Mylonite zones exposed within the granulite facies terrains of the Ivrea-Verbano zone, northern Italy, and the Bergen Arc, western Norway, provide examples of fault zones in the lower continental crust of extensional and compressional regimes, respectively. Within the Ivrea zone, the shear zones occur as mylonites of the Pogallo fault zone and as high temperature shear zones in the granulite domain of Valle d'Ossola. Deformed ultramafic rocks are also important constituents of deep structural levels of the Ivrea zone. Mylonites in the Bergen Arc are superimposed on an anorthositic complex and are characterized by an eclogite facies mineralogy. The research investigated the seismic properties of rocks from the these zones in order to evaluate the hypothesis that mylonite zones cause deep crustal reflections. The main phases of the work are 1) a sampling program in both regions; 2) investigation of preferred mineral orientations in the mylonitic rocks; 3) thin section and geochemical study of the composition of samples; 4) determination of the elastic constant tensor by measurement of P- and S-wave velocities at confining pressures up to 600 MPa; 4) construction of hypothetical velocity profiles through deformed and undeformed sequences.
