Kinematics and timing constraints in a transpressive tectonic regime: The example of the posada-asinara shear zone (NE Sardinia, Italy)

Detailed geological field mapping, integrated with meso- and microstructural investigations,kinematic of the flow and finite strain analyses, combined with geochronology, are fundamental toolsto obtain information on the temperature-deformation-timing path of crystalline rocks and shearzone. The Posada-Asinara shear zone (PASZ) in northern Sardinia (Italy) is a steeply dipping km-thicktranspressive shear zone. In the study area, located in the Baronie region (NE Sardinia), the presenceof mylonites within the PASZ, aecting high- and medium-grade metamorphic rocks, provides anopportunity to quantify finite strain and kinematic vorticity. The main structures of the study area arecontrolled by a D2 deformation phase, linked to the PASZ activity, in which the strain is partitionedinto folds and shear zone domains. Applying two independent vorticity methods, we detected animportant variation in the percentage of pure shear and simple shear along the deformation gradient,that increases from south to north. We constrained, for the first time in this sector, the timing of thetranspressive deformation by U-(Th)-Pb analysis on monazite. Results indicate that the shear zonehas been active at ~325-300 Ma in a transpressive setting, in agreement with the ages of the otherdextral transpressive shear zones in the southern Variscan belt.