Dating shear zones with plastically deformed titanite: new insights into the orogenic evolution and ore remobilization history of the Sudbury impact structure (Ontario, Canada)

The Sudbury structure is a mineralized impact crater that hosts different families of ore-controlling shear zones with poorly known orogenic affinities. Discriminating whether these deformation events relate to the 1.85 Ga crater modification stage or later regional tectonism, that collapsed the impact structure, is important both for crustal and mineral exploration studies. We have combined underground mapping with isotopic and microstructural analysis of titanite and host minerals in a benchmark ore-controlling mylonitic shear zone of the mining camp, the Six Shaft Shear Zone from the Creighton Mine. Three growth stages of chemically and microstructurally-characterised titanite grains were identified related with the pre-, syn and late deformation stages. In-situ U-Pb age dating of the syndeformational grains demonstrates that metasomatism accompanied crystal-plastic deformation at 1645 ± 54 Ma during the Mazatzalian – Labradorian orogeny (1.7 – 1.6 Ga). This shearing episode led to the plastic deformation and mixed-state remobilization of primary Ni-Cu-PGE sulphide ore bodies to satellite positions during the accretionary growth of Laurentia. The adopted novel petrochronological approach can reveal the age significance of syn-deformational processes and holds promise for the untangling of complex syn-orogenic processes in Precambrian terranes globally.