| Abstract: | Measurements of compressional wave velocity Vp were made in a gas apparatus to 500°C at 10 kbar in three cores of an anisotropic dunite specimen from Twin Sisters Mountain. The axial directions of the three chosen cores coincide with the preferred directions and concentration of olivine crystallographic axes (a 100], b 010], andc 001]).Measured (δVp/δT)p values at 10 kbar in the three cores (−6.7, −5.4 and −6.2 · 10−4 km/sec · deg, respectively), and the mean value for the dunite (−6.1 · 10−4 km/sec · deg) are larger than the Voigt-Reuss-Hill values calculated from single-crystal data. This discrepancy is explained by the presence of internal thermal stresses, due to anisotropic expansion of olivine grains, causing grain boundary cracks to widen.It is concluded that high negative values of (δVp/δT)p for rocks reported in the literature should be carefully evaluated in terms of the formation of new cracks or widening of cracks already present under high pressure-temperature environments. |
