Magmatic zircons within two sheared gabbroic dykes from the peridotitic
massif of Lanzo (Western-Alps, Italy) revealed evolution of deformation
from crystal plasticity to rigid body rotation during shear zone
evolution. This is the first time that multiple zircon grains have been
analysed in a kinematic context in a shear zone. Zircon grains recorded
crystal plastic deformation activating the commonly inferred < 100
>{001} and < 001 >{100} glide-systems to the newly identified < 001
>{110} glide-system. The exact selection of glide-system could be
dependant of deformation conditions such as pressure, temperature, and
strain rate. Moreover, the activation of one or several glide-systems
within a single grain could be favoured by the primary orientation of
the grains combined with a high strain rate. In these sheared gabbros,
the deformation mechanisms evolve from plastic deformation at low strain
rate conditions to increase strain, strain softening and localisation of
deformation. The progressive shear zone development and the softening of
the matrix relative to the zircon has lead to a switch from
crystal-plasticity to rigid body rotation of zircon. The zircon grains
rigid body rotation involved that their long axes became parallel to the
lineation of the shear zone, causing reorientation and dispersion of the
misorientation axes away from kinematic Y. (C) 2011 Elsevier B.V. All
rights reserved.