Strain and deformation history in a syntectonic pluton. The case of the Roses granodiorite (Cap de Creus, Eastern Pyrenees)

The Roses granodiorite is a Variscan stock with well developed syn- and post-magmatic deformation structures that crops out in the Pyrenean Axial Zone. Analysis of structures reveals a continuous deformation history during and after magma cooling. The deformation history is divided on the basis of mechanical behaviour into two stages: an early one with the development of magmatic structures and a late stage with the development of mylonitic fabrics along shear zones. Both stages are separated in time by the emplacement of aplite-pegmatite dykes. Time of dyke emplacement is thought to coincide with a sudden change in rheology of the granodiorite. The abundance of quartz dioritic enclaves permits the use of shape analysis to characterize the magmatic fabric as a homogeneous deformation. Later solid-state deformation led to the development of an inhomogeneous deformation pattern with different sizes of anastomosing shear zones wrapping around lozenge-shaped domains. The displacement/width ratio measured in shear zones ranges between one and two orders of magnitude. The Roses granodiorite is thought to be a synkinematically emplaced stock which records a continuous deformational history with two distinct deformation stages, both recording bulk finite strains of similar order of magnitude but with a marked difference in finite strain distribution. © The Geological Society of London 2004.