Publications

We have measured the elastic wave velocities and single-crystal elastic moduli of lawsonite (CaAl2(Si2 O7)(OH)2< middle-dot >H2O) by Brillouin spectroscopy at high temperatures to 450 < degrees >C and at room pressure. Lawsonite is generally characterized by high longitudinal (vP) and shear (vS) 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 vP and vS. 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 vP/vS and Poisson's ratio with increasing temperature at 1 atm pressure. Our results show that the aggregate bulk modulus (KS=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.

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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.