al1+xSi3−xO8) solid-solution, anorthite (CaAl2Si2O8) and albite (NaAlSi3O8), has been studied as a function of compression rate by means of time-resolved powder diffraction. Anorthite and albite were compressed in a diamond anvil cell to 80 GPa at multiple rates from 0.05 GPa/s to 80 GPa/s. The amorphization pressure decreases with increasing compression rate. This negative strain rate sensitivity indicates a change in deformation mechanism in the plagioclase solid-solution endmembers from brittle to ductile with increasing compression rate. The presented data support the previously proposed shear deformation mechanism for the amorphization of plagioclase. Furthermore, amorphization progresses over a wide pressure range suggesting heterogeneous amorphization, similar to observations based on recovered material from shock-compression experiments of plagioclase. Our experiments support the contention that amorphization pressures for plagioclase may occur at lower pressures than usually considered.

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