A determination of the three dimensional seismic properties of anorthosite: comparison between values calculated from the petrofabric and direct laboratory measurements

We have undertaken a coinparative study of the seisnfic properties of an anorthosite. The seisnfic properties have been calculated froIn the lattice preferred orientation (LPO) of plagioclase (90 % by volume) and olivine (10 % by voluine), and the elastic constants of these minerals. Laboratory measurements of Vp (24 directions) and Vs (6 directions) have been made on the same sample at room temperature and pressures up to 1.0 GPa. The twe techniques agree with 0.1 km/s for all orientations tudied when the Voigt averaging method is used. Hill and Reuss averaging methods give calculated velocities significantly lower than the experimental ones. A study of the difference between the velocity values given by the two methods reveals a systematically larger departure in orientations normal to the foliation. The orientation dependent difference between the two tedmiques can be explained if there are small errors in the elastic constants for single crystal plagioclase used in the initial calculations. The axial LPO symmetry of the plagioclase with all the crystallographic b axes parallel to the specimen symmetry axis allowed us to calculate C22 (norInal to (010)) directly from the laboratory measurement of Vp. Some constraints can be put on C22, C44, C66, C12 and C23. On average our data require 10 % modification of the single crystal constants reported by Ryzhova (1964