The rheological properties of rocks in a compressional ductile shear zone, pyllite-quartzite series, Péloponnèse
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XYPOLIAS, P.
The magnitudes of differential stress, strain rate and viscosity during the formation of an extruding crustalscale shear zone (Phyllite-Quartzite Series, PQS) were estimated providing new insights on the mechanical behavior of the middle continental crust of the External Hellenides during compression. The differential flow stress during ductile deformation of PQS, in the Taygetos and Chelmos tectonic windows, has been analyzed using grain-size piezometer. Quartz tectonites from the Taygetos and Chelmos areas have mean grain sizes of 42 μπι and 51 μπι, respectively. Extrapolation of quartzite flow-laws indicates that tectonic extrusion of the PQS occurred at strain rates slightly faster than 10"13s '. These estimates suggest that the extruding zone had a relatively low-viscosity of the order of 1019 to 1020 Pas. Finally, the combination of the obtained strain rate values with published quantitative analyses for the deformation path in the PQS implies that during the initial stage of the tectonic extrusion process the displacement rates parallel to the Taygetos-Parnon and Chelmos Thrusts, were ~6mm/year and 3mm/year, respectively.
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