Direct measurement of 3D elastic anisotropy on rocks from the Ivrea zone (Southern Alps, NW Italy) Z. Pros a , T. Lokajı ´c ˇek a , R. Pr ˇikryl b, * , K. Klı ´ma a a Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic, V holes ˇovic ˇka ´ch 42, 180 00 Prague 8, Czech Republic b Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic Accepted 31 March 2003 Abstract Lower crustal and upper mantle rocks exposed at the earth’s surface present direct possibility to measure their physical properties that must be, in other cases, interpreted using indirect methods. The results of these direct measurements can be then used for the corrections of models based on the indirect data. Elastic properties are among the most important parameters studied in geophysics and employed in many fields of earth sciences. In laboratory, dynamic elastic properties are commonly tested in three mutually perpendicular directions. The spatial distribution of P- and S-wave velocities are then computed using textural data, modal composition, density and elastic constants. During such computation, it is virtually impossible to involve all microfabric parameters like different types of microcracking, micropores, mineral alteration or quality of grain boundaries. In this study, complete 3D ultrasonic transmission of spherical samples in 132 independent directions at several levels of confining pressure up to 400 MPa has been employed for study of selected mafic and ultrabasic rocks sampled in and nearby Balmuccia ultrabasic massif (Ivrea zone, Southern Alps, NW Italy). This method revealed large directional variance of maximum P-wave velocity and different symmetries (orthorhombic vs. transversal isotropic) of elastic waves 3D distribution that has not been recorded on these rocks before. Moreover, one dunite sample exhibits P-wave velocity approaching to that of olivine single crystal being interpreted as influence of CPO. D 2003 Elsevier B.V. All rights reserved. Keywords: Anisotropy; Ivrea zone; Transversal isotropic 1. Introduction Knowledge of the degree of rock fabric anisotropy and its symmetry is of great importance when inter- preting kinematics of the crust and upper mantle (e.g. Christensen and Salisbury, 1979; Silver and Chan, 1991; Ji and Salisbury, 1993; Mainprice and Silver, 1993). The 3D seismic properties and anisotropy of lower crustal and upper mantle rocks are commonly calculated from the crystallographic preferred orienta- tion of major rock-forming minerals (lattice preferred orientation measured by U-stage or neutron diffrac- tion—see, e.g. Nikitin et al., 2001), the single crystal elastic constants, rock density and modal composition (Crosson and Lin, 1971; Peselnick et al., 1974; Main- 0040-1951/03/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0040-1951(03)00176-8 * Corresponding author. Tel.: +420-2-2195-1500; fax: +420-2- 2195-1496. E-mail addresses: tl@irsm.cas.cz (T. Lokajı ´c ˇek), prikryl@mail.natur.cuni.cz (R. Pr ˇikryl). www.elsevier.com/locate/tecto Tectonophysics 370 (2003) 31– 47