We have measured the elastic wave velocities and single-crystal elastic moduli of lawsonite (CaAl
2(Si
2 O
7)(OH)
2< middle-dot >H
2O) by Brillouin spectroscopy at high temperatures to 450 < degrees >C and at room pressure. Lawsonite is generally characterized by high longitudinal (v
P) and shear (v
S) elastic wave velocities. A number of the elastic properties increase with increasing temperature, including the shear modulus, G (< partial-differential >G /< partial-differential >T=+2.01 GPa/100 K), and the aggregate velocities v
P and v
S. These anomalous properties are likely related to a displacive phase transition at < similar-to >0 < degrees >C. This is supported by the small value of the elastic modulus c
66 (18(1) GPa at room temperature), and the fact that c
66 softens as temperature is decreased approaching the < similar-to >0 < degrees >C phase transition. The anomalous behavior in c
66 leads to a decrease in v
P/v
S and Poisson's ratio with increasing temperature at 1 atm pressure. Our results show that the aggregate bulk modulus (K
S=125(2) GPa at 21 < degrees >C) decreases monotonically with increasing temperature ( < partial-differential >K
S / < partial-differential > T =-1.8 GPa/100 K), in contrast to the results of Daneil et al. (1999) who observed a minimum in the bulk modulus at < similar-to >230 < degrees >C. In general, the aggregate elastic wave velocities of lawsonite under high P - T conditions of a subducted slab are expected to remain comparable to those of anhydrous mafic silicates. This observation reinforces the notion that other hydrous minerals persist in subducted oceanic crust to considerable depth (< similar-to >250 km), in order to explain the low velocity layers observed in some subduction zones (e.g. Helffrich, 1996; Abers, 2000). < copyright > 2003 Elsevier Science B.V. All rights reserved.
Schilling, F. R.; Sinogeikin, S. V.; Bass, J. D. (2003):
Single-crystal elastic properties of lawsonite and their variation with temperature.
Physics of the Earth and Planetary Interiors,
136,
1-2,
107-
118.
