Deformation induced decoupling between U-Pb and trace elements in titanite revealed through petrochronology and study of localized deformation

Abstract

In this contribution, we analyzed a pair of mafic samples collected from a recently identified shear zone and its proximal footwall from the Manicouagan Imbricate Zone (MIZ) of the central Grenville Province, Québec, Canada. Titanite petrochronology, metamorphic phase equilibria modelling, trace element thermometry, and electron backscattered diffraction data were used to define a Pressure-Temperature-time-Deformation path for the two samples. An interconnected dislocation network within titanite grains, as outlined with Kerneled Average Misorientation maps, are spatially correlated with variation in the U-Pb system but not with that observed for trace element These results suggest that the U-Pb system was decoupled from trace and rare earth elements and that deformation, rather than interface-coupled dissolution-precipitation reactions or re-crystallisation, was the main driver for this decoupling. In addition to highlighting a potential pitfall of titanite petrochronology, our P-T-t-D path reveals that ductile shear zones were active later than previously suggested within the MIZ.