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The Greca quarry is located in the Colombo municipality, close to the Curitiba Shear Zone, south of the Lancinha Shear Zone in the State of Parana. It is inserted in the Atuba Complex (Curitiba Terrane) and comprises the meridional portion of the Ribeira Belt. This work was carried out by means of field work, petrography, electron backscattered diffraction analysis and strain analysis using the Fry, Polar and Rf/φ methods. Thus, it aims to analyze meso and micro scale strain in tectonites in a key area of the Atuba Complex. The heterogeneous ductile strain observed at a microscopic and macroscopic scale resulted in stromatic, protomylonitic and mylonitic metatexites, of submillimetric to metric widths. The occurrence of quartz and leucocratic veins of centimetric to metric thickness is rare, either discordant or concordant to the foliation of migmatites. Two deformation phases were found, both derived from ductile shear: the first is associated with the thrusting tectonics (Dn-1); and the second has a sinistral transcurrent-transpressive nature (Dn). The presence of new quartz grains observed by subgrain rotation (SGR) recrystallisation and new grains by bulging (BLG) recrystallisation in the feldspar crystals indicates temperatures above 450 °C (lower amphibolite facies) during the shear of both phases. The strain analysis was generated based on the investigation of quartz crystals of 2 samples and 4 thin sections (XZ and YZ planes). The analyzes indicated approximate strain ratios (R) for all methods used in the XZ and YZ planes. Quartz presented values between 2.250 and 1.304 (XZ section) and 2.237 to 1.110 (YZ section). The ellipsoids are mainly oblate and are equivalent to the apparent flattening group. The tectonites are predominantly of S or SL type. According to the EBSD data, it was possible to identify that the strain occurred by dislocation creep mechanisms, associated with the dynamic recrystallisation processes. The samples analyzed by EBSD indicated that the feldspar crystals have poles (010) in the direction and the quartz crystals show the activation of the basal sliding system with the aid of the rhombohedral system. The results also indicate low temperatures, probably due to the retrometamorphic event that occurred in the last strain stage of the Atuba Complex. |
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