Kinematics and vorticity of flow associated with post-collisional oblique transpression in the Variscan Inner Zone of northern Sardinia (Italy)

Abstract

Quartz c-axis fabrics, vorticity of flow and deformation temperatures were analyzed in samples collected in the central sector of the Variscan inner zone in Sardinia (Italy). In order to constrain the kinematics of exhumation of medium- and high-grade metamorphic rocks during D2 post-collisional deformation, we investigated two shear belts with opposing shear senses. These shear belts are developed parallel to the trend of the inner zone which marks the boundary between two metamorphic complexes. Our data suggest that the sinistral shear belt initiated during the early stage of D2 deformation in a simple-shear-dominated regime, whereas the dextral shear belt initiated later in a pure-shear-dominated regime. We document a general non-coaxial flow regime with contemporaneous pure and simple shear components. Geometrical relationships reveal the operation of oblique extrusion during a compressive regime where the coaxial component acted sub-horizontal and orthogonal to the trend of the axial zone. Changes in the kinematics, vorticity of flow and strain geometry that occurred during D2 deformation may be related to post-collisional orogen-parallel displacement caught up in the Variscan orogeny.