Poisson's ratio of eclogite: the role of retrogression

Available laboratory measurements of combined P- and S-wave velocities of e clogites from the Dabie-Sulu ultrahigh-pressure metamorphic belt and data f rom Manghnani et al. [J. Gcophys. Res. 79 (1974) 5427-5446] show clear posi tive correlations between Poisson's ratio and the intrinsic water content H 2O+ for samples with SiO2 < 56% with the correlation coefficient r of 0.63- 0.72, There are no significant correlations (/r/less than or equal to0.43) between Poisson's ratio and other major oxides. The positive correlations a re interpreted to result from hydration of eclogites during their exhumatio n and exposure at the surface. Our best estimates of the average Poisson's ratios for unaltered quartz-bearing eclogites with H2O+ < 1.0% are 0.24-0.2 5 (+/- 0.01), which is identical to that calculated from single crystal ela stic properties, but lower than the averages (0.27 +/- 0.02) of measurement s compiled by Rudnick and Fountain [Rev. Geophys. 33 (1995) 267-309] and Ch ristensen [J. Geophys. Res. 101 (1996) 3139-3156]. Accordingly, unaltered q uartz-bearing eclogites have Poisson's ratios distinct from mafic granulite s (0.28 +/- 0.01) and marginally different from ultramafic rocks (0.26 +/- 0.02). (C) 2001 Elsevier Science B.V. All rights reserved.