Development of petrofabric within the Kavala syn-tectonic pluton (NE Greece) and insights for the seismic behaviour of extensional shear zones

The Kavala granitoid pluton (NE Greece), whose emplacement and deformation took place in the early Miocene,offers a peculiar opportunity for investigating the textural development related to the extensional shearing events whichaffected the evolution of the southern Rhodope Core Complex. In this view, one important aspect concerns therelationship between progressive deformation, correlated rock fabric and the distribution of seismic properties withinthe shear zone. To this aim, we studied the microstructural, compositional and petrophysical features of a myloniticgranitoid suite that testifies as deformation occurred at various extents. The main assemblage of sheared granodiorites isgiven by quartz, K-feldspar, plagioclase, biotite, white mica with subordinate chlorite and allanite. Feldsparporphyroclasts usually are enveloped by ribbon-like quartz and micaceous matrix. S-C-C' foliations developed duringthe shearing phase are quite common. Calculated and measured seismic properties of mylonite granodiorites pointed outthat, despite the average compressional and shear wave velocity as well as density values are similar (average values:Vp ~5.87 km s−1, Vs ~3.4 km s−1, Vp/Vs = 1.73 and density = 2.65 g cm−3), the Vp- and Vs-related seismic anisotropybecomes progressively marked from the least to the most deformed mylonite specimen (up to Vp anisotropy = 6.92%).This is due to the dramatic microstructural changes (e.g. mica strong alignment, development of quartz ribbons), whichaffect the velocity distribution within the mylonitic granitoids, since the highest P- and S-wave velocities becomeprogressively oriented parallel to the foliation plane, whereas the lowest values are localised normal to foliation. Theobtained results testify the textural control on the seismic properties and this holds important implications in thebehaviour of high strain zones as potential seismic reflectors and on the source of seismic anisotropy. At the same timethey provide an important link between microstructures, tectonics and distribution of seismic properties within a shearzone.