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An amorphous phase on the anorthite hugoniot
Author(s) -
Campbell Andrew,
Heinz Dion
Publication year - 1993
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/93gl00166
Subject(s) - anorthite , phase (matter) , mineralogy , shock wave , geology , shock (circulatory) , speed of sound , poisson's ratio , thermodynamics , materials science , physics , poisson distribution , mathematics , quantum mechanics , medicine , statistics
Compressional wave velocities as a function of pressure have been measured in pressure‐amorphized anorthite to 14 GPa at room temperature. A weighted linear fit to the data gives a zero‐pressure value of V p = 6.35±0.12 km s −1 , with a slope of 0.154±0.016 km s −1 GPa −1 . It is shown that these compressional wave velocities compare well with bulk sound speeds inferred from shock‐wave experiments on anorthite above the phase transition at 30 GPa, assuming a value of Poisson's ratio in the range of 0.15 to 0.20. All crystalline assemblages which have been suggested as high‐pressure phases of anorthite are shown to possess zero‐pressure bulk sound speeds in the range 6.9 km s −1 to 8.1 km s −1 , well above the value of 5 km s −1 extrapolated from the shock‐wave data. It is therefore proposed that the shock Hugoniot of anorthite above 30 GPa represents the properties of the pressure‐amorphized phase, rather than those of the equilibrium high‐pressure phases.