Fábricas sin-metamórficas, mecanismos y régimen de la deformación en las granulitas de alta presión de Cabo Ortegal (NO de España)

Abstract

High-pressure granulitic tectonites from shear zones at the contacts between the Bacariza Formation and its bounding units developed after eo-Hercynian subduction, during the initial exhumation of the Cabo Ortegal complex. Structural, petrographic, and crystallographic analysis of these tectonites with the EBSD technique enables us to unravel different, syn-metamorphic, deformation mechanisms in the minerals of the high-pressure granulitic assemblage. Dislocation creep and recovery were the main deformation mechanisms in garnet during peak metamorphism, followed by porphyroclast rigid rotation. The matrix minerals accommodated subsequent ductile deformation, still under high-pressure. Mass transfer, anisotropic growth and dislocation creep dominated deformation of augite. Subgrain rotation-recrystallisation by climbaccommodated dislocation creep operated in plagioclase and dislocation creep by <a>prism-slip in quartz. Subsequent, static amphibolite-facies retrogradation was followed by decompression-related microfracturing during exhumation through medium- to upper crustal realms. Ductile rock deformation was non-coaxial and accommodated a top-to-the-NE displacement of hangingwall blocks