Progressively deformed rocks of the Alpine syn-tectonic Symvolón pluton (northern Greece): results from a multi-scale approach

The syn-tectonic Symvolón pluton is exposed in north-eastern Greece, near the city of Kavala. It represents, together with the akin Vrondou pluton, the south-western termination of the Rhodope Core Complex, which was exhumed as a result of large-scale extension from mid-Eocene to mid-Miocene times. The shear zone developed during this tectonic phase between 300 and 500 °C (Dinter et al., 1995) and affected the early-Miocene (21-22 Ma) granodiorite of the pluton. Effects of progressive deformation are visible at the scale of the outcrop, since field investigation highlighted the presence of a NE-SW monotone stretching lineation consistent with the shape elongation of the outcropping pluton, whose strain increases towards the contact with the host gneiss (Del Moro et al., 1990). In order to define the finite strain boundaries, we carried out a multi-scale investigation that, starting from the field aspects, takes into account quantitative microstructural analysis, minerochemical data and petrophysical features on selected mylonitic rocks. By considering the re-crystallised quartz domains, piezometer calibration of Stipp and Tullis (2003) allowed differential stress to be evaluated (30-220MPa); moreover, the quartz flow-law equation (Rutter and Brodie, 2004) inferred the range of the strain rate (1,02 x 10-13 and 1,01 x 10-12). The petrophysical investigation was carried out at confined pressure conditions (up to 400 MPa), highlighting the seismic properties as related to the structural frame of progressively deformed mylonitic rock. Indeed, fastest compressional waves are oriented within the foliation plane (Vp related anisotropy from 2.16 to 6.92%) and shear wave acoustic birefringence shows its maximum along the stretching lineation direction; finally, Vp/Vs ratios are in the range of 1.67 – 1.70. Finally, mineral chemistry investigation accompanied by multivariate statistical analysis of multi-spectral X ray maps showed that, within original feldspar porphyroclasts compositional zoning is still well preserved, whereas within high-strain domains a complete compositional re-homogenisation was observed